Kelly criterion calculator
Expected growth per bet: 0.501% at full Kelly, 0.375% at half Kelly. Staking more than 20.0% makes your bankroll shrink over time.
The formula
For a bet that pays b to 1 with win probability p, the Kelly fraction is f = (bp − q) / b, where q = 1 − p. If the result is zero or negative you have no edge and should not bet.
Why most people bet less
Full Kelly maximises growth only if you know the probability exactly. If you have overestimated your edge, full Kelly overbets and the cost is large. Half Kelly gives up about a quarter of the growth for half the swings, which is why it is the usual choice in practice.
Practise it
Frequently Asked Questions
What does the growth rate mean?
It is the expected log return per bet at that stake. A higher number means your bankroll compounds faster over many bets.
Can Kelly tell me to bet more than 100%?
Not for a simple bet where you can lose your whole stake. The fraction is always below your win probability.
More free tools: Black-Scholes calculator · Expected value calculator · Probability distribution calculator
For education and interview practice only. Not investment advice.