This Kelly calculator sizes a stake in proportion to your edge. Give it the odds, your chance, your bankroll and a Kelly fraction, and it shows the Kelly percentage and the stake in pounds.
If the odds don’t beat your estimate, it shows “No bet”: Kelly never stakes anything without an edge.
Kelly stake calculator
Key points
- Kelly % = (b × p − q) ÷ b, where b = odds − 1 and q = 1 − p.
- Half and quarter Kelly shrink the stake to allow for errors in p.
- If Kelly % is zero or below, there is no bet.
Using the calculator
Enter the decimal odds, your chance as a percentage and your betting bankroll, then choose full, half or quarter Kelly.
The calculator shows the Kelly percentage of your bankroll and the stake. Your bankroll should be money set aside for betting that you can comfortably afford, kept apart from bills and savings.
Worked example
Worked example
The odds are 3.00, you rate the chance at 37% and your bankroll is £600, so b = 2.00 and q = 0.63.
Kelly % = (2.00 × 0.37 − 0.63) ÷ 2.00 = 0.11 ÷ 2.00 = 5.5%. That makes full Kelly £33.00, half Kelly £16.50 and quarter Kelly £8.25.
Now lower your chance to 31%. The sum becomes (0.62 − 0.69) ÷ 2.00 = −3.5%, so the calculator shows “No bet”.
Reading the results
Kelly assumes your chance is exact, and it never is. If you overrate your chances, full Kelly stakes too much and the swings become large, which is why most people use half or quarter Kelly, or simple flat stakes. Our Kelly criterion (Lesson 12 out of 25 in the Masterclass) guide covers the trade-offs.
A Kelly stake doesn’t make a bet more likely to land. It only sizes the stake to an edge you believe you have.
Before you trust a Kelly stake
Check the edge first with the expected value calculator, then use the betting variance calculator to see how much a bankroll can swing. For the original idea, see the Wikipedia page on the Kelly criterion.
Related guides and calculators
- Kelly criterion: how much to stake
- Bankroll management (Lesson 11 out of 25 in the Masterclass)
- All betting calculators
18+ only. Betting should stay fun. Set a budget before you start, only bet what you can comfortably afford, and take a break whenever you need one. For free, confidential support, visit BeGambleAware.org or call the National Gambling Helpline on 0808 8020 133.