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Kelly criterion calculator

The Kelly criterion sizes a bet by the edge you think you have: bigger edges, bigger bets, and no bet at all without one.

Bet this much of your bankroll
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Stake
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EV
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per dollar staked

How it works

The formula

Kelly stake = (win probability × decimal odds − 1) ÷ (decimal odds − 1), as a share of your bankroll. At +120 (2.20) with a 50% chance: (0.50 × 2.20 − 1) ÷ 1.20 = 8.33% for full Kelly, 4.17% for half.

Why a fraction

Full Kelly grows a bankroll fastest in theory, but only if your probabilities are right; even then, the chance of your bankroll halving at some point along the way is about 50%. Overestimating your edge makes Kelly overbet, so most bettors use half or a quarter.

No edge, no bet

If your win probability is at or below the break-even rate for the odds, Kelly says to bet nothing. The EV calculator shows the break-even rate for any price.

Several bets at once

This sizes one bet at a time. When bets run at the same time, sizing each with the full formula adds up to too much; scale down, or keep to a small fraction.

More calculators

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Parlay calculatorOdds and payout for a parlay of up to 15 legs, with pushes. Round robin calculatorEvery parlay in a round robin: how many bets, the risk and the payout. Bet payout calculatorWhat a bet pays at American odds, or what to risk to win a set amount. Odds converterAmerican, decimal and fractional odds and implied probability. No-vig fair odds calculatorTake the vig out of a market: fair odds, fair win % and the hold. Hedge calculatorHow much to bet on the other side to lock in a profit or get your stake back. Expected value calculatorA bet's expected profit from the odds and your win probability. Arbitrage calculatorStakes across two or three prices that pay the same whatever happens. Closing line value calculatorHow the odds you took compare with the closing line. Prediction market calculatorAny prediction market price as odds after its fee, next to a sportsbook's.

For information only: check every figure with your sportsbook or exchange before you bet. Calculators can't make a bet a good one, and only bet what you can afford to lose.