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Kelly criterion calculator
The Kelly criterion is a formula for how much of your bankroll to stake when you think a price is too big. It stakes more when your edge is bigger and nothing when there's no edge. Enter the odds and your own estimate of the chance.
Full, half and quarter Kelly
Full Kelly grows a bankroll fastest in theory, but only if your estimates are right. Most people who use Kelly stake a fraction of it, often a quarter or a half, because a small error in the estimate makes full Kelly stakes far too big.
Your edge is how much you expect to make per £1 staked if your estimate is right. If it's zero or negative, Kelly says don't bet.
The Kelly formula
Stake share = (b × p − q) ÷ b. Here b is the decimal odds minus 1, p is your chance of winning and q is your chance of losing (1 minus p).
At 2/1 (3.0) with a 40% chance, b is 2, so (2 × 0.4 − 0.6) ÷ 2 = 0.1. Full Kelly stakes 10% of your bankroll. Quarter Kelly stakes 2.5%.
Kelly stakes at 2/1
| Your chance | Edge | Full Kelly | Full Kelly stake | Quarter Kelly stake |
|---|---|---|---|---|
| 34% | +2.0% | 1.0% | £10.00 | £2.50 |
| 36% | +8.0% | 4.0% | £40.00 | £10.00 |
| 40% | +20.0% | 10.0% | £100.00 | £25.00 |
| 45% | +35.0% | 17.5% | £175.00 | £43.75 |
| 50% | +50.0% | 25.0% | £250.00 | £62.50 |
Moving your estimate from 36% to 40% more than doubles the stake. That's why fractional Kelly is safer: your estimate is a guess, and Kelly trusts it completely.
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Read the guide: The Kelly criterion explainedRead →Questions people ask
What is the Kelly criterion in betting?
A formula that sets your stake as a share of your bankroll, based on the odds and your estimate of the true chance. John Kelly published it in 1956.
Should I use full Kelly?
Most people shouldn't. Full Kelly can halve your bankroll in a bad run even when you have a real edge, and if you overestimate your chances it overbets. Half or quarter Kelly is much steadier.
Why does Kelly say stake nothing?
Your estimated chance is no better than the chance the odds imply. With no edge, the best stake is zero.