Calculator
Position Size Calculator
What it calculates
Disciplined investors decide how much to lose before they decide how much to make. This calculator sizes a position from your account value, the percentage you're willing to risk, and the distance to your stop-loss — so a single idea can't sink your portfolio.
How this position size calculator works
The calculator starts with the maximum dollar loss you accept, then divides it by the distance between your entry and stop price to determine the largest whole-share position within that risk budget.
Formula
Shares = floor((Account value × risk %) ÷ |Entry price − stop price|)
Stops can gap or fill worse than expected. Position size is a risk-control input, not a prediction of a trade's outcome.
Primary specifications
Before you use the result
Assumptions
- • The stop order fills at the price entered.
- • The calculation uses whole shares and excludes commissions, spreads, taxes, and slippage.
- • The risk percentage is based on total account value, not a guarantee of maximum loss.
Quick start
- 1. Choose the account value and the maximum percentage you are prepared to lose.
- 2. Set an entry price and a stop based on your trade plan.
- 3. Use the resulting share count as a ceiling, then reduce it if liquidity or event risk warrants.
Inputs and units
| Input | Unit | Default |
|---|---|---|
| Account value | US dollars | $50,000 |
| Risk per trade | percent of account value | 1% |
| Entry price | US dollars per share | $100 |
| Stop-loss price | US dollars per share | $92 |
Worked example (hypothetical)
Position Size Calculator: worked example
Hypothetical example using the calculator's default inputs. The numbers are illustrative, not a forecast.
| Account value | $50,000 |
|---|---|
| Risk per trade | 1% |
| Entry price | $100 |
| Stop-loss price | $92 |
| Amount at risk | $500 |
|---|---|
| Shares | 62 |
| Position size | $6,200 |
$500 of risk divided by $8 of risk per share allows 62 shares, a $6,200 position.
How to interpret the result
Treat the share count as a ceiling. A stop can gap and fill below the price entered, so reduce the size ahead of earnings or in thinly traded stocks.
Frequently asked questions
How much of my account should I risk per position?
Many risk-managed investors cap the loss on any single position at 1–2% of total account value. This keeps a string of losing trades survivable.
What is a stop-loss?
A stop-loss is a predetermined price at which you'll exit to cap your loss. The distance between your entry and stop, combined with your risk budget, determines how many shares you can buy.
Can a stop order fill below the stop price?
Yes. Once triggered, a stop order generally becomes a market order and can execute at a worse price during gaps or fast markets.
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