Free tool
Position size calculator
How much to risk on this trade, to the cent.
Amount at risk
$100
Position size
10,000
Notional
$11,000
You lose exactly $100 if price hits your stop — whatever the distance.
Position size is the first pillar of risk management: it determines how many units (lots, contracts, shares) to buy so you only risk a fixed amount if your stop is hit. The formula is simple: risk amount = account × risk%, then size = risk amount ÷ distance to stop. The result: whatever the volatility, each loss stays identical and controlled. That's what separates a disciplined trader from an account that blows up on a single bad trade.
Go from calculation to proof
These numbers are estimates. On GetBacktest, backtest your strategy tick by tick on real data and get a true robustness verdict.
Backtest for freeFrequently asked questions
How do I calculate my position size?
Divide the amount you're willing to lose (account × risk%) by the distance between your entry and your stop. You get the number of units to trade.
What risk per trade should I choose?
Most disciplined traders risk 0.5 to 2% per trade. The lower the risk, the more the risk of ruin drops — test it with the risk-of-ruin calculator.
Does position sizing guarantee profit?
No, but it guarantees survival. Without a positive expectancy, no sizing makes you profitable; without sizing, a positive expectancy can still ruin an account.
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