Position Size Calculator

How many shares should you buy? This free position size calculator works backward from the amount you are willing to lose. Enter your account size, the percentage of the account you want to risk on one trade, your entry price, and your stop-loss price. The calculator shows how many units to trade so that, if your stop is hit, the loss stays within your limit.

Position Size Calculator

Any currency
Many traders use 0.5%–2%
Below entry = long, above entry = short
Position size (units)
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Position value
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Maximum risk
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Risk per unit
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% of account
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Reward : risk
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Units are rounded down to whole shares. The calculation does not include commissions, spreads, or slippage – and a stop-loss may be filled at a worse price if the market gaps. For fractional instruments, adjust accordingly.

How Position Sizing Works

The calculation has three steps:

  1. Maximum risk = account size × risk %. For example, 1% of $100,000 is $1,000.
  2. Risk per unit = the distance between your entry and your stop. Entry $50 and stop $45 means $5 of risk per share.
  3. Position size = maximum risk ÷ risk per unit. $1,000 ÷ $5 = 200 shares, a position worth $10,000.

Notice that the stop distance, not the price of the stock, determines the size. A wider stop means a smaller position; a tighter stop allows a larger one.

Why It Matters

Consistent position sizing keeps any single trade from doing serious damage. If each trade risks only 1% of the account, even a string of ten losses in a row costs roughly 10% – painful, but recoverable. Without a sizing rule, one or two bad trades can wipe out months of progress. Read more in our guide to risk management.

Limitations to Keep in Mind

  • Gaps and slippage: a stop-loss order can be filled below your stop price in a fast market or after overnight news. See stop-loss vs. stop-limit orders.
  • Costs: commissions, spreads, and currency conversion add to the real loss.
  • Correlation: several positions in similar stocks can all be stopped out together, so total risk may be larger than it looks.
  • Discipline: the calculator only helps if you respect the stop. Moving it further away or adding to a losing position defeats the purpose – see how to handle trading losses.

Learn More

This calculator is for general educational purposes only. Results are estimates based on the numbers you enter and simplified assumptions; they are not financial, investment, or tax advice. See our Disclaimer.

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