LEARN
Forex Position Sizing Calculator: A Step‑by‑Step Guide 2026
Learn how to use a forex position sizing calculator to manage risk, size trades, and boost performance with step‑by‑step guide, video demo, and tool comparison.
Kelly criterion calculator
The share of the account the Kelly formula would put at risk on each trade, from a win rate and payoff, with the more cautious half and quarter.
Result
Full Kelly
8.33%
Of equity at risk per trade, the share that maximises long-run growth if the inputs are exactly right.
- Payoff ratio
- 1.50 : 1
- Half Kelly
- 4.17%
- Quarter Kelly
- 2.08%
Kelly assumes the win rate and averages are known exactly and every trade is independent. Real figures come from a sample and shift over time, so full Kelly usually risks too much: many traders use a half or a quarter of it, and many use less.
This tool uses no exchange rates. Everything is calculated in your browser; nothing you enter is sent anywhere.
How it is calculated
The Kelly criterion finds the fixed fraction of capital that would grow an account fastest over many bets, if the odds were known exactly.
b = average win ÷ average lossKelly fraction = (b × p − q) ÷ bp = win rate, q = 1 − p
In trading the odds are estimated, not known, and an estimate that is too high leads to sizes that are far too large. Full Kelly also brings deep drawdowns even when the estimate is right. That is why traders who use it at all usually take a half or a quarter.
Worked example
- Win rate 45%, average win 150, average loss 100: b = 1.5.
- (1.5 × 0.45 − 0.55) ÷ 1.5 = (0.675 − 0.55) ÷ 1.5 = 8.33% of equity.
- Half Kelly is 4.17%, quarter Kelly 2.08%.
Risk. These tools do arithmetic on the figures you enter. They are not advice, and unless a field asks for them they leave out spreads, commission, financing and slippage. Past results do not predict future ones. Trading leveraged currency products carries a high risk of loss. Read our financial disclaimer.