This Kelly calculator sizes a stake in line with your edge. You give it the odds, your win chance, your bankroll and a fraction, and it shows the Kelly % and the stake in £.
If the odds do not beat your estimate, it says “No bet”. In other words, Kelly never stakes anything without an edge.
Kelly stake calculator
The short version
- Kelly % = (b × p − q) ÷ b, where b = odds − 1 and q = 1 − p.
- Half and quarter Kelly cut the stake to allow for errors in p.
- If Kelly % is zero or less, there is no bet.
How to use the Kelly calculator
Enter the decimal odds, your win chance as a %, and your betting bankroll. Then pick full, half or quarter Kelly.
The Kelly calculator shows the Kelly % of your bankroll and the stake. Your bankroll should be money you can afford to lose, kept apart from bills and savings.
Worked example
Worked example
The odds are 2.50, you rate the chance at 44%, and your bankroll is £500. So b = 1.50 and q = 0.56.
Kelly % = (1.50 × 0.44 − 0.56) ÷ 1.50 = 0.10 ÷ 1.50 = 6.7%. Full Kelly is therefore £33.33, half Kelly is £16.67 and quarter Kelly is £8.33.
Now drop your chance to 38%. The sum gives (0.57 − 0.62) ÷ 1.50 = −3.3%, so the calculator shows “No bet”.
What the result means
Kelly assumes your win chance is exact, but it never is. If you overrate your chances, full Kelly stakes too much and the swings get large. That is why most people use half or quarter Kelly, or simple flat stakes. Our guide to the Kelly criterion covers the trade-offs.
Also, a Kelly stake does not make a bet more likely to win. It only sizes the stake to an edge you believe you have.
Before you trust a Kelly calculator 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
18+ only. Betting should be fun, and every bet can lose. Set a budget you can afford to lose and stick to it. For free, confidential support, visit BeGambleAware.org or call the National Gambling Helpline on 0808 8020 133.