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Kelly Criterion
Kelly Criterion Calculator
Find the optimal bet size to maximize long-term bankroll growth based on your edge and odds.
American: -110, +150 | Decimal: 1.91 | Fractional: 10/11
Your honest estimate — not the implied probability from the line.
Kelly Fraction
Most bettors use half or quarter Kelly to reduce variance.
Recommended Stake
$0.00
0.00% of bankroll
Full Kelly
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Your Edge
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Implied Probability
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Expected Value
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How the Kelly formula works
The Kelly Criterion determines the optimal fraction of your bankroll to wager:
f* = (b × p − q) ÷ b
- f* — fraction of bankroll to bet
- b — decimal odds minus 1 (net profit per $1 staked)
- p — your estimated win probability
- q — loss probability (1 − p)
If f* is zero or negative, there is no positive edge — the calculator recommends no bet.
Prediction market prices: enter the contract price in cents (e.g. 52¢). A 52¢ price means you pay $0.52 to win $1 — equivalent to 52% implied probability.