Position Size Calculator
Work out how many shares to buy so a stop-loss limits your loss to a set percentage of your account — plus the risk/reward ratio to your target.
For information and education only — not financial advice. Results are estimates based on the numbers you enter; check important decisions with a qualified professional.
How to use
- 1Enter your account size and the percentage you're willing to risk on the trade.
- 2Enter the entry, stop-loss and (optionally) target prices.
How it's calculated
Shares = (account × risk %) ÷ (entry − stop). Risk/reward = (target − entry) ÷ (entry − stop). Break-even win rate = 1 ÷ (1 + R).
Frequently asked questions
How much should I risk per trade?
Many traders risk 1–2% of their account per trade, so a losing streak doesn't wipe them out.
What's a good risk/reward ratio?
Often 1:2 or better — then you can be profitable even if you win only about a third of your trades.
Does this account for slippage?
No. Stops can fill below your price in fast markets or gaps, so actual losses can exceed the plan.