Position Size Calculator
Size a trade to a fixed percentage of your account: how many shares to buy so your stop-loss risks only what you decide.
How it works
Risk amount = account × risk% · Shares = risk amount ÷ |entry − stop| · Position value = shares × entry
Good risk management fixes how much you can lose per trade, then works backwards to the position size — not the other way around. You decide the account percentage you are willing to risk, divide that dollar amount by the distance from your entry to your stop-loss, and the result is the number of shares that makes a stop-out cost exactly that much. A wider stop forces a smaller position, and a tighter stop allows a larger one, keeping your dollar risk constant.
Worked example
On a $10,000 account risking 1% ($100), with a $50 entry and a $48 stop, the risk per share is $2. Shares = 100 ÷ 2 = 50, a $2,500 position. If the stop triggers you lose 50 × $2 = $100 — exactly the 1% you chose.
Frequently asked questions
Why size to risk instead of a fixed dollar amount?
Fixing the risk keeps every losing trade about the same size, so a string of losses cannot blow up your account. It automatically buys fewer shares when your stop is far away and more when it is close.
What risk percentage should I use?
Many traders cap risk at 1–2% of the account per trade. Lower percentages survive long losing streaks more comfortably; higher ones grow faster but risk deep drawdowns. The right number depends on your strategy and tolerance.
Does this include leverage or fees?
No — it sizes the share count from your stop distance alone. If the position value exceeds your cash you would need margin, and commissions and slippage add a little to the real loss at the stop.
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Educational estimate, not investment advice. Markets involve risk of loss.