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The Kelly Criterion is a mathematical formula used to calculate the optimal bet size to maximise long-term bankroll growth.
It tells you what percentage of your bankroll to stake based on your estimated probability of winning and the decimal odds offered.
It is only valid when you believe there is a positive expected value (EV). If there is no edge, the result is zero, meaning no bet.
The Kelly formula compares your estimated probability with the bookmaker’s implied probability.
If your probability is higher, you have an edge and the stake increases. If it is lower, the stake becomes zero.
The larger your edge, the larger the recommended stake.
Full Kelly
Uses the full calculated stake. Maximises growth but increases volatility.
Half Kelly
Uses 50% of the calculated stake. Reduces risk and smooths swings.
Most bettors use fractional Kelly for more stable results.
The Kelly Criterion helps you avoid overbetting on small edges and underbetting on strong ones.
It automatically adjusts your stake size based on your advantage instead of emotion or guesswork.
The accuracy of the Kelly Criterion depends entirely on your probability estimate.
If your probability is wrong, the staking recommendation will also be wrong.