TXNM Energy (NYSE: TXNM) readies $400M sale tied to voided Blackstone PIPE

Rhea-AI Filing Summary

TXNM Energy, Inc. (TXNM) is conducting a primary offering of $400,000,000 of common stock under its shelf registration. The shares are listed on the NYSE under the symbol TXNM; the last reported price on August 28, 2026 was $57.64 per share.

TXNM expects to use the net proceeds to repay its $400 million TXNM 2026 Term Loan, a facility maturing January 17, 2029 that currently bears a weighted average interest rate of 5.01%. That loan was incurred to unwind a prior $400 million PIPE Transaction with an affiliate of Blackstone Infrastructure Partners after the New Mexico Public Regulation Commission declared the PIPE void.

As of August 25, 2026, TXNM had 103,046,111 shares of common stock outstanding; this does not include shares reserved under compensation or benefit plans. An affiliate of underwriter Wells Fargo Securities, LLC is a lender under the TXNM 2026 Term Loan and will receive the repayment proceeds, creating a disclosed FINRA Rule 5121 conflict of interest. The offering may dilute existing holders, and TXNM outlines additional risks related to stock price volatility, potential future issuances, and its pending merger with a Blackstone affiliate.

Filing Explained

This preliminary filing does not report a completed stock sale; final share count, pricing, and net proceeds remain unresolved.

The company describes a planned $400 million primary common-stock offering, but labels this supplement preliminary and not an offer; no completed sale or issuance is disclosed, so existing holders could face dilution only if additional shares are issued.

The cover leaves the number of shares, public price, underwriting discounts, and net proceeds blank, so the filing does not yet establish the offering’s share count or cash raised.

A prospectus supplement is intended to state final terms for a specific takedown; this preliminary supplement instead points to a later completion step, including an expected delivery date that is blank.

A final prospectus supplement would resolve the currently blank share count, price, discounts, net proceeds, and delivery date.

Key Figures

Offering size: $400,000,000 of common stock Last reported sale price: $57.64 per share Shares outstanding: 103,046,111 shares +5 more

8 metrics

Offering size $400,000,000 of common stock Primary common stock offering under the prospectus supplement

Last reported sale price $57.64 per share TXNM common stock on the NYSE on August 28, 2026

Shares outstanding 103,046,111 shares Common stock outstanding as of August 25, 2026, excluding reserved and plan shares

TXNM 2026 Term Loan principal $400,000,000 Borrowed July 22, 2026; intended to be repaid with offering proceeds

TXNM 2026 Term Loan interest rate 5.01% Weighted average interest rate as of August 25, 2026

TXNM 2026 Term Loan maturity January 17, 2029 Stated maturity date of the term loan

PIPE Transaction size $400,000,000 8 million newly issued shares at $50.00 per share under Stock Purchase Agreement

Customer count 846,000 customers Residential, commercial and industrial customers served by PNM and TNMP in New Mexico and Texas

Key Terms

PIPE Transaction, TXNM 2026 Term Loan, well-known seasoned issuer, U.S. real property holding corporation, +2 more

6 terms

PIPE Transaction financial

"representing an aggregate investment of $400 million (the “PIPE Transaction”)"

A PIPE transaction is when a publicly traded company sells new shares or convertible securities directly to a select group of private investors, rather than through a public offering. It’s essentially a quick way for a company to raise cash, but it can dilute existing shareholders and often involves a price discount, so investors watch PIPEs for their potential impact on share value and ownership stakes—like a private top-up that changes the size of everyone’s slice of the pie.

TXNM 2026 Term Loan financial

"we entered into a $400 million term loan agreement (the “TXNM 2026 Term Loan”)"

well-known seasoned issuer regulatory

"Because we are a “well-known seasoned issuer,” as defined in Rule 405"

A well-known seasoned issuer (WKSI) is a large, established public company that meets regulatory size and reporting tests and is granted special, faster options to sell new securities to raise money. Think of it like a trusted borrower with a standing credit line: investors and markets see it as more familiar and the company can access capital quickly with less paperwork, which can affect share supply and investor returns.

U.S. real property holding corporation tax

"our common stock constitutes a U.S. real property interest by reason of our status as a U.S. real property holding corporation"

Foreign Account Tax Compliance Act tax

"commonly referred to as the Foreign Account Tax Compliance Act (“FATCA”)) impose a 30% U.S. withholding tax"

lock-up agreements financial

"Our directors and executive officers have entered into lock-up agreements with the underwriter"

A lock-up agreement is a contract that prevents company insiders—founders, employees, and early investors—from selling their shares for a set period after a public stock offering. It matters to investors because it keeps a large block of shares off the market temporarily; when the lock-up ends, those holders can sell and this increased supply can cause the stock price to fall, similar to a timed release that suddenly opens a valve.

Offering Details

secondary/shelf/ATM

Offering

Offering Type secondary/shelf/ATM

Use of Proceeds Net proceeds are expected to be used to repay borrowings under the $400 million TXNM 2026 Term Loan.

FAQ

What is TXNM (TXNM) offering in this 424B5 prospectus supplement?

TXNM Energy, Inc. is offering $400,000,000 of shares of its common stock under a shelf registration. The exact number of shares and per-share public offering price will be set in the final prospectus supplement.

How will TXNM (TXNM) use the proceeds from this common stock offering?

TXNM expects to use the net proceeds from this offering to repay borrowings under its $400 million TXNM 2026 Term Loan. That term loan matures on January 17, 2029 and currently bears a weighted average interest rate of 5.01%.

How many TXNM (TXNM) shares are currently outstanding?

TXNM reports that 103,046,111 shares of its common stock were outstanding as of August 25, 2026. This figure excludes shares reserved under equity compensation, dividend reinvestment, stock purchase, executive savings and 401(k) plans.

What is the relationship between this TXNM (TXNM) offering and the prior PIPE Transaction?

In June 2025, an affiliate of Blackstone Infrastructure Partners invested $400 million in TXNM via a PIPE at $50.00 per share. After New Mexico regulators declared the PIPE void, TXNM borrowed $400 million under the TXNM 2026 Term Loan to repay that amount and now plans to refinance that loan with this equity offering.

Why does the TXNM (TXNM) offering involve a conflict of interest for Wells Fargo?

An affiliate of Wells Fargo Securities, LLC, the underwriter, is a $400 million lender under the TXNM 2026 Term Loan. Because that affiliate will receive at least 5% of the net proceeds upon repayment, FINRA Rule 5121 deems this a conflict of interest.

How might this TXNM (TXNM) offering affect existing shareholders?

TXNM states that issuing additional common stock in this offering may dilute earnings per share and that substantial share issuances, or expectations of them, could adversely affect the trading price of its common stock.

What is the current trading status and recent price of TXNM (TXNM) stock?

TXNM’s common stock is listed on the New York Stock Exchange under the symbol TXNM. The last reported sale price on August 28, 2026 was $57.64 per share, as disclosed in the prospectus supplement.

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Available on EDGAR 08/31/2026 - 04:02 PM Accepted by SEC EDGAR 08/31/2026 - 04:01 PM Learn about SEC filing dates

The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell these securities and we are not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-285426

SUBJECT TO COMPLETION, DATED AUGUST 31, 2026

PRELIMINARY PROSPECTUS SUPPLEMENT
(To Prospectus Dated February 28, 2025)

TXNM Energy, Inc.

$400,000,000 of Shares of Common Stock

We are offering $400,000,000 of shares of our common stock, no par value (“common stock”), pursuant to this prospectus supplement and the accompanying prospectus.

Our common stock is listed on the New York Stock Exchange (the “NYSE”) under the symbol “TXNM.” The last reported sale price of our common stock on the NYSE on August 28, 2026 was $57.64 per share.

Investing in our common stock involves risks. See “Risk Factors” beginning on page S-4 of this prospectus supplement to read important factors you should consider before investing in our common stock.

Neither the Securities and Exchange Commission (the “SEC”) nor any other regulatory body has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

			Per Share			Total
Public offering price			$			$
Underwriting discounts and commissions(1)			$			$
Proceeds before offering expenses, to us			$			$

(1) See the section titled “Underwriting (Conflicts of Interest)” for additional information regarding total underwriter compensation.

The underwriter expects to deliver the shares of common stock on or about , 2026.

______________

Wells Fargo Securities

Prospectus Supplement dated , 2026.

TABLE OF CONTENTS

Prospectus Supplement

Page

Prospectus Supplement Summary			S-1
Risk Factors			S-4
Where You Can Find More Information			S-6
Disclosure Regarding Forward-Looking Statements			S-7
Use of Proceeds			S-10
Material U.S. Federal Income and Estate Tax Considerations for Non-U.S. Holders			S-11
Underwriting (Conflicts of Interest)			S-15
Legal Matters			S-21
Experts			S-21

Base Prospectus

Page

About This Prospectus			1
Where You Can Find More Information			3
TXNM Energy, Inc.			4
Risk Factors			4
Disclosure Regarding Forward-Looking Statements			5
Use of Proceeds			5
Description of Debt Securities			6
Description of Common Stock and Preferred Stock			16
Description of Warrants			19
Description of Securities Purchase Contracts			22
Description of Units			23
Plan of Distribution			24
Legal Matters			26
Experts			26

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of the offering and certain other matters relating to us and our financial condition. The second part, the accompanying base shelf prospectus, gives more general information about securities we may offer from time to time, some of which does not apply to this offering. The accompanying base shelf prospectus dated February 28, 2025 is referred to as the “accompanying prospectus” in this prospectus supplement. Generally, when we refer to the prospectus, we are referring to both parts of this document combined. If this prospectus supplement is inconsistent with the accompanying prospectus, you should rely on the information in this prospectus supplement.

You should rely only on the information contained in this document or to which this document refers you, or in other offering materials filed by us with the SEC. This prospectus supplement, the accompanying prospectus and any free writing prospectus that we prepare or authorize contain and incorporate by reference information that you should consider when making your investment decision. We have not, and the underwriter has not, authorized anyone to provide you with different information and, if given, you should not rely on it. We take no responsibility for, and can provide no assurance as to the reliability of, any different or inconsistent information. This document may only be used where it is legal to sell these securities. We are not, and the underwriter is not, making an offer of these securities in any jurisdiction where the offer is not permitted. You should not assume that the information in this prospectus supplement, the accompanying prospectus or the documents incorporated by reference herein or therein is accurate as of any date other than the date on the front of those documents. Our business, financial condition, results of operations and prospects may have changed since the date of such information.

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PROSPECTUS SUPPLEMENT SUMMARY

The following information supplements, and should be read together with, the information contained or incorporated by reference in other parts of this prospectus supplement and the accompanying prospectus. This summary highlights selected information from this prospectus supplement and the accompanying prospectus. As a result, it does not contain all of the information you should consider before investing in our common stock. You should carefully read this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference, which are described under the caption “Where You Can Find More Information” in this prospectus supplement and the accompanying prospectus.

Unless otherwise indicated or unless the context otherwise requires, all references in this prospectus supplement to “TXNM,” “TXNM Energy,” “the Company,” “we,” “our” and “us” refer to TXNM Energy, Inc. and its subsidiaries. Unless otherwise indicated, financial information included or incorporated by reference herein is for TXNM Energy, Inc. and its subsidiaries on a consolidated basis.

TXNM Energy

TXNM is a holding company with two regulated electric utilities, Public Service Company of New Mexico (“PNM”) and Texas-New Mexico Power Company (“TNMP”), serving approximately 846,000 residential, commercial, and industrial customers in New Mexico and Texas. TXNM was incorporated in the State of New Mexico in 2000 and its common stock trades on the NYSE under the symbol “TXNM”.

TXNM’s vision is to create a clean and bright energy future while fulfilling its purpose to work together with customers and communities to meet their energy needs. TXNM’s core values of Safety, Caring and Integrity are the foundation for the Company’s business objectives focused on safety excellence and customer satisfaction, including reliability. To reach these objectives, the Company is committed to:

•Preparing our workforce with the knowledge and skills to thrive in a customer-focused world

•Purposefully delivering an intentional customer experience that exceeds our evolving customer and stakeholder expectations

•Enabling an environmentally sustainable future and deploying technologically advanced solutions that empower and benefit customers

•Demonstrating the relationship between customer excellence and our dedicated focus on financial strength

Meeting the business objectives above will drive key financial results:

•Earning authorized returns on regulated businesses

•Delivering long-term earnings growth, with a dividend payout ratio between 50 and 60 percent of earnings

•Maintaining investment grade credit ratings

The Company believes that maintaining strong and modern electric infrastructure is critical to ensuring reliability and supporting economic growth. PNM and TNMP strive to balance service affordability with infrastructure investment to maintain a high level of electric reliability and to deliver a safe and superior customer experience. Both PNM and TNMP seek cost recovery for their investments through general rate cases, periodic cost of service filings, and various rate riders.

Our executive office is located at 414 Silver Ave. SW, Albuquerque, New Mexico 87102-3289, and our telephone number is (505) 241-2700.

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The Offering

Issuer			TXNM Energy, Inc.
Common Stock Offered by this Prospectus Supplement			shares of TXNM common stock.
Common Stock to be outstanding following this offering			shares of TXNM common stock.(1)
Use of Proceeds			We expect to receive net proceeds from this offering of approximately $ million after deducting the underwriting discounts and commissions and estimated offering expenses payable by us. We intend to use the net proceeds that we receive from this offering to repay borrowings under our TXNM 2026 Term Loan (as defined herein). See “Use of Proceeds.”
Listing			Our common stock is listed on the NYSE under the symbol “TXNM.”
Dividend Policy			We expect to pay dividends on our common stock in amounts determined from time to time by our board of directors. Future dividend levels will be dependent on our results of operations, financial position, cash flows and other factors.
Material U.S. Federal Income and Estate Tax Considerations for Non-U.S. Holders			Material U.S. federal income and estate tax considerations of the acquisition, ownership and disposition of our common stock for non-U.S. holders are described in “Material U.S. Federal Income and Estate Tax Considerations for Non-U.S. Holders” included elsewhere in this prospectus supplement.
Transfer Agent and Registrar			The transfer agent and registrar for our common stock is Computershare Trust Company, N.A.
Risk Factors			An investment in our common stock involves various risks, and prospective investors should carefully consider the matters discussed under the caption entitled “Risk Factors” on page S-4 of this prospectus supplement.
Conflicts of Interest			We will use the net proceeds from this offering to repay the TXNM 2026 Term Loan which includes amounts we owe to an affiliate of Wells Fargo Securities, LLC (“Wells Fargo”) who has extended to us loans under such debt as described under “Use of Proceeds” in this prospectus supplement. Because an affiliate of Wells Fargo will receive the net proceeds from the sale of shares of our common stock in connection with the repayment of the TXNM 2026 Term Loan, Wells Fargo is deemed to have a conflict of interest under Financial Industry Regulatory Authority, Inc. (“FINRA”) Rule 5121 as its affiliate will receive at least 5% of the net proceeds from this offering. Accordingly, Wells Fargo, who will be conducting the distribution of our common stock in this offering in accordance with FINRA Rule 5121, will not be permitted to confirm a sale to an account
1 Based on 103,046,111 shares of our common stock outstanding as of August 25, 2026. Excludes (i) any additional shares reserved for issuance under our equity compensation awards or other stock compensation plans or dividend reinvestment and stock purchase plan and (ii) shares issuable under our executive savings plans and 401(k) plan.

S-2

over which it exercises discretionary authority without first receiving specific written approval from the account holder. The appointment of a “qualified independent underwriter” (as defined in FINRA Rule 5121) is not necessary for this offering because the shares of common stock being offered have a “bona fide public market” (as defined in FINRA Rule 5121). See “Underwriting (Conflicts of Interest) – Conflicts of Interest” in this prospectus supplement.

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RISK FACTORS

An investment in our common stock involves certain risks. Our business is influenced by many factors that are difficult to predict, involve uncertainties that may materially affect actual results and are often beyond our control. In addition to the risk factors set forth below, you should carefully consider the risks and uncertainties, as well as any cautionary language or other information, contained or incorporated by reference in this prospectus supplement and the accompanying prospectus, including the information under the caption “Item 1A Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2025, as modified by our other SEC filings filed after such annual report, which will be incorporated by reference in this prospectus supplement, before investing in our common stock. Those risks and the risks set forth below are those that we consider to be the most significant to your decision whether to invest in our common stock. If any of the events described therein occur, our business, financial condition or results of operations could be materially harmed. As a result, the trading price of our common stock could decline, and you could lose all or part of your investment. In consultation with your own financial and legal advisers, you should carefully consider, among other matters, the discussions of risks that we have incorporated by reference before deciding whether an investment in this offering is suitable for you. See “Where You Can Find More Information” on page S-6.

The trading price of our common stock has been and could continue to be volatile.

The trading price of our common stock has been and could continue to be volatile. It is impossible to predict whether the price of our common stock will rise or fall. The price of our common stock could be subject to wide fluctuations in the future in response to many events or factors, including those discussed in the risk factors herein and in our Annual Report on Form 10-K for the year ended December 31, 2025, as well as those delineated under “Disclosure Regarding Forward-Looking Statements” in this prospectus supplement, many of which events and factors are beyond our control.

You may experience significant dilution as a result of this offering, which may adversely affect the per share trading price of our common stock.

This issuance of common stock in this offering may have a dilutive effect on our earnings per share. The actual amount of dilution from the issuance of common stock in this offering or from any future offering of our common or preferred stock, will be based on numerous factors, particularly the use of proceeds and the return generated on those proceeds, and cannot be determined at this time.

The issuance of substantial numbers of shares of common stock or securities convertible into shares of common stock, or the perception that those issuances might occur, could materially adversely affect us, including the per share trading price of shares of our common stock, and could be dilutive to our stockholders.

The vesting of equity awards granted to certain directors, executive officers and other employees under our equity incentive plans and other issuances of our common stock could have an adverse effect on the per share trading price of our common stock, and may adversely affect the terms upon which we may be able to obtain additional capital through the sale of equity securities.

Any future issuance of preferred stock may cause the price of our common stock to decline, which may negatively impact your investment.

Our board of directors is authorized to issue series of shares of preferred stock without any action on the part of the holders of our common stock. Our board of directors also has the power, without the approval of the holders of our common stock, to set the terms of any such series of shares of preferred stock that may be issued, including the designations, preferences, limitations and relative rights, voting, redemption and other rights over our common stock with respect to dividends or if we liquidate, dissolve or wind up our affairs and other terms. Any preferred stock we may issue in the future will rank senior to all of our common stock with respect to the payment of dividends or upon our liquidation, dissolution or winding up of our affairs. If we issue preferred stock in the future that has preference over common stock with respect to the payment of dividends or upon our liquidation, dissolution or winding up of our affairs, or if we issue preferred stock with voting rights that dilute the voting power of our

S-4

common stock, the market price of our common stock could decrease, which may negatively impact your investment.

Future offerings of debt securities, which would rank senior to our common stock upon our bankruptcy or liquidation, may cause the price of our common stock to decline, which may negatively impact your investment.

In the future, we may attempt to increase our capital resources by making offerings of debt securities, including debt securities that are convertible into our common stock (“convertible securities”). Upon bankruptcy or liquidation, holders of our debt securities and lenders with respect to other borrowings will receive a distribution of our available assets prior to the holders of our common stock. Our decision to issue debt securities in any future offering will depend on market conditions and other factors that may be beyond our control. As a result, we cannot predict or estimate the amount, timing or nature of our future offerings, and purchasers of our common stock in this offering bear the risk of our future offerings of debt securities.

In addition, if we issue any convertible securities, we will be required to reserve a number of shares of our common stock for issuance upon conversion of such convertible securities. The conversion of some or all of such convertible securities could dilute the ownership interests of existing shareholders, unless we satisfy any such conversions solely with cash, and conversions of the convertible securities into shares of our common stock, or the perception that such conversions may occur, could adversely affect the trading price of our common stock.

S-5

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports and other information with the SEC, and these filings are publicly available through the SEC’s website at www.sec.gov.

This prospectus supplement and the accompanying prospectus, which include information incorporated by reference, are part of a registration statement on Form S-3ASR we have filed with the SEC relating to the common stock offered hereby. As permitted by the SEC’s rules, this prospectus supplement and the accompanying prospectus do not contain all of the information included in the registration statement and the accompanying exhibits and schedules we file with the SEC. You should read the registration statement and the exhibits and schedules for more complete information about us and our common stock.

The registration statement, exhibits and schedules are also available through the SEC’s website.

You may obtain a free copy of our filings with the SEC by writing or telephoning us at our principal executive offices: TXNM Energy, Inc., 414 Silver Ave. SW, Albuquerque, New Mexico, 87102-3289, Attention: Shareholder Services, telephone number (505) 241-2868. The filings are also available through the Investors section of our website: www.txnmenergy.com. The information on our website is not incorporated into this prospectus supplement by reference, and you should not consider it a part of this prospectus supplement.

We are “incorporating by reference” in this prospectus supplement and the accompanying prospectus information we file with the SEC, which means that we are disclosing important information to you by referring you to those documents. Our combined filings with the SEC present separate filings by TXNM, PNM and TNMP. Information contained therein relating to an individual registrant is filed by that registrant on its own behalf and each registrant makes no representation as to information relating to other registrants. The information we incorporate by reference is considered to be part of this prospectus supplement, unless it is updated or superseded by the information contained in this prospectus supplement or the information we file subsequently with the SEC on or after the date hereof and prior to the termination of the offering that is incorporated by reference in this prospectus supplement.

We are incorporating by reference the following documents that we have filed with the SEC and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act on or after the date hereof and prior to the termination of the offering (except those portions of filings that relate to PNM or TNMP as separate registrants), other than, in each case, any information in such filings that is deemed not to be “filed” with the SEC:

•Our Annual Report on Form 10-K for the fiscal year ended December 31, 2025;

•Our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2026 and June 30, 2026;

•Our Current Reports on Form 8-K as filed on January 2, 2026, March 3, 2026, March 3, 2026, March 31, 2026, June 2, 2026 (only with respect to Item 8.01), June 11, 2026, July 6, 2026, July 20, 2026 (only with respect to Items 1.01 and 2.03), July 21, 2026 and August 19, 2026;

•All information in our Definitive Proxy Statement on Schedule 14A filed on April 28, 2026, to the extent incorporated by reference in our Annual Report on Form 10-K for the fiscal year ended December 31, 2025; and

•The description of our common stock contained in our Exhibit 4.1 to our Annual Report on Form 10-K for the fiscal year ended December 31, 2025, filed with the SEC on February 27, 2026, including any amendments or reports filed for the purpose of updating such description.

S-6

DISCLOSURE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus, and the documents they incorporate by reference contain statements that are not historical fact and constitute “forward-looking statements.” When we use words like “anticipate,” “believe,” “could,” “estimate,” “expect,” “intend,” “may,” “objective,” “outlook,” “plan,” “project,” “possible,” “potential,” “should,” “will,” “would” and similar expressions, or when we discuss our strategy or plans, we are making forward-looking statements. Forward-looking statements are not guarantees of performance. They involve risks, uncertainties and assumptions. Our future results may differ materially from those expressed in these forward-looking statements. These statements are necessarily based upon various assumptions involving judgments with respect to the future and other risks, including, among others:

•the failure of Troy ParentCo LLC (“Parent”) to obtain any equity, debt or other financing necessary to complete the pending merger between Troy Merger Sub Inc. (“Merger Sub”), a direct subsidiary of Parent and TXNM, as contemplated by the Agreement and Plan of Merger dated May 18, 2025 between TXNM, Parent and Merger Sub (“Merger Agreement”), pursuant to which Merger Sub will merge with and into TXNM with TXNM surviving the merger as a direct wholly owned subsidiary of Parent and affiliate of Blackstone Infrastructure Partners L.P. (the “Merger”);

•the expected timing and likelihood of completion of the Merger, including the timing, receipt and terms and conditions of any required governmental and regulatory approvals of the pending Merger that could reduce anticipated benefits or cause the parties to abandon the transaction;

•the occurrence of any event, change or other circumstances that could give rise to the termination of the Merger Agreement, including in circumstances requiring TXNM to pay a termination fee;

•the receipt of an unsolicited offer from another party to acquire TXNM’s assets or capital stock that could interfere with the Merger;

•the outcome of any legal proceedings, regulatory proceedings or enforcement matters that may be instituted relating to the Merger;

•risks related to disruption of management time from ongoing business operations due to the Merger;

•the risk that the Merger and its announcement could have an adverse effect on the ability of TXNM to retain and hire key personnel and maintain relationships with its customers and suppliers, and on its operating results and businesses generally;

•the announcement and pendency of the Merger, during which TXNM is subject to certain operating restrictions, could have an adverse effect on TXNM’s businesses, results of operations, financial condition or cash flows;

•the costs incurred to consummate the Merger;

•the risk that the price of TXNM’s common stock may fluctuate during the pendency of the Merger and may decline significantly if the Merger is not completed;

•The ability of PNM and TNMP to recover costs and earn allowed returns in regulated jurisdictions and the impact on service levels for PNM customers if the ultimate outcomes do not provide for the recovery of costs and operating and capital expenditures, as well as other impacts of federal or state regulatory and judicial actions;

•The ability of the Company to successfully forecast and manage its operating and capital expenditures, including aligning expenditures with the revenue levels resulting from the ultimate outcomes of regulatory proceedings;

•Uncertainty surrounding the status of PNM’s participation in jointly-owned generation projects;

•Uncertainty regarding the requirements and related costs of decommissioning power plants and reclamation of coal mines, as well as the ability to recover those costs from customers, including the potential impacts of current and future regulatory proceedings;

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•The impacts on the electricity usage of customers and consumers due to performance of state, regional, and national economies, energy efficiency measures, weather, seasonality, alternative sources of power, advances in technology and other changes in supply and demand;

•Uncertainty related to the potential for regulatory orders, legislation or rulemakings that provide for municipalization of utility assets or public ownership of utility assets, including generation resources, or which would delay or otherwise impact the procurement of necessary resources in a timely manner;

•The Company’s ability to maintain its debt, including convertible debt, and access the financial markets in order to repay or refinance debt as it comes due and for ongoing operations and construction expenditures due to disruptions in the capital or credit markets, actions by ratings agencies, and fluctuations in interest rates resulting from any negative impacts from regulatory proceedings, actions by the Federal Reserve, entry into the Merger Agreement, geopolitical activity, including tariffs, or the risk of wildfires and storms;

•The risks associated with the cost and completion of generation, transmission, distribution, and other projects, including uncertainty related to regulatory approvals and cost recovery, the ability of counterparties to meet their obligations under certain arrangements (including renewable energy resources, approved power purchase agreements and energy storage agreements), and supply chain or other outside support services that may be disrupted;

•The potential unavailability of cash from TXNM’s subsidiaries due to regulatory, statutory, or contractual restrictions or subsidiary earnings or cash flows;

•The performance of generating units, transmission systems, and distribution systems, which could be negatively affected by operational issues, fuel quality and supply chain issues (disruptions), unplanned outages, extreme weather conditions, wildfires, storms, terrorism, cybersecurity breaches, and other catastrophic events, including the costs the Company may incur to repair its facilities and/or the liabilities the Company may incur to third parties in connection with such issues beyond the extent of insurance coverage;

•State and federal regulation or legislation relating to environmental matters and renewable energy requirements, the resultant costs of compliance, and other impacts on the operations and economic viability of PNM’s generating plants;

•State and federal regulatory, legislative, executive, and judicial decisions and actions on ratemaking, tariffs, and taxes, including guidance related to the interpretation of changes in tax laws, the Inflation Reduction Act of 2022, the Infrastructure Investment and Jobs Act of 2021, the One Big Beautiful Bill Act and other matters, including a government shutdown and the cancellation of grants or related funding;

•Risks related to climate change, including potential financial and reputational risks resulting from increased stakeholder scrutiny related to climate change, litigation and legislative and regulatory efforts to limit greenhouse gas emissions, including the impacts of the New Mexico Energy Transition Act;

•Employee workforce factors, including cost control efforts and issues arising out of collective bargaining agreements and labor negotiations with union employees;

•Variability of prices and volatility and liquidity in the wholesale power and natural gas markets, including the impacts to transmission margins;

•Changes in price and availability of fuel and water supplies, including the ability of the mine supplying coal to Four Corners Power Plant and the companies involved in supplying nuclear fuel to provide adequate quantities of fuel;

•Regulatory, financial, and operational risks inherent in the operation of nuclear facilities, including spent fuel disposal uncertainties;

•The impacts of decreases in the values of marketable securities maintained in trusts to provide for decommissioning, reclamation, pension benefits, and other postretirement benefits, including potential increased volatility resulting from actions by the Federal Reserve to address inflationary concerns and international developments;

•Uncertainty surrounding counterparty performance and credit risk, including the ability of counterparties to supply fuel and perform reclamation activities and impacts to financial support provided to facilitate reclamation and decommissioning at the San Juan Generating Station;

•The effectiveness of risk management regarding commodity transactions and counterparty risk;

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•The outcome of legal proceedings, including the extent of insurance coverage; and

•Changes in applicable accounting principles or policies.

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USE OF PROCEEDS

We expect to receive net proceeds from this offering of approximately $ million after deducting the underwriting discounts and commissions and estimated offering expenses payable by us. We intend to use the net proceeds that we receive from this offering to repay borrowings under our TXNM 2026 Term Loan.

On May 18, 2025, TXNM, Parent and Merger Sub entered into the Merger Agreement, pursuant to which Merger Sub will merge with and into TXNM, with TXNM surviving the Merger as a direct wholly owned subsidiary of Parent. Concurrently with the execution of the Merger Agreement, TXNM and Troy TopCo LP (“Purchaser”) entered into a Stock Purchase Agreement dated May 18, 2025 (the “Stock Purchase Agreement”), pursuant to which Purchaser agreed to purchase 8 million newly issued shares of TXNM’s common stock at a price of $50.00 per share, representing an aggregate investment of $400 million (the “PIPE Transaction”). The PIPE Transaction closed in June 2025 and was intended to provide interim financing to support TXNM’s operations during the period preceding consummation of the Merger. Parent, Merger Sub and Purchaser are affiliates of Blackstone Infrastructure Partners L.P. On July 2, 2026, the New Mexico Public Regulation Commission (“NMPRC”) issued a final order (the “Final Order”) declaring that the (i) PIPE Transaction is void and of no effect and (ii) TXNM, Public Service Company of New Mexico (“PNM”), Parent, and certain of their affiliates (the “Merger Parties”) must file a compliance report demonstrating how they have effectuated the unwinding of the PIPE Transaction.

On July 17, 2026, we entered into a $400 million term loan agreement (the “TXNM 2026 Term Loan”) with the lenders party thereto and Wells Fargo Bank, National Association (“WFB”), as Administrative Agent and affiliate of Wells Fargo. The TXNM 2026 Term Loan is effective as of July 17, 2026 and has a maturity date of January 17, 2029. On July 22, 2026, we borrowed the full $400 million loan amount under the TXNM 2026 Term Loan and paid such amount to Purchaser in full repayment of the $400 million previously paid by Purchaser under the Stock Purchase Agreement in connection with unwinding the PIPE Transaction as a result of the Final Order. As of August 25, 2026, we had $400 million outstanding under the TXNM 2026 Term Loan, with a weighted average interest rate at of 5.01%.

WFB, an affiliate of Wells Fargo, has extended to us the $400 million under the TXNM 2026 Term Loan and accordingly will receive the proceeds from this offering pursuant to the repayment of the TXNM 2026 Term Loan. See “Underwriting (Conflicts of Interest)—Conflicts of Interest” in this prospectus supplement.

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MATERIAL U.S. FEDERAL INCOME AND ESTATE TAX CONSIDERATIONS

FOR NON-U.S. HOLDERS

The following discussion summarizes material U.S. federal income and (to the limited extent set forth below) estate tax considerations relevant to the acquisition, ownership and disposition of shares of our common stock, but does not purport to be a complete analysis of all potential U.S. federal income and estate tax considerations. This discussion only applies to shares of our common stock that are purchased in this offering by Non-U.S. Holders (as defined below), and that are held as capital assets within the meaning of Section 1221 of the Internal Revenue Code of 1986, as amended (the “Code”). This summary is based on the Code, administrative pronouncements, judicial decisions and regulations of the Treasury Department, changes to any of which subsequent to the date of this prospectus supplement may affect the tax consequences described herein. This discussion does not describe all of the U.S. federal income tax considerations that may be relevant to Non-U.S. Holders in light of their particular circumstances or to Non-U.S. Holders subject to special rules, such as certain financial institutions, tax-exempt organizations, insurance companies, traders or dealers in securities or commodities, persons holding shares of our common stock as part of a straddle, hedge, conversion transaction or other integrated or risk-reduction transaction, shareholders that acquired our common stock through the exercise of employee stock options or otherwise as compensation or through a tax-qualified retirement plan, persons that directly, indirectly or constructively hold in excess of 5% of our common stock, “controlled foreign corporations,” “passive foreign investment companies,” real estate investment trusts, regulated investment companies, governmental organizations, qualified foreign pension funds (or any entities all of the interests of which are held by a qualified foreign pension fund), persons subject to the alternative minimum tax, persons required to accelerate the recognition of any item of gross income with respect to our common stock as a result of such income being recognized on an applicable financial statement or certain former citizens or residents of the United States. This discussion does not address any U.S. federal income or estate tax consequences for any beneficial owner of shares of our common stock that is a United States person within the meaning of Section 7701(a)(30) of the Code (a “United States person”) or any entity or arrangement treated as a partnership for U.S. federal income tax purposes. Furthermore, this discussion does not describe the effect of U.S. federal estate (except to the limited extent set forth below), generation-skipping or gift tax laws, the Medicare tax on investment income or the effect of any applicable foreign, state or local laws. Persons considering the purchase of shares of our common stock are urged to consult their tax advisors with regard to the application of the U.S. federal income and estate tax laws to their particular situations as well as any tax consequences arising under other U.S. federal laws or the laws of any state, local or foreign taxing jurisdiction.

We have not and will not seek any rulings or opinions from the Internal Revenue Service (the “IRS”) with respect to the matters discussed below. There can be no assurance that the IRS will not take a different position concerning the tax consequences of the acquisition, ownership or disposition of shares of our common stock or that any such position would not be sustained.

Prospective investors should consult their own tax advisors with regard to the application of the U.S. federal income and estate tax considerations discussed below to their particular situations as well as the application of any state, local, foreign or other tax laws, including gift tax laws.

For purposes of this summary, a “Non-U.S. Holder” means a beneficial owner of shares of our common stock that is an individual, corporation (or entity treated as a corporation for U.S. federal income tax purposes), estate or trust and, for U.S. federal income tax purposes, is not: (i) an individual that is a citizen or resident of the United States; (ii) a corporation or other entity treated as a corporation for U.S. federal income tax purposes that is created or organized under the laws of the United States, any state thereof or the District of Columbia; (iii) an estate the income of which is subject to U.S. federal income taxation regardless of its source; or (iv) a trust if (A) a court within the United States is able to exercise primary supervision over its administration and one or more United States persons have the authority to control all substantial decisions of such trust, or (B) the trust has made an election under the applicable Treasury regulations to be treated as a United States person. If a partnership, or other entity or arrangement treated as a partnership for U.S. federal income tax purposes, holds shares of our common stock, the tax treatment of a partner in such a partnership will generally depend upon the status of the partner and the activities of the partnership. Partners in a partnership holding shares of our common stock should consult their tax advisors as to the particular U.S. federal income tax considerations relevant to the acquisition, ownership and disposition of such shares of our common stock applicable to them.

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Distributions

In general, a distribution that we make to a Non-U.S. Holder with respect to shares of our common stock will constitute a dividend for U.S. federal income tax purposes to the extent paid out of our current or accumulated earnings and profits as determined under the Code. To the extent the amount of a distribution exceeds our current and accumulated earnings and profits, such excess will constitute a return of capital and will first reduce the Non-U.S. Holder’s adjusted tax basis in our common stock, but not below zero, and then will be treated as gain from the sale of our common stock (see “—Sale or Other Taxable Disposition of Our Common Stock” below). Dividends paid to a Non-U.S. Holder that are not effectively connected with the Non-U.S. Holder’s conduct of a trade or business within the United States will generally be subject to U.S. federal withholding tax at a rate of 30% of the gross amount of the dividends (unless such dividend is eligible for a reduced rate under an applicable income tax treaty). In order to obtain a reduced rate of withholding under an applicable income tax treaty, a Non-U.S. Holder is generally required to provide to the applicable withholding agent an IRS Form W-8BEN or IRS Form W-8BEN-E (or a suitable substitute form) properly certifying such Non-U.S. Holder’s eligibility for the reduced rate. Non-U.S. Holders that do not timely provide the applicable withholding agent with the required certification, but that qualify for a reduced withholding rate, may obtain a refund of any excess amounts withheld by timely filing an appropriate claim for a refund with the IRS. Non-U.S. Holders should consult their tax advisors regarding their entitlement to benefits under an applicable income tax treaty and the timing and manner of claiming the benefits.

Dividends that are effectively connected with a Non-U.S. Holder’s conduct of a trade or business within the United States (and, if an applicable income tax treaty so requires, are attributable to a permanent establishment maintained by the Non-U.S. Holder in the United States) are not subject to U.S. federal withholding tax but generally will be subject to U.S. federal income taxation on a net-income basis in the same manner as if such dividends were received by a United States person. The Non-U.S. Holder is generally required to provide to the applicable withholding agent a properly executed IRS Form W-8ECI (or a suitable substitute form) in order to claim the exemption from U.S. federal withholding tax. In addition, a “branch profits tax” may be imposed at a 30% rate (or a reduced rate under an applicable income tax treaty) on a foreign corporation’s effectively connected earnings and profits for the taxable year, as adjusted for certain items.

Sale or Other Taxable Disposition of Our Common Stock

Subject to the discussions below under “—Information Reporting and Backup Withholding” and “—Foreign Account Tax Compliance Act,” a Non-U.S. Holder generally will not be subject to U.S. federal income or withholding tax with respect to gain, if any, recognized on the sale or other taxable disposition of shares of our common stock unless (i) the gain is effectively connected with the conduct by such Non-U.S. Holder of a trade or business within the United States (and, if an applicable income tax treaty so requires, is attributable to a permanent establishment maintained by the Non-U.S. Holder in the United States), (ii) in the case of a Non-U.S. Holder that is a nonresident alien individual, such Non-U.S. Holder is present in the United States for 183 or more days in the taxable year of the disposition and certain other conditions are satisfied, or (iii) our common stock constitutes a U.S. real property interest by reason of our status as a U.S. real property holding corporation (a “USRPHC”) for U.S. federal income tax purposes.

In the case described in (i) above, gain recognized on the disposition of shares of our common stock generally will be subject to U.S. federal income taxation on a net-income basis in the same manner as if such gain were recognized by a United States person, and, in the case of a Non-U.S. Holder that is a foreign corporation, may also be subject to the branch profits tax at a rate of 30% (or a lower applicable treaty branch profits tax rate). In the case described in (ii) above, the Non-U.S. Holder will be subject to a 30% tax (or a lower applicable treaty rate) on any capital gain recognized on the disposition of shares of our common stock (after being offset by certain U.S.-source capital losses).

Generally, a U.S. corporation is a USRPHC if the fair market value of its U.S. real property interests equals or exceeds 50% of the sum of the fair market value of its worldwide real property interests and its other assets used or held for use in a trade or business (all as determined for U.S. federal income tax purposes). We have not determined whether we are a USRPHC; however, even if we are or become a USRPHC, so long as shares of our common stock continue to be regularly traded on an established securities market, within the meaning of applicable Treasury regulations, a Non-U.S. Holder will not be subject to U.S. federal income tax on the disposition of shares

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of our common stock if the Non-U.S. Holder has not held more than 5% (directly, indirectly or constructively) of our total outstanding common stock at any time during the shorter of the five-year period preceding the date of disposition, or such Non-U.S. Holder’s holding period. If our common stock were not considered to be regularly traded on an established securities market, a Non-U.S. Holder (regardless of the percentage of shares of our common stock owned) generally would be subject to U.S. federal income tax on a taxable disposition of shares of our common stock at the regular rates applicable to United States persons and a 15% withholding tax generally would apply to the gross proceeds from such disposition.

Non-U.S. Holders should consult their tax advisors regarding the U.S. federal income tax consequences of investing in our common stock if we were to be treated as a USRPHC. Non-U.S. Holders should also consult their tax advisors regarding potentially applicable income tax treaties that may provide for different rules.

Information Reporting and Backup Withholding

Payors must report annually to the IRS and to each Non-U.S. Holder the amount of any distributions paid to such holder (whether or not the distribution represents a taxable dividend) the name and address of the recipient and any tax withheld with respect to such distributions, regardless of whether withholding was required. Copies of the information returns reporting such distributions and withholding also may be made available to the tax authorities in the country in which the Non-U.S. Holder resides under the provisions of an applicable tax treaty.

A Non-U.S. Holder may be subject to backup withholding for dividends paid to such holder unless such holder certifies on IRS Form W-8BEN or IRS Form W-8BEN-E (or another appropriate form) that it is a Non-U.S. Holder (and the payor does not have actual knowledge or reason to know that such holder is a United States person), or such holder otherwise establishes an exemption.

Information reporting and, depending on the circumstances, backup withholding may apply to the proceeds of a sale or other taxable disposition of our common stock by a Non-U.S. Holder within the United States or conducted through certain U.S.-related financial intermediaries, unless the beneficial owner certifies on IRS Form W-8BEN or IRS Form W-8BEN-E (or another appropriate form) that it is a Non-U.S. Holder (and the withholding agent does not have actual knowledge or reason to know that the beneficial owner is a United States person), or such owner otherwise establishes an exemption.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules may be allowed as a refund or a credit against a Non-U.S. Holder’s U.S. federal income tax liability provided the required information is timely furnished to the IRS.

Foreign Account Tax Compliance Act

Sections 1471 to 1474 of the Code and related IRS guidance (commonly referred to as the Foreign Account Tax Compliance Act (“FATCA”)) impose a 30% U.S. withholding tax on any dividends on our common stock and (subject to proposed Treasury regulations discussed below) on the gross proceeds from a disposition of our common stock, in each case if paid to a “foreign financial institution” or a “non-financial foreign entity” (including, in some cases, when such foreign financial institution or entity is acting as an intermediary), unless (i) in the case of a foreign financial institution, such institution enters into an agreement with the U.S. government to withhold on certain payments, and to collect and provide to the U.S. tax authorities substantial information regarding U.S. account holders of such institution (which includes certain equity and debt holders of such institution, as well as certain account holders that are foreign entities with U.S. owners), (ii) in the case of a non-financial foreign entity, such entity certifies that it does not have any substantial U.S. owners or provides the withholding agent with a certification (generally on an IRS Form W-8BEN-E) identifying the direct and indirect substantial U.S. owners of the entity, or (iii) the foreign financial institution or non-financial foreign entity otherwise qualifies for an exemption from these rules and provides appropriate documentation (such as an IRS Form W-8BEN-E). Under certain circumstances, a holder of our common stock might be eligible for refunds or credits of such taxes. Although withholding under FATCA would have applied to payments of gross proceeds from the taxable disposition of our common stock on or after January 1, 2019, proposed Treasury regulations eliminate FATCA withholding on payments of gross proceeds entirely. Taxpayers generally may rely on these proposed Treasury regulations until final Treasury regulations are issued. Intergovernmental agreements governing FATCA between the United States

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and certain other countries may modify the foregoing requirements for certain holders of our common stock. Prospective investors should consult their own tax advisors regarding FATCA and whether it may be relevant to the ownership and disposition of shares of our common stock.

Federal Estate Tax

Shares of our common stock beneficially owned by an individual who is not a citizen or resident of the United States (as defined for U.S. federal estate tax purposes) at the time of death will generally be includable in the decedent’s gross estate for U.S. federal estate tax purposes unless an applicable income tax treaty provides otherwise.

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UNDERWRITING (CONFLICTS OF INTEREST)

We are offering the shares of common stock described in this prospectus supplement and accompanying prospectus through Wells Fargo Securities, LLC (“Wells Fargo” or the “underwriter”) who is acting as the sole underwriter. We have entered into an underwriting agreement with Wells Fargo. Subject to the terms and conditions of the underwriting agreement, we have agreed to sell to the underwriter, and the underwriter has agreed to purchase, at the public offering price less the underwriting discounts and commissions set forth on the cover page of this prospectus supplement, the number of shares of common stock listed next to its name in the following table:

Name						Number of Shares
Wells Fargo Securities, LLC
Total

The underwriter is committed to purchase all the common stock offered by us if it purchases any shares. The underwriter proposes to offer the common stock directly to the public at the initial public offering price set forth on the cover page of this prospectus supplement and to certain dealers at that price less a concession not in excess of $ per share. After the initial offering of the shares to the public, if all of the shares of common stock are not sold at the initial public offering price, the underwriter may change the offering price and the other selling terms.

Discount

The underwriting fee is equal to the public offering price per share of common stock less the amount paid by the underwriter to us per share of common stock. The underwriting fee is $ per share. The following table shows the per share and total underwriting discounts and commissions to be paid to the underwriter.

Underwriting Fee

Per Share

Total

Expenses and Indemnification

We estimate that the total expenses of this offering, including registration, filing and listing fees, printing fees and legal and accounting expenses, but excluding the underwriting discounts and commissions, will be approximately $ .

We have agreed to indemnify the underwriter against certain liabilities, including liabilities under the Securities Act.

No Sales of Similar Securities

We have agreed that, without the prior written consent of the underwriter, we will not, during the period from and including the date of this prospectus supplement through and including the 60th day after the date of this prospectus supplement, (1) issue, offer, pledge, assign, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend or otherwise transfer or dispose of any shares of our common stock or other capital stock or any securities convertible into or exercisable or exchangeable for our common stock or other capital stock; (2) file or cause the filing of any registration statement under the Securities Act of 1933 with respect to any of our common stock or other capital stock or any securities convertible into or exercisable or exchangeable for any of our common stock or other capital stock; or enter into any swap or other agreement, arrangement, hedge or transaction that transfers to another, in whole or in part, directly or

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indirectly, any of the economic consequences of ownership of any of our common stock or other capital stock or any securities convertible into or exercisable or exchangeable for any of our common stock or other capital stock; whether any transaction described in clause (1) or (3) above is to be settled by delivery of common stock, other capital stock, other securities, in cash or otherwise, or publicly announce any intention to do any of the foregoing.

The foregoing sentence shall not apply to certain transactions, including:

(a) issuances of any shares of our common stock in accordance with this offering;

(b) issuances of shares, and options to purchase shares, of our common stock pursuant to stock option plans, stock purchase or other equity incentive plans or any dividend reinvestment plan described in this prospectus supplement and accompanying prospectus as those plans are in effect on the date of this prospectus supplement; and

(c) issuance of shares of our common stock upon the exercise of stock options issued under stock option or other equity incentive plans referred to in clause (b) above, as those plans are in effect on the date of this prospectus supplement, or upon the exercise of warrants or convertible securities outstanding on the date of this prospectus supplement, as those warrants and convertible securities are in effect on the date of this prospectus supplement.

Our directors and executive officers have entered into lock-up agreements with the underwriter prior to the commencement of this offering pursuant to which each of these directors and officers have agreed that, without the prior written consent of the underwriter, such director or officer will not, during the period commencing on and including the date of such director or officer’s lock-up agreement through and including the 60th day after the date of this prospectus supplement (the “Lock-Up Period”), offer, sell, contract to sell, pledge or otherwise dispose of, (or enter into any transaction which is designed to, or might reasonably be expected to, result in the disposition (whether by actual disposition or effective economic disposition due to cash settlement or otherwise) by such director or officer or any affiliate of such director or officer or any person in privity with such director or officer or any affiliate of such director or officer), directly or indirectly, including the filing (or participation in the filing) of a registration statement with the SEC in respect of, or establish or increase a put equivalent position or liquidate or decrease a call equivalent position within the meaning of Section 16 of the Exchange Act, and the rules and regulations of the SEC promulgated thereunder with respect to, any shares of our capital stock or any securities convertible into, or exercisable or exchangeable for such capital stock, or publicly announce an intention to effect any such transaction, other than:

(a) shares of common stock disposed of as bona fide gifts, by will, by intestate successor or pursuant to a so-called “living trust” or other revocable trust established to provide for the disposition of property on such director or officer’s death; provided that, in the case of any such transfer, it shall be a condition to such transfer that each transferee shall sign and deliver a lock-up letter; and provided, further, that in the case of such transfer, it shall be a condition to such transfer that (i) any such transfer shall not involve a disposition for value; and (ii) no filing under the Exchange Act or other public announcement shall be required or shall be voluntarily made during the Lock-Up Period; and

(b) shares of common stock deemed sold to us upon a cashless exercise of options or to satisfy tax withholding obligations in connection with the vesting of equity awards or otherwise deemed sold or transferred to us in connection with the issuance of shares pursuant to any employee benefit plans or other employee, executive or director compensation plan or our Direct Plan; provided, however, that in any such case the shares of capital stock issued upon exercise or settlement shall remain subject to the provisions of the lock-up letter and any Form 4 filed in accordance with Section 16 of the Exchange Act in connection with any such exercise or settlement will include a footnote disclosing that the filing relates to the exercise of a stock option or warrant or settlement of restricted stock units, as applicable (including a net exercise or a settlement for the purpose of satisfying tax withholding obligations, as applicable).

NYSE Symbol

Our common stock is listed on the NYSE under the symbol “TXNM”.

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Electronic Prospectus Delivery

The prospectus supplement and accompanying prospectus may be made available in electronic format on the web sites maintained by the underwriter, or selling group members, if any, participating in the offering. The underwriter may agree to allocate a number of shares to selling group members for sale to their online brokerage account holders. Internet distributions will be allocated by the underwriter and any selling group members that may make Internet distributions on the same basis as other allocations.

Price Stabilization, Short Positions and Penalty Bids

In connection with this offering, the underwriter may engage in stabilizing transactions, which involves making bids for, purchasing and selling shares of common stock in the open market for the purpose of preventing or retarding a decline in the market price of the common stock while this offering is in progress. These stabilizing transactions may include making short sales of common stock, which involves the sale by the underwriter of a greater number of shares of common stock than it is required to purchase in this offering, and purchasing shares of common stock on the open market to cover positions created by short sales.

The underwriter has advised us that, pursuant to Regulation M of the Securities Act, it may also engage in other activities that stabilize, maintain or otherwise affect the price of the common stock, including the imposition of penalty bids. This means that if the underwriter purchases common stock in the open market in stabilizing transactions or to cover short sales, the underwriter can require the selling group members that sold those shares as part of this offering to repay the underwriting discount received by them.

These activities may have the effect of raising or maintaining the market price of the common stock or preventing or retarding a decline in the market price of the common stock, and, as a result, the price of the common stock may be higher than the price that otherwise might exist in the open market. If the underwriter commences these activities, it may discontinue them at any time. The underwriter may carry out these transactions on the NYSE, in the over-the-counter market or otherwise.

Certain Relationships

In the ordinary course of its business, the underwriter and/or its affiliates have in the past performed, and may continue to perform, investment banking, broker dealer, lending, financial advisory or other services for us for which they have received, or may receive, separate fees. For example, as described below under “– Conflicts of Interest,” as of the date of this prospectus supplement an affiliate of Wells Fargo is a lender and agent under the TXNM 2026 Term Loan and our revolving credit facility.

The underwriter and its affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing, market making, brokerage and other financial and non-financial activities and services. In the ordinary course of its business, the underwriter and its affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers and such investment and securities activities may involve securities and/or instruments of the Company. The underwriter and its affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

Sales outside the United States

No action has been taken in any jurisdiction (except in the United States) that would permit a public offering of the common stock, or the possession, circulation or distribution of this prospectus supplement or accompanying prospectus or any other material relating to us or the common stock in any jurisdiction where action for that purpose is required. Accordingly, the common stock may not be offered or sold, directly or indirectly, and none of this prospectus supplement, the accompanying prospectus or any other offering material or advertisements

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in connection with the common stock may be distributed or published, in or from any country or jurisdiction except in compliance with any applicable rules and regulations of any such country or jurisdiction.

The underwriter may arrange to sell common shares offered hereby in certain jurisdictions outside the United States, either directly or through affiliates, where it is permitted to do so. Persons into whose possession this prospectus supplement comes are advised to inform themselves about and to observe any restrictions relating to the offering and the distribution of this prospectus supplement. This prospectus supplement does not constitute an offer to sell or a solicitation of an offer to buy any securities offered by this prospectus supplement in any jurisdiction in which such an offer or a solicitation is unlawful.

Notice to Prospective Investors in the European Economic Area

In relation to each Member State of the European Economic Area (each, a “Relevant State”), no shares of our common stock have been offered or will be offered pursuant to the offering to the public in that Relevant State prior to the publication of a prospectus in relation to such shares of our common stock which has been approved by the competent authority in that Relevant State or, where appropriate, approved in another Relevant State and notified to the competent authority in that Relevant State, all in accordance with the Prospectus Regulation, except that the shares of our common stock may be offered to the public in that Relevant State at any time:

(a)    to any qualified investor as defined under Article 2 of the Prospectus Regulation;

(b)    to fewer than 150 natural or legal persons (other than “qualified investors” as defined under Article 2 of the Prospectus Regulation), subject to obtaining the prior consent of the underwriter for any such offer; or

(c)    in any other circumstances falling within Article 1(4) of the Prospectus Regulation,

provided that no such offer of the shares of our common stock shall require us or any underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Regulation, supplement a prospectus pursuant to Article 23 of the Prospectus Regulation or publish an Annex IX document pursuant to Article 1(4) of the Prospectus Regulation and each person who initially acquires any shares of our common stock or to whom any offer is made will be deemed to have represented, warranted and agreed to and with the underwriter and us that it is a qualified investor within the meaning of Article 2 of the Prospectus Regulation

In the case of any shares of our common stock being offered to a financial intermediary as that term is used in Article 5(1) of the Prospectus Regulation, each financial intermediary will also be deemed to have represented, warranted and agreed that the Shares acquired by it in the offering have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer of any shares of our common stock to the public, other than their offer or resale in a Relevant State to qualified investors as so defined or in circumstances in which the prior consent of the underwriter has been obtained to each such proposed offer or resale.

We, the underwriter and their affiliates will rely upon the truth and accuracy of the foregoing representations, warranties and agreements.

For the purposes of this provision, the expression “an offer to the public” in relation to any shares of our common stock in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and any shares of our common stock to be offered so as to enable an investor to decide to purchase or subscribe for any shares of our common stock, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129.

Notice to Prospective Investors in the United Kingdom

No Shares have been offered or will be offered pursuant to the offering to the public in the United Kingdom, except that the shares of our common stock may be offered to the public in the United Kingdom at any time:

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(a)    where (i) the offer is conditional on the admission of the shares of our common stock to trading on the London Stock Exchange plc’s main market (in reliance on the exception in paragraph 6(a) of Schedule 1 of the POATR); or (ii) the shares of our common stock being offered are at the time of the offer already admitted to trading on the London Stock Exchange plc’s main market (in reliance on the exception in paragraph 6(b) of Schedule 1 of the POATR);

(b)    to any qualified investor as defined in paragraph 15 of Schedule 1 of the POATR;

(c)    to fewer than 150 persons (other than qualified investors as defined in paragraph 15 of Schedule 1 of the POATR, subject to obtaining the prior consent of the underwriter for any such offer; or

(d)    in any other circumstances falling within Part 1 of Schedule 1 of the POATR.

Each person who initially acquires any shares of our common stock or to whom any offer is made will be deemed to have represented, warranted and agreed to and with the underwriter and us that it is a qualified investor within the meaning of paragraph 15 of Schedule 1 of the POATR.

In the case of any shares of our common stock being offered to a financial intermediary as that term is used in paragraph 4 of regulation 7 of the POATR, each financial intermediary will also be deemed to have represented, warranted and agreed that the shares of our common stock acquired by it in the offering have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer of any Shares to the public, other than their offer or resale in the United Kingdom to qualified investors as so defined or in circumstances in which the prior consent of the underwriter has been obtained to each such proposed offer or resale.

We, the underwriter and their affiliates will rely upon the truth and accuracy of the foregoing representations, warranties and agreements.

For the purposes of this provision, the expression “an offer to the public” in relation to the shares of our common stock in the United Kingdom means the communication to any person which presents sufficient information on: (a) the shares of our common stock to be offered; and (b) the terms on which they are to be offered, to enable an investor to decide to buy or subscribe for any Shares and the expression “POATR” means the Public Offers and Admissions to Trading Regulations 2024.

Notice to Prospective Investors in Switzerland

Shares of our common stock may not be publicly offered, directly or indirectly, in Switzerland within the meaning of the Swiss Financial Services Act (“FinSA”) and no application has or will be made to admit shares of our common stock to trading on any trading venue (exchange or multi-lateral trading facility) in Switzerland.

Neither this prospectus supplement nor the accompanying prospectus or any other offering or marketing material relating to shares of our common stock or us constitutes a prospectus as such term is understood pursuant to the FinSA, and neither this prospectus supplement nor the accompanying prospectus or any other offering or marketing material relating to shares of our common stock or us may be distributed or otherwise made available in Switzerland.

Notice to Prospective Investors in Canada

Shares of our common stock may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of shares of our common stock must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

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Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement or the accompanying prospectus (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 Underwriting Conflicts (“NI 33-105”), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

Notice to Prospective Investors in Australia

No placement document, prospectus, product disclosure statement or other disclosure document has been lodged with the Australian Securities and Investments Commission (“ASIC”), in relation to the offering. This prospectus supplement and accompanying prospectus do not constitute a prospectus, product disclosure statement or other disclosure document under the Corporations Act 2001 (the “Corporations Act”), and do not purport to include the information required for a prospectus, product disclosure statement or other disclosure document under the Corporations Act.

Any offer in Australia of the shares of our common stock for sale may only be made to persons (the “Exempt Investors”) who are “sophisticated investors” (within the meaning of section 708(8) of the Corporations Act), “professional investors” (within the meaning of section 708(11) of the Corporations Act) or otherwise pursuant to one or more exemptions contained in section 708 of the Corporations Act or otherwise under the Corporations Act so that it is lawful to offer the shares of our common stock for sale without disclosure to investors under Chapter 6D of the Corporations Act.

Shares of our common stock must not be offered for sale in Australia in the period of 12 months after their issue or sale by us, except in circumstances where disclosure to investors under Chapter 6D of the Corporations Act would not be required pursuant to an exemption under section 708 of the Corporations Act or otherwise or where the offer is pursuant to a disclosure document which complies with Chapter 6D of the Corporations Act. Any person acquiring shares of our common stock must observe such Australian on-sale restrictions.

This prospectus supplement and accompanying prospectus contain general information only and do not take account of the investment objectives, financial situation or particular needs of any particular person. This prospectus supplement and accompanying prospectus do not contain any securities recommendations or financial product advice. Before making an investment decision, investors need to consider whether the information in this prospectus supplement and accompanying prospectus is appropriate to their needs, objectives and circumstances, and, if necessary, seek expert advice on those matters.

Conflicts of Interest

An affiliate of Wells Fargo Securities, LLC will receive more than 5% of the net offering proceeds as a result of our repayment of TXNM 2026 Term Loan. See “Use of Proceeds.” Accordingly, this offering is being made in compliance with the requirements of Rule 5121 of the Financial Industry Regulatory Authority, Inc. (“FINRA”). An appointment of a qualified independent underwriter is not necessary because the shares of common stock being offered have a “bona fide public market”, as defined in FINRA Rule 5121. Wells Fargo Securities, LLC will not confirm sales of the common stock to any account over which it exercises discretionary authority without the prior written approval of the customer.

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LEGAL MATTERS

The validity of the common stock offered hereby and certain other related legal matters will be passed upon for us by Leonard D. Sanchez, Esq., Associate General Counsel of TXNM, and Troutman Pepper Locke, LLP, and certain legal matters will be passed upon for the underwriter by Simpson Thacher & Bartlett LLP, New York, New York. As of August 25, 2026, Mr. Sanchez held 3,359 shares of TXNM common stock (pursuant to the vesting of restricted stock rights) and 1,348 restricted stock rights (which vest in equal annual installments over a three-year period from the respective grant date).

EXPERTS

The consolidated financial statements and schedules of TXNM Energy, Inc. as of December 31, 2025 and 2024, and for each of the years in the three-year period ended December 31, 2025, and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2025 have been incorporated by reference herein in reliance upon the report of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

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TXNM Energy, Inc.

Debt Securities

Common Stock

Preferred Stock

Warrants

Securities Purchase Contracts

Units

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf process, we may, from time to time, offer, issue and sell debt securities, shares of our common stock, shares of our preferred stock, warrants, securities purchase contracts or units, which we collectively refer to as the “securities”. We may offer and sell these securities in amounts, at prices and on terms determined at the time of the offering.

This prospectus describes some of the general terms that may apply to the securities. The specific terms of any securities to be offered will be described in supplements to this prospectus. The prospectus supplements also may add, update or change information contained in this prospectus. Any statement that we make in this prospectus will be modified or superseded by any inconsistent statement made by us in a prospectus supplement. This prospectus may not be used to sell securities unless accompanied by a prospectus supplement. You should carefully read this prospectus and the applicable prospectus supplement, together with the documents we incorporate by reference, before you make your investment decision.

We may sell the securities directly or to or through underwriters or dealers, and also to other purchasers or through agents or a combination of these methods. The names of any underwriters or agents participating in a sale of securities to you, and any applicable commissions or discounts, will be stated in an accompanying prospectus supplement. For general information about the distribution of securities offered, please see “Plan of Distribution” on page 22 of this prospectus.

Investing in our securities involves risks. See “Risk Factors” on page 4 and “Disclosure Regarding Forward Looking Statements” on page 4 for information on certain risks related to the purchase of any securities.

Our common stock is quoted on the New York Stock Exchange under the symbol “TXNM.”

Our executive office is located at 414 Silver Ave. SW, Albuquerque, New Mexico 87102, and our telephone number is (505) 241-2700.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is February 28, 2025.

TABLE OF CONTENTS

Prospectus

Page

About this Prospectus			1
Where You Can Find More Information			3
TXNM Energy, Inc.			4
Risk Factors			4
Disclosure Regarding Forward-Looking Statements			5
Use of Proceeds			5
Description of Debt Securities			6
Description of Common Stock and Preferred Stock			16
Description of Warrants			19
Description of Securities Purchase Contracts			22
Description of Units			23
Plan of Distribution			24
Legal Matters			26
Experts			26

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process.

This prospectus provides you with a general description of the securities we may offer. Each time we offer and sell the securities, we will describe in a supplement to this prospectus the specific terms of that offering. The applicable prospectus supplement also may add, update or change information in this prospectus. Please carefully read both this prospectus and the applicable prospectus supplement, together with the documents that are incorporated by reference herein that are described under “Where You Can Find More Information,” before investing in the securities. In particular, you should carefully consider the risks and uncertainties described under the section titled “Risk Factors” or otherwise included in any applicable prospectus supplement or incorporated by reference in this prospectus before you decide whether to purchase the securities.

Unless otherwise indicated or unless the context otherwise requires, all references in this prospectus and any accompanying prospectus supplement to “TXNM,” “TXNM Energy,” “we,” “our” and “us” refer to TXNM Energy, Inc. and its subsidiaries. Unless otherwise indicated, financial information included or incorporated by reference herein and in any accompanying prospectus supplement is for TXNM Energy, Inc. and its subsidiaries on a consolidated basis.

This prospectus contains summaries of certain provisions contained in some of the documents described in this prospectus. Please refer to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of the documents referred to in this prospectus have been filed, or will be filed or incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under “Where You Can Find More Information.”

Pursuant to the registration statement of which this prospectus is a part, we may offer, issue and sell securities as set forth on the cover page of this prospectus. Because we are a “well-known seasoned issuer,” as defined in Rule 405 of the Securities Act of 1933, as amended, which we refer to as the “Securities Act,” we may add to and offer additional securities, including securities held by security holders, by filing a prospectus supplement with the SEC at the time of the offer.

You should rely only on the information contained or incorporated by reference in this prospectus, any applicable prospectus supplements and any free writing prospectus prepared by or on behalf of us. We have

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not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not making an offer to sell these.

Securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus, any applicable prospectus supplement, any free writing prospectuses and the documents incorporated by reference is accurate only as of the respective dates of those documents in which the information is contained. Our business, financial condition, results of operations and prospects may have changed since those dates.

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WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports and other information with the SEC. You may read and copy these documents at the SEC’s Public Reference Room at 100 F Street, N.E., Room 1580, Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information about the Public Reference Room. The SEC also maintains an Internet website that contains reports, proxy and information statements and other information regarding registrants that file electronically with the SEC. The address of the site is www.sec.gov.

Our Internet address is www.txnmenergy.com. The contents of the website are not a part of the registration statement of which this prospectus is a part. Our filings with the SEC, including annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and amendments to those reports, filed or furnished pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, which we refer to as the “Exchange Act”, are accessible free of charge at www.txnmenergy.com as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC. These reports are also available upon request in print from us free of charge.

We are “incorporating by reference” in this prospectus information we file with the SEC, which means that we are disclosing important information to you by referring you to those documents. Our combined filings with the SEC present separate filings by TXNM, Public Service Company of New Mexico (“PNM”) and Texas-New Mexico Power Company (“TNMP”). Information contained therein relating to an individual registrant is filed by that registrant on its own behalf and each registrant makes no representation as to information relating to other registrants. The information we incorporate by reference is considered to be part of this prospectus, unless it is updated or superseded by the information contained in this prospectus or the information we file subsequently with the SEC that is incorporated by reference in this prospectus or a prospectus supplement. We are incorporating by reference the following documents that we have filed with the SEC (except those portions of filings that relate to PNM or TNMP as separate registrants), other than any information in these documents that is deemed not to be “filed” with the SEC:

•our Annual Report on Form 10-K for the year ended December 31, 2024, filed with the SEC on February 28. 2025;

•our Current Reports on Form 8-K, filed with the SEC on January 22, 2025, February 14, 2025, and February 27, 2025;

•the description of our common stock contained in our Exhibit 4.1 to our Annual Report on Form 10-K for the fiscal year ended December 31, 2024, filed with the SEC on February 28, 2025, including any amendments or reports filed for the purpose of updating such description.

We also incorporate by reference into this prospectus any filings we make with the SEC (excluding information furnished under Item 2.02 or 7.01 of Current Reports on Form 8-K) under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act, after the initial filing of the registration statement that contains this prospectus.

You may obtain without charge a copy of any of the documents we incorporate by reference, except for exhibits to such documents which are not specifically incorporated by reference into such documents, by contacting us at TXNM Energy, Inc., 414 Silver Ave. SW, Albuquerque, New Mexico, 87102-3289, Attention: Shareholder Services. You may also telephone your request at (505) 241-2868.

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TXNM ENERGY, INC.

TXNM is a holding company with two regulated electric utilities, PNM and TNMP, serving approximately 834,000 residential, commercial, and industrial customers in New Mexico and Texas. TXNM was incorporated in the State of New Mexico in 2000 and its common stock trades on the New York Stock Exchange under the symbol TXNM.

TXNM’s vision is to create a clean and bright energy future while fulfilling its purpose to work together with customers and communities to meet their energy needs. TXNM’s core values of Safety, Caring and Integrity are the foundation for the Company’s business objectives focused on safety excellence and customer satisfaction, including reliability. To reach these objectives, the Company is committed to:

•Preparing our workforce with the knowledge and skills to thrive in a customer-focused world;

•Purposefully delivering an intentional customer experience that exceeds our evolving customer and stakeholder expectations;

•Enabling an environmentally sustainable future and deploying technologically advanced solutions that empower and benefit customers;

•Demonstrating the relationship between customer excellence and our dedicated focus on financial strength;

Meeting the business objectives above will drive key financial results:

•Earning authorized returns on regulated businesses;

•Delivering at or above industry-average long-term earnings growth, with a dividend payout ratio between 50 and 60 percent of earnings; and

•Maintaining investment grade credit ratings.

The Company believes that maintaining strong and modern electric infrastructure is critical to ensuring reliability and supporting economic growth. PNM and TNMP strive to balance service affordability with infrastructure investment to maintain a high level of electric reliability and to deliver a safe and superior customer experience. Both PNM and TNMP seek cost recovery for their investments through general rate cases, periodic cost of service filings, and various rate riders.

Our executive office is located at 414 Silver Ave. SW, Albuquerque, New Mexico 87102-3289, and our telephone number is (505) 241-2700.

RISK FACTORS

Investing in the securities involves risk. Please carefully consider the specific risks set forth under the section entitled “Risk Factors” in our most recent Annual Report on Form 10-K, together with all of the other information included in this prospectus and any prospectus supplement and any other information that we have incorporated by reference, including annual, quarterly and other reports filed with the SEC subsequent to the date hereof, which are all incorporated by reference in this prospectus, and in the applicable prospectus supplement. Before making an investment decision, you should carefully consider these risks as well as other information contained or incorporated by reference in this prospectus or the applicable supplement to this prospectus. The risks and uncertainties described are not the only ones facing us. Additional risks and uncertainties not presently known to us or that we currently deem immaterial also may impair our business operations, financial results and the value of our securities.

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DISCLOSURE REGARDING FORWARD LOOKING STATEMENTS

This prospectus, any accompanying prospectus supplement, other offering materials and the documents incorporated by reference herein and therein contain forward-looking statements within the meaning of Section 27A of the Securities Act, as amended, and Section 21E of the Exchange Act. These forward-looking statements relate to future events or our expectations, projections, estimates, intentions, goals, targets, and strategies and are made pursuant to the Private Securities Litigation Reform Act of 1995. You are cautioned that all forward-looking statements are based upon current expectations and estimates, and we assume no obligation to update this information. You generally can identify these statements by the use of words such as “outlook,” “potential,” “continue,” “may,” “seek,” “approximately,” “predict,” “believe,” “expect,” “plan,” “intend,” “estimate” or “anticipate” and similar expressions or the negative versions of these words or comparable words, as well as future or conditional verbs such as “will,” “should,” “would,” “likely” and “could.” These statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those included in the forward-looking statements.

Because actual results may differ materially from those expressed or implied by these forward-looking statements, we caution you not to place undue reliance on these statements. Our business, financial condition, cash flow, and operating results are influenced by many factors, which are often beyond our control, that can cause actual results to differ from those expressed or implied by the forward-looking statements.

Important risk factors that could cause our results to differ materially from those expressed in the forward-looking statements are listed under “Risk Factors” in a prospectus supplement and may also be found in our periodic reports filed with the SEC at www.sec.gov.

USE OF PROCEEDS

Each prospectus supplement will describe the uses of the proceeds from our issuances and sales of securities offered by that prospectus supplement.

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DESCRIPTION OF DEBT SECURITIES

General

The following description sets forth certain general terms and provisions of our debt securities. When we offer our debt securities in the future, a prospectus supplement will explain the particular terms of those debt securities and the extent to which any of these general provisions will not apply. You should read this prospectus and any applicable prospectus supplement before you make any investment decision. We may issue one or more series of debt securities directly to the public or as part of a purchase unit from time to time. We may also sell hybrid or novel securities now existing or developed in the future that combine certain features of the debt securities described in this prospectus.

The debt securities will be our direct unsecured general obligations. We may issue the debt securities from time to time in one or more series under an indenture dated as of March 15, 2005 between us and U.S. Bank Trust Company, National Association (ultimate successor as trustee to JPMorgan Chase Bank, N.A.), as trustee (the ‘‘Trustee’’). This indenture, as previously amended and supplemented and as it may be further amended and supplemented from time to time, is referred to in this prospectus as the ‘‘Indenture.’’

We have summarized selected provisions of the Indenture below. You should read this summary together with the Indenture, any supplemental indentures or other documents establishing the debt securities for a complete understanding of the provisions that may be important to you. The following description of the debt securities and the Indenture is qualified by reference to the Indenture, which is incorporated by reference as an exhibit to the registration statement of which this prospectus is a part. References to certain sections in parentheses below are references to sections of the Indenture. Whenever particular provisions or defined terms in the Indenture are referred to under this ‘‘Description of Debt Securities,’’ such provisions or defined terms are incorporated by reference herein. The Indenture is qualified under the Trust Indenture Act of 1939. You should refer to the Trust Indenture Act of 1939 for provisions that apply to the debt securities.

There is no requirement under the Indenture that our future issuances of debt securities be issued exclusively under the Indenture and we will be free to employ other indentures or documentation containing provisions different from those included in the Indenture or applicable to one or more issuances of debt securities in connection with future issuances of other debt securities. Nonetheless, the debt securities registered under the registration statement of which this prospectus is a part will only be issued either pursuant to the Indenture or pursuant to an indenture (or a form thereof) that is filed with the SEC in connection with the offering of the debt securities.

The Indenture provides that the applicable debt securities will be issued in one or more series, may be issued at various times, may have differing maturity dates and may bear interest at differing rates. We need not issue all debt securities of one series at the same time and, unless otherwise provided, we may reopen a series, without the consent of the holders of the debt securities of that series for issuances of additional debt securities of that series. Unless otherwise described in the applicable prospectus supplement, the Indenture does not limit the aggregate amount of debt, including secured debt, we or our subsidiaries may incur.

The Indenture does not currently contain any restriction on the payment of dividends or any financial covenants. However, the supplemental indenture for any series of debt securities may contain such restrictions. The prospectus supplement related to such debt securities will describe such restrictions and the protections, if any, that such restrictions provide the holders of the debt securities in the event of a highly leveraged transaction involving us that may adversely affect the holders of the debt securities.

Ranking

The debt securities will be our direct unsecured general obligations and will rank equally with all of our other unsubordinated debt. As of December 31, 2024, TXNM, exclusive of its subsidiaries, had $555 million of outstanding short-term and long-term debt that would have ranked equally with the debt securities.

We are a holding company and derive substantially all of our income from our operating subsidiaries. As a result, our cash flows and consequent ability to service our debt, including the debt securities, are dependent upon the

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earnings of our subsidiaries and distribution of those earnings to us and other payments or distributions of funds by our subsidiaries to us, including payments of principal and interest under intercompany indebtedness. Our operating subsidiaries are separate and distinct legal entities and will have no obligation, contingent or otherwise, to pay any dividends or make any other distributions (except for payments required pursuant to the terms of intercompany indebtedness) to us or to otherwise pay amounts due with respect to the debt securities or to make specific funds available for such payments. Various financing arrangements, charter provisions and regulatory requirements may impose certain restrictions on the ability of our subsidiaries to transfer funds to us in the form of cash dividends, loans or advances. The debt securities will be effectively subordinated to the claims of all creditors, including trade creditors and tort claimants, of our subsidiaries. In the event of the bankruptcy, insolvency, liquidation or reorganization of the business of one of our subsidiaries, creditors of that subsidiary would generally have the right to be paid in full before any distribution is made to us or the holders of the debt securities. As of December 31, 2024, our subsidiary PNM had $11.5 million aggregate stated value of cumulative preferred stock outstanding and $2,834 million aggregate principal amount of short-term and long-term debt outstanding, $340.7 million of which was secured. As of December 31, 2024, our subsidiary TNMP had $1,610 million aggregate principal amount of secured short-term and long-term debt outstanding.

The Indenture provides that payment of principal, premium and interest on any debt security issued under the Indenture shall be made solely from the assets of TXNM and not from any assets of utility subsidiaries.

Provisions of a Particular Series

The prospectus supplement relating to any series of debt securities being offered will include specific terms relating to that offering. These terms will include any of the following terms that apply to that series:

•the title of the debt securities;

•the total principal amount of the debt securities;

•the person or persons to whom interest payments are made, if other than the registered holder;

•the date or dates on which the principal of the debt securities will be payable, how the dates will be determined and whether the stated maturity may be extended;

•the rate or rates at which the debt securities will bear interest, if any, and how the rate or rates will be determined;

•the date or dates from which interest on the debt securities will accrue, the interest payment dates on which interest will be paid, and the record dates for the interest payments;

•the right, if any, to extend the interest payment periods for the debt securities and the duration of the extension;

•the place or places at which or methods by which payments will be made;

•whether we have the option to redeem the debt securities and, if so, the terms of our redemption option;

•any sinking fund or other provisions or options held by holders of the debt securities that would obligate us to repurchase or otherwise redeem the debt securities;

•if the debt securities will be issued in denominations other than $1,000 and integral multiples thereof;

•any index or formula used for determining principal, premium or interest;

•any collateral, security, assurance or guarantee applicable to a series of debt securities;

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•the currency or currencies in which payments will be made if other than United States dollars, and the manner of determining the equivalent of those amounts in United States dollars;

•if payments may be made on any of the debt securities, at our election or at the holder’s election, in a currency or currencies other than that in which the debt securities are stated to be payable, then the currency or currencies in which those payments may be made, the terms and conditions of the election and the manner of determining those amounts;

•the portion of the principal payable upon acceleration of maturity, if other than the entire principal;

•if the principal payable on the maturity date will not be determinable on one or more dates prior to the maturity date, the amount which will be deemed to be such principal amount as of any such date or the manner of determining such amount;

•whether the provisions described below under ‘‘Discharge, Defeasance and Covenant Defeasance’’ will apply to the debt securities;

•whether the debt securities will be issuable as global securities and, if so, the securities depositary;

•any changes or additions to the events of default under the Indenture or changes or additions to our covenants under the Indenture; and

•any other terms of the debt securities not inconsistent with the terms of the Indenture.

(See Section 3.01)

All debt securities of any one series will be substantially identical except as to denomination and except as may otherwise be determined in the manner provided for in the Indenture. (See Section 3.01)

Debt securities may be issued and sold at a substantial discount below their stated principal amount. If applicable, the prospectus supplement will describe any special United States federal income tax consequences and other considerations which apply to senior debt securities issued at a discount or to any securities denominated or payable in a foreign currency or currency unit.

Redemption

We will set forth any terms for the redemption of any debt securities in the applicable prospectus supplement. Unless we indicate differently in the applicable prospectus supplement, the debt securities will be redeemable upon notice by mail to the holders between 30 and 60 days prior to the redemption date. If less than all of the debt securities of any series are to be redeemed, the Trustee will select the debt securities to be redeemed from the outstanding debt securities of such series or tranche, not previously called for redemption. In the absence of any provision for selection, the Trustee will choose a method of random selection as it deems fair and appropriate. (See Sections 11.03 and 11.04)

The debt securities will cease to bear interest on the redemption date assuming we redeem them. We will pay the redemption price and any accrued interest once the debt securities are surrendered for redemption. If only part of a debt security is redeemed, the Trustee will deliver to you a new debt security of the same series for the remaining portion without charge. (See Section 11.07)

We may make any redemption, at our option, conditional upon the receipt by the paying agent or agents, on or prior to the date fixed for redemption, of money sufficient to pay the redemption price. If the paying agent or agents have not received the money by the date fixed for redemption, we will not be required to redeem the debt securities. (See Section 11.04)

Payment

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Except as may be provided in the applicable prospectus supplement, interest, if any, on each debt security payable on each interest payment date will be paid to the person in whose name the debt security is registered as of the close of business on the regular record date for the interest payment date. If there has been a default in the payment of interest on any debt security, the defaulted interest may be paid to the holder of that debt security as of the close of business on a date to be fixed by the Trustee, which will be between 10 and 15 days prior to the date we proposed for payment of the defaulted interest, and not less than 10 days after receipt by the Trustee of the notice of the proposed payment. The defaulted interest may also be paid in any other manner permitted by any securities exchange on which that debt security may be listed, if the Trustee finds it practicable. (See Section 3.07)

Registration of Transfer and Exchange

Unless otherwise specified in the prospectus supplement applicable to any series of debt securities, subject to any limitations on the transfer of global securities, the transfer of the debt securities may be registered, and the debt securities may be exchanged for other debt securities of the same series, of authorized denominations and with the same terms and principal amount, at the corporate trust office of the Trustee. We may change the place for registration of transfer and exchange of the debt securities and may designate additional places for registration and exchange. Unless otherwise provided in the prospectus supplement applicable to any series of debt securities, no service charge will be made for any transfer or exchange of the debt securities. However, we may require payment to cover any tax or other governmental charge that may be imposed. We will not be required to execute or to provide for the registration of transfer of, or the exchange of:

•any debt security during a period of 15 days prior to giving any notice of redemption; or

•any debt security selected for redemption except the unredeemed portion of any debt security being redeemed in part.

(See Section 3.05)

Restrictions on Mergers and Sale of Assets

Under the terms of the Indenture, we may not consolidate with or merge into any other entity or convey, transfer or lease our properties and assets substantially as an entirety to any entity or individual, unless:

•the surviving or successor entity is organized and validly existing under the laws of the United States, any state thereof or the District of Columbia and it expressly assumes our obligations on all debt securities and under the Indenture;

•immediately after giving effect to the transaction, no event of default and no event which, after notice or lapse of time or both, would become an event of default shall have occurred and be continuing; and

•we deliver to the Trustee an officers’ certificate and an opinion of counsel as to compliance with the foregoing.

(See Section 8.01)

Discharge, Defeasance and Covenant Defeasance

The Indenture provides that we may be:

•discharged from our obligations, with certain limited exceptions, with respect to any particular series of debt securities, as described in the Indenture, such a discharge being called a ‘‘defeasance’’ in this prospectus; and

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•released from our obligations under certain restrictive covenants especially established with respect to any particular series of debt securities, including the covenants described above under ‘‘Restrictions on Mergers and Sale of Assets’’ and any additional covenants set forth in the applicable prospectus supplement, such a release being called a ‘‘covenant defeasance’’ in this prospectus.

(See Section 13.02 and 13.03)

We must satisfy certain conditions to effect a defeasance or covenant defeasance. Those conditions include the irrevocable deposit with the Trustee, in trust, of money or government obligations which through their scheduled payments of principal and interest would provide sufficient money to pay the principal and any premium and interest on those debt securities on the maturity dates of those payments or upon redemption. In addition, we will be required to deliver to the Trustee an opinion of counsel to the effect that the deposit and related defeasance or covenant defeasance will not cause the holders of the applicable series of debt securities to recognize gain or loss for federal income tax purposes, and that such holders will be subject to federal income tax on the same amount, in the same manner and at the same times as would be the case if such deposit and related defeasance or covenant defeasance were not to occur. In the case of a defeasance, that opinion of counsel must be based upon a ruling from the Internal Revenue Service or a change in federal income tax law. (See Section 13.04)

Modification of the Indenture

We and the Trustee may enter into one or more supplemental indentures without the consent of any holder of the debt securities for certain specified purposes, including:

•to evidence the assumption by any permitted successor of our covenants in the Indenture and in the debt securities;

•to add to our existing covenants or to surrender any of our rights or powers under the Indenture;

•to add additional events of default;

•to add to or change any of the provisions to such extent necessary for the issuance of debt securities in bearer form, registrable or not registrable as to principal, and with or without interest coupons, or to permit or facilitate the issuance of debt securities in uncertificated form;

•to change, eliminate, or add any provision to the Indenture; provided, however, if the change, elimination, or addition will adversely affect the interests of the holders of the debt securities of any particular series in any material respect, that change, elimination, or addition will become effective only:

•when the consent of the holders of a majority in aggregate principal amount of the debt securities of that series has been obtained in accordance with the Indenture; or

•when no debt securities of the affected series remain outstanding under the Indenture;

•to secure the debt securities;

•to establish the form or terms of the debt securities of any other series as permitted by the Indenture;

•to evidence and provide for the acceptance of appointment of a successor trustee;

•to provide for or facilitate the administration of the trust by more than one trustee; or

•to cure any ambiguity or inconsistency or to make any other provisions with respect to matters and questions arising under the Indenture; provided that the action will not adversely affect the interests of the holders of the debt securities of any particular series in any material respect.

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(See Section 9.01)

If the Trust Indenture Act of 1939 is amended after the date of the Indenture to require changes to the Indenture, the Indenture will be deemed to be amended so as to conform to that amendment of the Trust Indenture Act of 1939. We and the Trustee may, without the consent of any of the holders, enter into one or more supplemental indentures to evidence that amendment. (See Section 9.01)

The consent of the holders of a majority in aggregate principal amount of the debt securities of all series then outstanding, considered as one class, is required for all other modifications to the Indenture. However, if less than all of the series of debt securities outstanding are directly affected by a proposed supplemental indenture, then only the consent of the holders of a majority in aggregate principal amount of the outstanding debt securities of all series that are directly affected will be required. No amendment or modification may:

•change the stated maturity of the principal of, or any installment of principal of or interest on, any debt security, or reduce the principal amount of any debt security or its rate of interest or change the method of calculating the interest rate or reduce any premium payable upon redemption, or reduce the amount of the principal of any debt security which would be due and payable upon a declaration of acceleration of the maturity thereof, or change the currency in which payments are made, or impair the right to institute suit for the enforcement of any payment on or after the date that any principal or interest is due and payable on any debt security, without the consent of the holder;

•reduce the percentage in principal amount of the outstanding debt security of any particular series the consent of which is required for any supplemental indenture or any waiver of compliance with a provision of the Indenture or any default thereunder and its consequences, or reduce the requirements for quorum or voting, without the consent of all the holders of the series; or

•modify certain provisions of the Indenture relating to supplemental indentures, waivers of certain covenants and waivers of past defaults with respect to the debt securities of any particular series, without, in each case, the consent of the holder of each outstanding debt security affected thereby.

(See Section 9.02)

A supplemental indenture which changes the Indenture solely for the benefit of one or more particular series of debt securities, or modifies the rights of the holders of the debt securities of one or more series, will not affect the rights under the Indenture of the holders of the debt securities of any other series. (See Section 9.02)

The Indenture provides that the debt securities owned by us or anyone else required to make payment on the debt securities will be disregarded and considered not to be outstanding in determining whether the required holders have given a request or consent. (See Section 1.01)

We may fix in advance a record date to determine the required number of holders entitled to give any request, demand, authorization, direction, notice, consent, waiver or other such ‘‘act’’ or action of the holders, in certain situations. If the record date is fixed, the holders of the outstanding debt securities of the relevant series on that record date, and no other holders, will be entitled to take or revoke the relevant action, whether or not those holders remain holders after that record date. No action, however, will be effective unless taken on or prior to the applicable expiration date by holders of the requisite principal amount of the outstanding debt securities of that series on that record date. Any request, demand, authorization, direction, notice, consent, election, waiver or other act of a holder will bind every future holder of the same debt securities and the holder of every debt security issued upon the registration of transfer of or in exchange of those debt securities. A transferee will be bound by our acts or those of the Trustee taken in reliance thereon, whether or not notation of that action is made upon that debt security. (See Section 1.04)

Events of Default

‘‘Event of default’’ when used in the Indenture with respect to any particular series of debt securities, means any of the following:

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•failure to pay interest on any debt security of the applicable series for 60 days after it is due;

•failure to pay the principal of or premium on any debt security of the applicable series when due (whether at maturity or upon earlier redemption);

•failure to pay the deposit of any sinking fund payment, when and as due by the terms of the applicable series;

•failure to perform any other covenant in the Indenture, other than a covenant that does not relate to that series of debt securities, that continues for 90 days after we receive written notice from the Trustee, or we and the Trustee receive a written notice from the holders of a majority in principal amount of the debt securities of such series; however, the Trustee or the Trustee and such holders, as applicable, can agree to an extension of the 90-day period and this extension will be automatic if we are diligently pursuing action to correct the default;

•certain events related to our bankruptcy, insolvency or reorganization; or

•any other event of default provided with respect to the debt securities of that series.

(See Section 5.01)

Remedies

Acceleration of Maturity

If an event of default with respect to any one series of debt securities occurs and continues, either the Trustee or the holders of a majority in principal amount of the outstanding debt securities of that series may declare the principal amount of all the debt securities of that series to be due and payable immediately. However, if the event of default is applicable to more than one series of debt securities, the Trustee or the holders of a majority in principal amount of all the outstanding debt securities of all series, considered as one class, and not the holders of any one series, may make a declaration of acceleration. (See Section 5.02)

At any time after a declaration of acceleration has been made and before a judgment or decree for payment of the money due has been obtained by the Trustee, the event of default giving rise to the declaration of acceleration will be considered waived, and the declaration and its consequences will be automatically rescinded and annulled if:

•we have paid or deposited with the Trustee a sum sufficient to pay:

•all overdue interest on all the debt securities of the series;

•the principal of and premium, if any, on any debt securities of the series which have otherwise become due and interest, if any, that is currently due;

•interest, if any, on overdue interest (to the extent lawful); and

•all amounts due to the Trustee under the Indenture; and

•any other event of default with respect to the debt securities of that series has been cured or waived as provided in the Indenture.

(See Section 5.02)

The holders of a majority in principal amount of the outstanding debt securities of any particular series may on behalf of the holders of all the debt securities of that series waive any past default under the Indenture with respect to that series and its consequences, except a default:

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•in the payment of the principal of or any premium or interest on any debt security of that series, or

•in respect of a covenant or provision of the Indenture which cannot be modified or amended by supplemental indenture without the consent of the holder of each outstanding debt security of the series affected.

However, if a default occurs and continues with respect to more than one series of debt securities, the holders of a majority in aggregate principal amount of the outstanding debt securities of all such series, considered as one class, has the right to waive the default, and not the holders of the debt securities of any one such series. Upon any waiver, the default ceases to exist, and any and all events of default arising therefrom is deemed to have been cured, for every purpose of the Indenture; but no waiver will extend to any subsequent or other default or impair any right consequent thereon.

(See Section 5.13)

Right to Direct Proceedings

If an event of default with respect to any particular series of debt securities occurs and continues, the holders of a majority in principal amount of the outstanding debt securities of that series have the right to direct the time, method and place of conducting any proceeding for any remedy available to the Trustee, or exercising any trust or power conferred on the Trustee, with respect to the debt securities of that series. However, if an event of default occurs and continues with respect to more than one series of debt securities, the holders of a majority in aggregate principal amount of the outstanding debt securities of all such series, considered as one class, have the right to make the direction, and not the holders of the debt securities of any one of such series. In either case, the Indenture further provides that:

•such direction will not be in conflict with any rule of law or with the Indenture;

•the Trustee may take any other action deemed proper by the Trustee and not inconsistent with such direction, and

•subject to the provisions of the Indenture the Trustee will have the right to decline to follow any direction if the Trustee in good faith determines that the proceeding so directed would involve the Trustee in personal liability.

(See Section 5.12)

Limitation on Right to Institute Proceedings

No holder of debt securities of any particular series will have any right to institute any proceeding, judicial or otherwise, with respect to the Indenture, or for the appointment of a receiver or Trustee, or for any other remedy under the Indenture, unless:

•the holder has previously given to the Trustee written notice of a continuing event of default;

•the holders of a majority in aggregate principal amount of the outstanding debt securities of all series in respect of which an event of default has occurred and is continuing, considered as one class, have made a written request to the Trustee;

•such holder or holders have offered reasonable indemnity to the Trustee to institute proceedings; and

•the Trustee has failed to institute any proceeding for 60 days after notice and has not received any direction inconsistent with the written request of the holders during that period.

(See Section 5.07)

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No Impairment of Right to Receive Payment

The limitations on the right to institute proceedings, however, do not apply to a suit by a holder of a debt security for payment of the principal of or premium, if any, or interest if any, on that debt security on or after the applicable due date. (See Section 5.08)

Annual Notice to Trustee

We will provide to the Trustee an annual statement by an appropriate officer as to whether we are in default in the performance and observance of any of the terms, provisions and conditions of the Indenture. (See Section 10.04)

Notices

Notices to holders of the debt securities will be given by mail to the holders at the addresses that appear in the security register. (See Section 1.06)

Title

We, the Trustee, and any of our agents or the agents of the Trustee, may treat the person in whose name the debt securities are registered as the absolute owner thereof, whether or not such debt securities may be overdue, for the purpose of making payments and for all other purposes irrespective of notice to the contrary. (See Section 3.08)

Governing Law

The Indenture and the debt securities will be governed by, and construed in accordance with, the laws of the State of New York. (See Section 1.12)

Regarding the Trustee

The Trustee is U.S. Bank Trust Company, National Association (ultimate successor to JPMorgan Chase Bank, N.A.). In addition to acting as Trustee, U.S. Bank Trust Company, National Association and its affiliates act, and may act, as Trustee under our and/or our affiliates’ other various indentures and trusts. We and our affiliates also maintain credit and liquidity facilities and conduct other banking transactions with affiliates of the Trustee in the ordinary course of our businesses.

The Trustee may resign at any time by giving us written notice or be removed at any time by an act of the holders of a majority in principal amount of any particular series of debt securities then outstanding delivered to the Trustee and us. In addition, provided that no event of default has occurred or is continuing, we may appoint a new trustee upon delivering to the Trustee a resolution of our board of directors appointing a successor trustee and the successor’s acceptance of our appointment. In this case, the Trustee will be deemed to have resigned and the successor will be deemed to have been appointed as trustee in accordance with the Indenture. In any event, the resignation or removal of the Trustee, and no appointment of a successor trustee, will be effective until the acceptance of appointment by a successor trustee. (See Section 6.10)

The Trustee will perform only those duties that are specifically set forth in the Indenture unless an event of default under the Indenture occurs and continues. In case an event of default occurs and continues, the Trustee will exercise the same degree of care and skill as a prudent individual would exercise in the conduct of his or her own affairs. (See Section 6.01)

Book-Entry Issuance

Unless otherwise provided in a prospectus supplement, we will issue debt securities of each series in the form of one or more fully registered global securities. The global securities will be deposited with the Trustee under the Indenture as custodian for the depositary, which will be The Depository Trust Company or another depositary identified in a prospectus supplement, and registered in the name of the depositary or its nominee.

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Unless and until it is exchanged in whole or in part for the individual debt securities it represents, a global security may not be transferred except as a whole:

•by the applicable depositary to a nominee of the depositary;

•by any nominee of the depositary to the depositary or another nominee; or

•by the depositary or any nominee to a successor depositary or any nominee of the successor.

Investors may hold their beneficial interests in the global securities directly through the depositary if they have an account with the depositary or indirectly through organizations that have accounts with the depositary.

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DESCRIPTION OF COMMON STOCK AND PREFERRED STOCK

The following summary of the material terms of the common stock and preferred stock of TXNM Energy, Inc. (“we” or “our”) does not purport to be complete and is subject to and qualified in its entirety by reference to our articles of incorporation, as amended (our “articles of incorporation”), and by-laws, as amended (our “by-laws”), each of which is incorporated by reference as exhibits to our Annual Report on Form 10-K for the year ended December 31, 2024, filed with the SEC on February 28, 2025. For a more complete understanding of our common stock and preferred stock, we encourage you to read carefully our articles of incorporation and by-laws, each as may be amended, and the applicable provisions of the New Mexico Business Corporation Act and the New Mexico Public Utility Act and other applicable provisions of the laws of the state of New Mexico.

General

Our authorized capital stock consists of 200,000,000 shares of common stock, no par value and 10,000,000 shares of preferred stock, no par value, of which 500,000 shares have been designated Convertible Preferred Stock, Series A, which we refer to in this prospectus as “Series A Preferred Stock”. Each share of Series A Preferred Stock is convertible at the option of the holder at any time into 10 shares of common stock, subject to certain anti-dilution adjustments. As of December 31, 2024, 92,659,335 shares of our common stock and no shares of our Series A Preferred Stock were outstanding.

Dividend Rights with Respect to Our Common Stock and Series A Preferred Stock

After giving effect to any prior rights of our Series A Preferred Stock, and any other series of preferred stock that should become outstanding, we will pay dividends on our common stock as determined by our Board of Directors (the “Board”) out of legally available funds. Our ability to pay dividends depends primarily upon the ability of our subsidiaries to pay dividends or otherwise transfer funds to us. Various financing arrangements, charter provisions and regulatory requirements may impose certain restrictions on the ability of our subsidiaries to transfer funds to us in the form of cash dividends, loans or advances.

Unless waived by the holders of at least two-thirds of the number of then outstanding shares of Series A Preferred Stock, no dividend on our common stock shall be declared unless a dividend on the Series A Preferred Stock is declared and paid at the same time in an amount equal to the dividend that would be received by a holder of the number of shares (including fractional shares) of common stock into which such Series A Preferred Stock is convertible on the record date for such dividend.

Voting Rights with Respect to Our Common Stock and Series A Preferred Stock

Holders of common stock are entitled to one vote for each share held by them on all matters submitted to our shareholders. Holders of our common stock do not have cumulative voting rights in the election of directors. The New Mexico Business Corporation Act and our articles of incorporation and by-laws generally require the affirmative vote of a majority of the shares represented at a shareholder meeting and entitled to vote for shareholder action, including the election of directors. Under the New Mexico Business Corporation Act, some corporate actions, including amending the articles of incorporation and approving a plan of merger, consolidation or share exchange, require the affirmative vote of a majority of the outstanding shares entitled to vote, which could include, in certain circumstances, classes of preferred stock.

Our articles of incorporation limit the Board to designating voting rights for series of preferred stock only (1) when we fail to pay dividends on the applicable series of preferred stock, (2) when proposed changes to the articles of incorporation would adversely impact preferred shareholders’ rights and privileges and (3) if the Board issues a new series of preferred stock convertible into common stock and confers upon the holders of such convertible preferred stock the right to vote as a single class with holders of common stock on all matters submitted to a vote of holders of common stock at a meeting of shareholders other than for election of directors, with the same number of votes as the number of shares of common stock into which the shares of such preferred stock are convertible, provided that at all times the aggregate preferred stock outstanding with such voting rights is convertible into no more than 12 million shares of common stock.

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Holders of each outstanding share of Series A Preferred Stock are entitled to vote as a single class with holders of our common stock on all matters submitted to our shareholders except the election of directors. Without first obtaining the consent or approval of the holders of a majority of the outstanding shares of Series A Preferred Stock, voting as a separate class, we cannot amend any provisions of our articles of incorporation in a manner that would have an adverse impact on the rights and privileges of the Series A Preferred Stock. Holders of our outstanding shares of Series A Preferred Stock are entitled to the number of votes corresponding to the number of shares of common stock into which such shares of Series A Preferred Stock are convertible on the record date for determining shareholders entitled to vote.

Our articles of incorporation do not allow our directors to create classes of directors. All directors are elected annually.

Liquidation Rights with Respect to Our Common Stock and Series A Preferred Stock

In the event we are liquidated or dissolved, either voluntarily or involuntarily, each share of Series A Preferred Stock is entitled to a liquidation preference of $1.00 per share. After that claim is satisfied, holders of our common stock are entitled to, ratably, an amount equal to (i) $1.00, divided by the number of shares of common stock into which a share of Series A Preferred Stock is then convertible, (ii) multiplied by the number of shares of common stock then outstanding. After that claim is satisfied, all remaining assets will be distributed to the holders of the Series A Preferred Stock and common stock ratably on the basis of the number of shares of outstanding common stock and, in the case of the Series A Preferred Stock, the number of shares of common stock into which the outstanding shares of Series A Preferred Stock are then convertible. The rights of the holders of our common stock to share ratably (according to the number of shares held by them) in the distribution of remaining assets will also be subject to the liquidation preferences and other rights of any additional series of preferred stock that we may issue in the future.

Preemptive Rights with Respect to Our Common Stock and Series A Preferred Stock

Neither the holders of our common stock nor the holders of our Series A Preferred Stock have a preemptive right to purchase shares of our authorized but unissued shares, or securities convertible into shares or carrying a right to subscribe to or acquire shares, except under the terms and conditions as may be provided by our Board in its sole judgment.

As discussed above, each share of Series A Preferred Stock is convertible at the option of the holder at any time into 10 shares of common stock, subject to certain anti-dilution adjustments.

Listing

Our common stock is listed on the New York Stock Exchange under the “TXNM” symbol.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A. 250 Royall Street, Canton, MA 02021.

Preferred Stock

Our Board is authorized, pursuant to our articles of incorporation, by resolution to provide for the issuance of up to 10,000,000 shares of preferred stock in one or more series and to fix, from time to time before issuance:

•the serial designation, authorized number of shares and the stated value;

•the dividend rate, if any, the date or dates on which the dividends will be payable, and the extent to which the dividends may be cumulative;

•the price or prices at which shares may be redeemed, and any terms, conditions and limitations upon any redemption;

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•the amount or amounts to be received by the holders in the event of our dissolution, liquidation, or winding up;

•any sinking fund provisions for redemption or purchase of shares of any series;

•the terms and conditions, if any, on which shares may be converted into, or exchanged for, shares of other capital stock, or of other series of preferred stock; and

•the voting rights, if any, for the shares of each series, limited to circumstances when (1) we fail to pay dividends on the applicable series of preferred stock, (2) proposed changes to the articles of incorporation would adversely impact preferred shareholders’ rights and privileges and (3) the Board issues a new series of preferred stock convertible into common stock and confers upon the holders of such convertible preferred stock the right to vote as a single class with holders of common stock on all matters submitted to a vote of holders of common stock at a meeting of shareholders other than for election of directors, with the same number of votes as the number of shares of common stock into which the shares of such preferred stock are convertible, provided that at all times the aggregate preferred stock outstanding with such voting rights is convertible into no more than 12 million shares of common stock. Currently, of the 10,000,000 authorized shares of preferred stock, 500,000 have been designated as Series A Preferred Stock, and no Series A Preferred Stock shares have been issued and are outstanding.

Prior to the issuance of shares of each series of our preferred stock, our Board is required to adopt resolutions and file articles of amendment with the New Mexico Public Regulation Commission. The certificate of amendment will fix for each series the designation and number of shares and the rights, preferences, privileges and restrictions of the shares subject to the limitations set forth above.

All shares of preferred stock will, when issued, be fully paid and nonassessable and will not have any preemptive or similar rights. We are not required by the New Mexico Business Corporation Act to seek shareholder approval prior to any issuance of authorized but unissued stock.

Limitation of Liability and Indemnification of Officers and Directors

Our articles of incorporation provide that liability for our directors for monetary damages will be eliminated or limited to the fullest extent permissible under New Mexico law, and our by-laws provide that we must indemnify our officers and directors to the fullest extent permissible under New Mexico law.

Certain Other Matters

Our articles of incorporation and by-laws include a number of provisions that may have the effect of discouraging persons from acquiring large blocks of our stock or delaying or preventing a change in our control. The material provisions that may have such an effect include:

•authorization for our Board to issue our preferred stock in series and to fix rights and preferences of the series (including, among other things, whether, and to what extent, the shares of any series will have voting rights, within the limitations described above, and the extent of the preferences of the shares of any series with respect to dividends and other matters);

•advance notice procedures with respect to any proposal other than those adopted or recommended by our Board; and

•provisions specifying that only a majority of the Board, the chairman of the Board, the president or holders of not less than one-tenth of all our shares entitled to vote may call a special meeting of stockholders.

Under the New Mexico Public Utility Act, approval of the New Mexico Public Regulation Commission is required for certain transactions which may result in our change in control or exercise of control.

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DESCRIPTION OF WARRANTS

This section describes the general terms of the warrants that we may offer and sell by this prospectus. This prospectus and any applicable prospectus supplement will contain the material terms and conditions for each warrant. The applicable prospectus supplement may add, update or change the terms and conditions of the warrants as described in this prospectus.

General

We may issue warrants to purchase debt securities, common stock or preferred stock. Warrants may be issued independently or together with any securities and may be attached to or separate from those securities. The warrants will be issued under warrant agreements to be entered into between us and a bank or trust company, as warrant agent, all of which will be described in the prospectus supplement relating to the warrants we are offering. The warrant agent will act solely as our agent in connection with the warrants and will not have any obligation or relationship of agency or trust for or with any holders or beneficial owners of warrants. A copy of the warrant agreement will be filed with the SEC in connection with the offering of the warrants.

Debt Warrants

We may issue warrants for the purchase of our debt securities. As explained below, each debt warrant will entitle its holder to purchase debt securities at an exercise price set forth in, or to be determinable as set forth in, the related prospectus supplement. Debt warrants may be issued separately or together with debt securities.

Any debt warrants will be issued under debt warrant agreements to be entered into between us and one or more banks or trust companies, as debt warrant agent, as will be set forth in the prospectus supplement relating to the debt warrants being offered by the prospectus supplement and this prospectus. A copy of the debt warrant agreement, including a form of debt warrant certificate representing the debt warrants, will be filed with the SEC in connection with the offering of the debt warrants.

The particular terms of each issue of debt warrants, the debt warrant agreement relating to the debt warrants and the debt warrant certificates representing debt warrants will be described in the applicable prospectus supplement, including, as applicable:

•the title of the debt warrants;

•the initial offering price;

•the title, aggregate principal amount and terms of the debt securities purchasable upon exercise of the debt warrants;

•the currency or currency units in which the offering price, if any, and the exercise price are payable;

•the title and terms of any related debt securities with which the debt warrants are issued and the number of the debt warrants issued with each debt security;

•the date, if any, on and after which the debt warrants and the related debt securities will be separately transferable;

•the principal amount of debt securities purchasable upon exercise of each debt warrant and the price at which that principal amount of debt securities may be purchased upon exercise of each debt warrant;

•if applicable, the minimum or maximum number of warrants that may be exercised at any one time;

•the date on which the right to exercise the debt warrants will commence and the date on which the right will expire;

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•if applicable, a discussion of United States federal income tax, accounting or other considerations applicable to the debt warrants;

•whether the debt warrants represented by the debt warrant certificates will be issued in registered or bearer form and, if registered, where they may be transferred and registered;

•anti-dilution provisions of the debt warrants, if any;

•redemption or call provisions, if any, applicable to the debt warrants; and

•any additional terms of the debt warrants, including terms, procedures and limitations relating to the exchange and exercise of the debt warrants.

Debt warrant certificates will be exchangeable for new debt warrant certificates of different denominations and, if in registered form, may be presented for registration of transfer and debt warrants may be exercised at the corporate trust office of the debt warrant agent or any other office indicated in the related prospectus supplement. Before the exercise of debt warrants, holders of debt warrants will not be entitled to payments of principal, premium, if any, or interest, if any, on the debt securities purchasable upon exercise of the debt warrants, or to enforce any of the covenants in the applicable indenture.

Equity Warrants

We may issue warrants for the purchase of our equity securities such as our preferred stock or common stock. As explained below, each equity warrant will entitle its holder to purchase equity securities at an exercise price set forth in, or to be determinable as set forth in, the related prospectus supplement. Equity warrants may be issued separately or together with equity securities.

Any equity warrants will be issued under equity warrant agreements to be entered into between us and one or more banks or trust companies, as equity warrant agent, as will be set forth in the prospectus supplement relating to the equity warrants being offered by the prospectus supplement and this prospectus. A copy of the equity warrant agreement, including a form of equity warrant certificate representing the equity warranty, will be filed with the SEC in connection with the offering of the equity warrants.

The particular terms of each issue of equity warrants, the equity warrant agreement relating to the equity warrants and the equity warrant certificates representing equity warrants will be described in the applicable prospectus supplement, including, as applicable:

•the title of the equity warrants;

•the initial offering price;

•the aggregate number of equity warrants and the aggregate number of shares of the equity security purchasable upon exercise of the equity warrants;

•the currency or currency units in which the offering price, if any, and the exercise price are payable;

•if applicable, the designation and terms of the equity securities with which the equity warrants are issued, and the number of equity warrants issued with each equity security;

•the date, if any, on and after which the equity warrants and the related equity security will be separately transferable;

•if applicable, the minimum or maximum number of the warrants that may be exercised at any one time;

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•the date on which the right to exercise the equity warrants will commence and the date on which the right will expire;

•if applicable, a discussion of United States federal income tax, accounting or other considerations applicable to the equity warrants;

•anti-dilution provisions of the equity warrants, if any;

•redemption or call provisions, if any, applicable to the equity warrants; and

•any additional terms of the equity warrants, including terms, procedures and limitations relating to the exchange and exercise of the equity warrants.

Holders of equity warrants will not be entitled, solely by virtue of being holders, to vote, to consent, to receive dividends, to receive notice as shareholders with respect to any meeting of shareholders for the election of directors or any other matter, or to exercise any rights whatsoever as a holder of the equity securities purchasable upon exercise of the equity warrants.

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DESCRIPTION OF SECURITIES PURCHASE CONTRACTS

This section describes the general terms of the securities purchase contracts that we may offer and sell by this prospectus. This prospectus and any prospectus supplement will contain the material terms and conditions for each securities purchase contract. A prospectus supplement may add, update or change the terms and conditions of the securities purchase contracts as described in this prospectus.

We may issue securities purchase contracts, representing contracts obligating holders to purchase from or sell to us, and obligating us to sell to or purchase from the holders, a specified number of shares of common stock or preferred stock or a specified number of equity warrants, at a future date or dates, or a variable number of shares of common stock or preferred stock or a variable number of equity warrants for a stated amount of consideration. The price per share or per equity warrant and the number of shares of common stock or preferred stock or the number of equity warrants may be fixed at the time the securities purchase contracts are issued or may be determined by reference to a specific formula set forth in the securities purchase contracts. Any such formula may include anti-dilution provisions to adjust the number of shares of common stock or preferred stock or the number of equity warrants issuable pursuant to the securities purchase contracts upon certain events.

We also may issue securities purchase contracts, representing contracts obligating holders to purchase from or sell to us, and obligating us to sell to or purchase from the holders, a specified principal amount of debt securities or debt warrants at a future date or dates. The purchase price and the interest rate may be fixed at the time the securities purchase contracts are issued or may be determined by reference to a specific formula set forth in the securities purchase contracts.

The securities purchase contracts may require holders to secure their obligations in a specified manner and in certain circumstances we may deliver newly issued prepaid securities purchase contracts upon release to a holder of any collateral securing such holder’s obligations under the original securities purchase contract.

The applicable prospectus supplement will describe the general terms of any securities purchase contracts and, if applicable, prepaid securities purchase contracts. The description in the prospectus supplement will not purport to be complete and will be qualified in its entirety by reference to:

•the securities purchase contracts;

•the collateral arrangements and depositary arrangements, if applicable, relating to such securities purchase contracts; and

•if applicable, the prepaid securities purchase contracts and the document pursuant to which such prepaid securities purchase contracts will be issued.

Material United States federal income tax considerations applicable to the securities purchase contracts also will be discussed in the applicable prospectus supplement.

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DESCRIPTION OF UNITS

We may issue units comprising one or more of the other securities described in this prospectus in any combination. Units also may include debt obligations of third parties, such as U.S. Treasury securities. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately at any time or at any time before a specified date.

The applicable prospectus supplement may describe:

•the designation and terms of the units and of the securities composing the units, including whether and under what circumstances those securities may be held or transferred separately;

•any provisions for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units; and

•whether the units will be issued in fully registered or global form.

The applicable prospectus supplement will describe the terms of any units. The preceding description and any description of units in the applicable prospectus supplement does not purport to be complete and is subject to and is qualified in its entirety by reference to the unit agreement and, if applicable, collateral arrangements and depositary arrangements relating to such units, which documents will be filed with the SEC in connection with the offering of any units.

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PLAN OF DISTRIBUTION

We may sell the securities, in or outside of the United States, to underwriters or dealers, through agents, directly to purchasers or through a combination of these methods. The applicable prospectus supplement will contain specific information relating to the terms of the offering, including, to the extent not otherwise included in the prospectus:

•the name or names of any underwriters or agents;

•the purchase price of the securities;

•our net proceeds from the sale of the securities;

•any underwriting discounts or agency fees and other items constituting underwriters’ or agents’ compensation;

•any initial public offering price and any discounts or concessions allowed or re-allowed or paid to dealers; and

•any securities exchange on which the securities may be listed.

By Underwriters

If underwriters are used in the sale, the securities will be acquired by the underwriters for their own account. Underwriters may offer the securities directly or through underwriting syndicates represented by one or more managing underwriters. The underwriters may resell the securities in one or more transactions, including negotiated transactions, at a fixed public offering price, which may be changed, at market prices prevailing at the time of the sale, at prices based on prevailing market prices or at negotiated prices. Unless otherwise set forth in the applicable prospectus supplement, the obligations of the underwriters to purchase the securities will be subject to certain conditions.

By Dealers

If dealers are used in the sale, unless otherwise specified in the applicable prospectus supplement, we will sell the securities to the dealers as principals. The dealers may then resell the securities to the public at varying prices to be determined by the dealers at the time of resale. The applicable prospectus supplement will contain more information about the dealers, including the names of the dealers and the terms of our agreement with them.

By Agents and Direct Sales

We may sell the securities directly to the public, without the use of underwriters, dealers or agents. We may also sell the securities through agents we designate from time to time. The applicable prospectus supplement will contain more information about the agents, including the names of the agents and any commission we agree to pay the agents.

We also may engage a broker-dealer from time to time to act as agent or principal for the offer of the securities in one or more placements pursuant to a distribution agreement. If we and the broker-dealer agree, we will sell to the broker-dealer as agent or as principal, and the broker-dealer will seek to solicit offers to purchase on an agency basis and/or will purchase on a principal basis, the securities. The number and purchase price (less an underwriting discount) of the securities we sell to the broker-dealer will be mutually agreed on the relevant trading day. The securities sold under the distribution agreement will be sold at prices related to the prevailing market price for such securities, and therefore exact figures regarding the price, proceeds that will be raised or commissions to be paid will be described in a prospectus supplement to this prospectus or in other filings made in accordance with and as permitted by the Securities Act and the Exchange Act. The broker-dealer may make sales of the securities pursuant to the distribution

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agreement in privately negotiated transactions and/or any other method permitted by law deemed to be an “at-the-market” offering as defined in Rule 415 promulgated under the Securities Act including sales made on the New York Stock Exchange, the current trading market for our common stock.

General Information

Underwriters, dealers and agents that participate in the distribution of the securities may be deemed underwriters as defined in the Securities Act, and any discounts or commissions we pay to them and any profit made by them on the resale of the securities may be treated as underwriting discounts and commissions under the Securities Act. Any underwriters, dealers or agents will be identified and their compensation from us will be described in the applicable prospectus supplement. Any initial public offering price and any discounts or concessions allowed or reallowed or paid to dealers may be changed from time to time.

We may agree with the underwriters, dealers and agents to indemnify them against certain civil liabilities, including liabilities under the Securities Act, or to contribute with respect to payments which the underwriters, dealers or agents may be required to make.

Underwriters, dealers and agents may be customers of, engage in transactions with or perform services for, us in the ordinary course of their businesses. We will describe in the applicable prospectus supplement naming the underwriters, dealers or agents, the nature of any material relationship between us and the underwriters, dealers or agents, respectively. 

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LEGAL MATTERS

Certain legal matters in connection with the securities offered hereby will be passed upon for us by Leonard D. Sanchez, Esq., Associate General Counsel of TXNM, and, unless otherwise indicated in the applicable prospectus supplement, certain other matters will be passed upon for us by Troutman Pepper Locke LLP. If legal matters in connection with offerings made pursuant to this prospectus are passed upon by counsel for the underwriters, dealers or agents, if any, such counsel will be named in the applicable prospectus supplement relating to such offering. As of December 31, 2024, Mr. Sanchez held 2,441 shares of TXNM common stock (pursuant to the vesting of restricted stock rights) and 1,499 restricted stock rights (which vest in equal annual installments over a three-year period from the respective grant date).

EXPERTS

The consolidated financial statements and schedules of TXNM Energy, Inc. as of December 31, 2024 and 2023, and for each of the years in the three-year period ended December 31, 2024, and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2024 have been incorporated by reference herein in reliance upon the report of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

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TXNM Energy, Inc.

$400,000,000 of Shares of Common Stock

PROSPECTUS SUPPLEMENT

August , 2026

Wells Fargo Securities