Free calculator
Kelly Criterion Calculator
Full Kelly is only optimal if your probability is exactly right. It never is — which is why this caps at 5% of bankroll.
How to use it
Change any input and the results update immediately. The values are also written into the address bar, so you can bookmark a calculation or paste the link to someone else and they will see exactly the same numbers.
Everything here computes with the same functions that produce the grades inside WeBall, so a number on this page will never contradict a number on a bet card.
What the term means
A staking formula that sizes each bet to the size of its edge, maximising long-run bankroll growth.
Kelly answers 'how much', given that you already know a bet is good. The full formula is f = (bp − q) / b, where b is the net decimal odds, p your win probability and q its complement. A 55% chance at even money suggests staking 10% of bankroll.
Full definition of kelly criterion →
Learn the math behind it
A calculator is faster than doing this by hand, but knowing why the formula works is what lets you spot when a number is wrong. Read the full guide →