The Kelly Criterion estimates the mathematically optimal fraction of your account to risk per trade, given your historical win rate and win/loss ratio. Most traders use a fraction of full Kelly (half or quarter) to reduce variance.
Average win/loss can be in £, $, pips, or R-multiples — only the ratio between them matters, so use whatever unit your trade history is recorded in.
Half Kelly (Recommended)
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The percentage in each box is the share of your total account balance (the figure entered above, not your last trade or profit target) to risk on this single trade. The amount underneath it is that percentage converted into your account currency — e.g. Half Kelly at 5.0% on a £10,000 account risks £500 on the trade.
Enter the current price alongside a target price for a currency pair to see the distance between them in price terms, pips, and percentage, then add a lot size to see what that move is worth.
Lot size is in standard lots (100,000 units for forex, or this pair's typical commodity contract size for metals/oil) — used to value the move to your target price below.
Value of move (quote currency, at entered lot size)
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Combine your Kelly-suggested risk amount with a stop-loss distance (in pips) to get the exact lot size to trade. Pip value is taken automatically from the Calculator box above (based on the pair selected there).
Suggested position size
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Risk Amount auto-fills from the Half Kelly amount above — override it to test a different scenario. Pick whichever currency your account is denominated in; "Other" lets you type a custom symbol or code (e.g. Fr, A$, kr).