Position size calculator
Work out how many lots to trade from your account size, the risk you are willing to take, and the distance to your stop. Nothing is hard-coded — you supply your broker's contract specification.
Inputs
Where do those two numbers come from?Open your broker's contract specification for the instrument. Contract size is how many units one lot represents, and value of 1 lot per 1.0 price move is what one lot gains or loses when the price moves one whole unit, in your account currency. They differ by instrument and by broker — for the same symbol, one broker may use a contract size ten times another. That is precisely why this page does not guess them for you.
Result
- Price distance to stop
- 20.0000
- Cash at risk if the stop is hit
- 100.00
- Notional value of the position
- 12,000.00
The formula, so you can check it
cash at risk = balance x risk% risk per unit = |entry - stop| risk per lot = risk per unit x value of 1 lot per 1.0 move lots = cash at risk / risk per lot units = lots x contract size notional = units x entry price
Note that position size does not depend on your leverage setting. Leverage decides how much margin the broker holds, not how much you lose when the price moves — a one-lot position loses the same amount whether it is held at 1:1 or 1:500. Sizing by risk and sizing by margin are two different calculations, and only the first one protects the account.
A worked example, so you can sanity-check the tool
Take a 10,000 account, risking 1% per trade — 100 in cash. You want to buy at 2,400 with a stop at 2,380, so the stop is 20.00 away. Using one common gold specification (contract size 100 units per lot, one lot worth 100 per 1.0 of price movement):
cash at risk = 10,000 x 1% = 100.00 risk per unit = |2,400 - 2,380| = 20.00 risk per lot = 20.00 x 100 = 2,000.00 lots = 100 / 2,000 = 0.05 units = 0.05 x 100 = 5 units notional = 5 x 2,400 = 12,000.00
Note the notional: a 12,000 position on a 10,000 account, sized so that a 20-point move costs 1%. That is normal and it is why position size and leverage are different subjects. Now shrink the account to 500 with everything else unchanged: the arithmetic asks for 0.0025 lots, which is below any broker's minimum step. The smallest position you can actually take is 0.01 lots, which risks 20.00 — 4% of that account, four times what you intended. Nothing about the strategy changed; the account size did.
What this calculator does not include
- Spread and commission. They are charged on every trade, so your realised loss on a stopped-out trade is larger than the planned risk shown above.
- Slippage and gaps. A stop is an instruction, not a guarantee. Weekend gaps and fast markets can fill well past your level, and no sizing rule can account for an event that has not happened yet.
- Currency conversion.If your account currency differs from the instrument's quote currency, your broker applies a conversion rate that changes the risk per lot. Enter the value of 1 lot per 1.0 price move in your account currency to include it.
- Swap and financing. Relevant for positions held overnight, and not part of the entry risk.
- Correlated positions. If you size five trades this way and they are all bets on the same move, your real risk is not 1% — it is closer to 5%. Position size per trade is not portfolio risk.
Related reading
- Position sizing on gold (XAUUSD): turning lot size into real risk
- Minimum account size for trading, and why your rule may not fit
- The Kelly criterion formula, and why full Kelly usually fails
- Risk of ruin formula: how to calculate it
- Why a 70% win rate can still lose money
This tool is arithmetic, not advice. It does not know whether your stop is in a sensible place — only you can decide that, and a correct position size on a bad stop is still a bad trade.