Kelly Criterion Calculator
Work out the mathematically optimal stake size for a bet given your edge and bankroll.
Full Kelly stake
100.00
Half Kelly stake
50.00
Quarter Kelly stake
25.00
Full Kelly is mathematically optimal for long-run growth but very volatile. Most professional bettors use half or quarter Kelly to reduce variance.
FAQs
What is the Kelly Criterion?
A formula for sizing bets that maximizes long-run bankroll growth, given your edge (how much better your estimated win probability is than the odds imply) and the payout odds. Bet too little and you leave growth on the table; bet too much and variance can wipe you out.
Why use half or quarter Kelly instead of full Kelly?
Full Kelly assumes your probability estimate is exactly right. In practice estimates have error, and full Kelly is highly volatile — fractional Kelly sacrifices some growth rate for meaningfully less variance, which is why most professional bettors use it.
What happens if my probability estimate is wrong?
The whole calculation depends on it — if your estimated win probability is too optimistic, Kelly will recommend staking more than your real edge justifies, which is the single biggest practical risk of using this formula.