Find the mathematically optimal stake size for any bet. Maximize long-term bankroll growth without risking ruin.
The Kelly Criterion is a formula that determines the optimal fraction of your bankroll to bet in order to maximize the expected logarithm of wealth — i.e., long-term growth rate.
Where: b = decimal odds − 1 (net odds), p = your estimated win probability, q = 1 − p (loss probability).
Full Kelly maximizes growth mathematically but causes large swings (drawdowns of 50%+ are common). Most professional bettors use Half Kelly or Quarter Kelly to reduce variance while still capturing most of the growth benefit.
The Kelly formula is only as good as your win probability estimate. Overestimating your edge leads to overbetting and ruin. Always err on the conservative side when estimating your probability.
In 2026, the biggest Kelly mistake on sportsbooks is treating same-game parlays or “bet builder” legs as independent. They’re usually strongly correlated, so a standard Kelly stake can be far too large even when the displayed odds look generous. Practical fix: if two or more legs depend on the same game script or player usage, calculate your edge on the full combined price only, then bet no more than 25-50% Kelly. This matters even more now that books auto-boost SGP payouts while quietly widening hidden hold.