Calculate the mathematically optimal stake size for your bets
The Kelly Criterion is a formula used by professional bettors and investors to determine the optimal stake size. Enter your probability estimate, the odds and your bankroll to see the recommended bet amounts.
Full Kelly
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Recommended Stake
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Half Kelly Stake
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Quarter Kelly Stake
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The Kelly Criterion formula is: Kelly% = (b × p - q) / b, where b is the net odds (decimal odds - 1), p is the probability of winning, and q is the probability of losing (1 - p). It tells you the optimal percentage of your bankroll to stake on a bet with positive expected value.
Most experienced bettors recommend Half Kelly or Quarter Kelly. Full Kelly maximizes long-term growth rate but produces extreme variance and large drawdowns. Half Kelly achieves approximately 75% of the growth rate while dramatically reducing risk. Quarter Kelly is even more conservative and suitable for beginners.
A negative Kelly result means there is no positive edge — the bet has negative expected value. The Kelly Criterion recommends not placing this bet at all. This happens when the implied probability from the odds is higher than your estimated true probability.
The Kelly Criterion is very sensitive to probability estimates. Small errors can lead to significant overbetting. This is another reason to use fractional Kelly (Half or Quarter). If you overestimate your edge by just 5%, Full Kelly could recommend dangerous stake sizes. Conservative Kelly fractions provide a safety margin.
Yes, but with caution. For accumulators (parlays), multiply the individual probabilities and use the combined odds. However, the Kelly stake for accumulators is typically very small because the probability of winning all legs is low. Many professionals avoid using Kelly for accumulators and instead stick to single bets or small multiples.
