Kelly Criterion Calculator
Using Kelly Without Overbetting
Kelly is the fraction of capital that maximises the geometric growth rate when you know your edge. It falls straight out of win rate and payoff: with a 55% win rate on even-money bets the answer is 10%, and any higher stake reduces long-run growth even though it raises expected value per trade.
Full Kelly is famously volatile. Estimates of win rate and payoff are wrong precisely when it matters, so practitioners run quarter or half Kelly, trading a little growth for a much shallower drawdown path.
Negative Kelly is meaningful: it means the edge does not justify the stake, and the growth-maximising position is to not take the trade at all.
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How it is calculated
f* = (bp − q) / bp = wins / trialsq = 1 − pMost practitioners use fractional Kelly (¼–½) to cut volatility.
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Reading the number
Enter values to see a practical interpretation.
The tool turns your edge and offered odds into the classic fraction, then suggests the conservative half-Kelly stake.
Estimated win rates drift, bookmaker limits shrink stakes, and overbetting a real edge still ends in a drawdown.
Reference example: p = 0.55, b = 1 → f* = 10% of capital; half-Kelly = 5%.
Reviewed August 21, 2026.
Primary references: Kelly 1956 paper · Thorp 2006 — Kelly
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