Stock Position Size Calculator
Calculate the optimal number of shares to buy based on your account size, risk tolerance, and stop-loss level. Position sizing is the foundation of risk management — it ensures no single trade can blow up your account.
With a $25,000 account risking 2% per trade, you have $500 of risk budget. If you enter a stock at $50 with a stop-loss at $47 (risk of $3/share), you should buy 166 shares ($8,300 position). If the stop hits, you lose exactly $498 — just under your 2% limit.
Enter Trade Parameters
Size your position based on riskResults
Your calculated position sizeEnter your trade parameters and click calculate to see your optimal position size.
Frequently Asked Questions
Key concepts for managing trade risk
Why is position sizing important?
Position sizing is the foundation of risk management and arguably the most important concept in trading. Even the best strategy with an 80% win rate will eventually blow up your account if you risk too much per trade. The goal is to survive losing streaks — which will happen to every trader — so you can benefit from winning streaks.
Professional traders typically risk 1-2% of their account per trade. At 2% risk, you could lose 10 trades in a row and still have over 80% of your account intact. At 10% risk per trade, those same 10 losses leave you with only 35% — a hole that's nearly impossible to dig out of. Position sizing keeps you in the game.
What is the risk-reward ratio and why does it matter?
The risk-reward ratio compares how much you stand to lose versus how much you stand to gain on a trade. A 2:1 ratio means your potential profit is twice your potential loss. This is powerful because it means you can be wrong 50% of the time and still come out profitable — every win covers two losses.
At a 3:1 ratio, you only need to win 25% of your trades to break even. At 1:1, you need to be right more than half the time just to stay flat. This is why experienced traders aim for at least a 2:1 risk-reward ratio on every trade. It gives you a mathematical edge even with a modest win rate, and it shifts the pressure from needing to be right all the time to simply managing your risk well.
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All calculations run entirely in your browser. We never collect, store, or transmit any data you enter into this calculator. There are no APIs, no server requests, and no logs — your financial information stays on your device and disappears when you close the page.