Kelly Criterion Calculator
Size a bet from your bankroll, the odds on offer and your own estimate of the chance of winning.
Odds are entered in decimal format. Use the odds converter for American or fractional prices. Results are estimates for planning, not advice.
How it works
The Kelly formula is f = (b × p − q) ÷ b, where b is the decimal odds minus one, p your estimated chance of winning and q the chance of losing. It returns the fraction of your bankroll that maximises long-run growth, and zero when you have no edge.
Worked example
At odds of 2.20 with a 50% chance of winning, your edge is 10% and full Kelly says 8.33% of bankroll. Half Kelly, the more common choice, is 4.17%: a 41.67 stake from a 1,000 bankroll.
The catch
Kelly is only as good as your probability estimate. Overestimate your edge and it tells you to bet far too much, which is why most bettors use a half or a quarter. If the calculator says "no bet", the price is not good enough for the chance you gave it.