NB Bancorp director reports tax-withheld shares

NB Bancorp, Inc. director Mark Whalen reported routine share movements related to compensation and holdings.

Rhea-AI Filing Summary

NB Bancorp, Inc. director Mark Whalen reported routine share movements related to compensation and holdings. The Form 4 shows a tax-withholding disposition of 4,918 shares of common stock at $19.82 per share, used to satisfy tax obligations rather than an open-market sale. After this transaction, Whalen directly owns 72,721 common shares. He also indirectly holds 30,000 shares as trustee for a trust. Footnotes indicate his position includes restricted stock that vests 20% per year starting on April 24, 2026, and another grant that vests 100% on January 2, 2027, reflecting ongoing equity-based compensation.

Insider Trade Summary

Exercise Price or Tax Liability: 4,918 shares

Exercise Price or Tax Liability 2 txns

Insider Whalen Mark

Role Director

Type	Security	Shares	Price	Value
Exercise Price or Tax Liability	Common Stock	4,918	$19.82	$97K
holding	Common Stock	--	--	--

Holdings After Transaction: Common Stock — 72,721 shares (Direct); Common Stock — 30,000 shares (Indirect, As trustee for trust)

Footnotes (2)

1. F1. Includes shares of restricted stock which vest at a rate of 20% per year commencing on April 24, 2026.
2. F2. Includes shares of restricted stock which vest 100% on January 2, 2027.

Key Figures

Tax-withheld shares: 4,918 shares Tax-withholding price: $19.82 per share Direct holdings after transaction: 72,721 shares +3 more

6 metrics

Tax-withheld shares 4,918 shares Common Stock disposed of for tax withholding at $19.82 per share

Tax-withholding price $19.82 per share Value used for the 4,918-share tax-withholding disposition

Direct holdings after transaction 72,721 shares Common Stock directly owned by Mark Whalen following the Form 4 transactions

Indirect trust holdings 30,000 shares Common Stock held indirectly as trustee for a trust

Restricted stock vesting start April 24, 2026 Restricted stock vests 20% per year commencing on this date

Single-date vesting January 2, 2027 Restricted stock grant vests 100% on this date

Key Terms

tax-withholding disposition, restricted stock, vest 100%, as trustee for trust, +1 more

5 terms

tax-withholding disposition financial

"transaction_action": "tax-withholding disposition""

A tax-withholding disposition is an event or transaction—such as selling or transferring securities, exercising options, or receiving compensation—that triggers a requirement to hold back part of the payment and remit it to tax authorities. It matters to investors because it reduces the cash they receive immediately and can change the timing and amount of taxable income, like a cashier taking a portion of your sale proceeds to pay taxes before you get the rest.

restricted stock financial

"Includes shares of restricted stock which vest at a rate of 20% per year"

Shares granted to an individual that carry limits on transfer or sale until certain conditions are met, such as staying with the company for a set time or hitting performance targets. Think of them as a locked gift that gradually opens; for investors they matter because they affect how many shares may enter the market later, signal management incentives and potential dilution, and reveal confidence in future company performance.

vest 100% financial

"Includes shares of restricted stock which vest 100% on January 2, 2027."

as trustee for trust financial

"direct_or_indirect": "I", "nature_of_ownership": "As trustee for trust""

Common Stock financial

"security_title": "Common Stock""

Common stock represents ownership shares in a company, giving investors a stake in its success and a say in important decisions through voting rights. It is the most common type of stock traded on markets and can provide income through dividends, as well as potential for value growth. For investors, holding common stock means sharing in the company’s profits and risks.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What insider transaction did NB Bancorp (NBBK) report for Mark Whalen?

NB Bancorp reported that director Mark Whalen had 4,918 common shares disposed of as a tax-withholding transaction. The shares were valued at $19.82 each and were used to cover tax obligations tied to equity compensation, not an open-market sale.

How many NB Bancorp (NBBK) shares were involved in the tax-withholding event?

The filing shows 4,918 shares of NB Bancorp common stock were withheld in a tax-withholding disposition. These shares were valued at $19.82 per share and were delivered to satisfy exercise price or tax liabilities associated with Whalen’s equity compensation.

How many NB Bancorp (NBBK) shares does Mark Whalen hold after this Form 4?

After the reported transactions, Mark Whalen directly owns 72,721 NB Bancorp common shares. He also indirectly holds 30,000 additional shares as trustee for a trust, giving him substantial ongoing exposure to the company’s stock through both direct and indirect ownership.

Is the NB Bancorp (NBBK) Form 4 transaction an open-market sale?

No, the Form 4 describes a tax-withholding disposition, not an open-market sale. The 4,918 shares were delivered to cover tax obligations or exercise price, a common administrative step when restricted stock or similar awards vest, rather than a discretionary sale into the market.

What restricted stock vesting schedule does Mark Whalen have at NB Bancorp (NBBK)?

Footnotes state that some of Whalen’s restricted stock vests 20% per year beginning April 24, 2026. Another restricted stock award vests 100% on January 2, 2027, indicating a multi-year equity compensation structure that gradually delivers full ownership over time.

How are Whalen’s indirect NB Bancorp (NBBK) shareholdings structured?

The filing reports 30,000 NB Bancorp common shares held indirectly by Mark Whalen as trustee for a trust. This indicates the shares are legally owned through a trust structure, with Whalen acting in a trustee capacity rather than holding them solely in his personal name.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 04/27/2026 - 02:50 PM EDT Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Whalen Mark

(Last) (First) (Middle)

1063 GREAT PLAIN AVE

(Street)

NEEDHAM MASSACHUSETTS 02492

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
NB Bancorp, Inc. [ NBBK ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
04/24/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	04/24/2026		F		4,918	D	$19.82	72,721(1)(2)	D
Common Stock								30,000	I	As trustee for trust

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. Includes shares of restricted stock which vest at a rate of 20% per year commencing on April 24, 2026.

2. Includes shares of restricted stock which vest 100% on January 2, 2027.

	/s/ Steven Lanter, pursuant to power of attorney	04/27/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)