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Kelly Criterion Calculator
Optimal bet sizing based on your edge — not your gut.
Recommended stake
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% of bankroll
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Your edge
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The Kelly formula, explained
The numerator (p × o − 1) is your edge: the gap between your estimated probability and the one implied by the odds. Example: you estimate a 52% win probability at 2.10 odds. Edge = 0.52 × 2.10 − 1 = +9.2%. Full Kelly = 0.092 ÷ 1.10 ≈ 8.4% of bankroll — and a more sensible half-Kelly ≈ 4.2%.
Three properties worth remembering:
- No edge, no bet. If your probability doesn't beat the odds, the formula goes negative: don't bet.
- The stake scales with your edge — not with subjective confidence or the urge to chase losses.
- Full Kelly is brutal: a few points of estimation error cost dearly. Hence half-Kelly as the default.
After the calculation?
Kelly is useless without tracking: you need your real hit rate to estimate p. MyBankroll computes your ROI, CLV and Kelly staking from your actual bets.
Try MyBankroll free for 7 daysFAQ
What is the Kelly Criterion formula?
Stake = Bankroll × (p × o − 1) ÷ (o − 1), where p is your estimated win probability and o the decimal odds. The result is the fraction of your bankroll to stake. If (p × o − 1) is negative, you have no edge and the recommended stake is zero.
Why bet half-Kelly or quarter-Kelly?
Full Kelly maximizes theoretical growth but assumes your probability estimate is exact — it never is. Betting half or a quarter of the Kelly stake sharply reduces variance and protects your bankroll against estimation errors. Most serious bettors use fractional Kelly.
What if the calculator says “no bet”?
It means the odds are lower than your estimated probability implies: the bet has no value. Betting anyway means accepting negative expected value. That is half the point of the Kelly Criterion — it also tells you when NOT to bet.
Go further
Informational tool. The Kelly Criterion guarantees nothing: it optimizes stake size only if your probability estimate is reliable. Gambling involves risk. Please bet responsibly. 18+/21+.