The Kelly criterion is a formula that sizes bets to maximize long-run wealth growth. Enter your estimated win probability and payoff odds, and this free tool computes the optimal fraction of bankroll to stake — plus half and quarter Kelly for the cautious.
Your edge
No edge — the math says don't bet. The Kelly fraction is zero or negative. The curve below shows why.
Optimal stake
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Full Kelly
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Half Kelly
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Quarter Kelly
Expected growth vs stake fraction
expected log-growthruin zone (f ≥ 1)Kelly optimum
Why log growth? Kelly maximizes the geometric growth rate — the only objective that survives thousands of bets without gambler's ruin.
Why fractional Kelly? Full Kelly assumes your probability estimate is perfect. It isn't. Half Kelly keeps ~75% of the growth with half the volatility.
Garbage in: overestimate your win rate by 5 points and the "optimal" stake can double. Round your edge down.