Kelly Criterion Helper
Get the ideal stake for your edge and bankroll — full, half and quarter Kelly.
How to Use This Calculator
- Pick the odds format you’re working with (Decimal, Fractional, or American)
- Pop in the odds for your bet
- Add your own estimated chance of winning, written as a percentage
- Tell the calculator your total bankroll
- We’ll show you the Kelly fraction, the suggested stake, and gentler half/quarter Kelly options too
Formula
Kelly Criterion Formula:
f* = (bp - q) / b
Where:
- f* = fraction of bankroll to wager
- b = decimal odds - 1 (net profit per dollar)
- p = probability of winning
- q = probability of losing (1 - p)
Expected Value = (p x b) - q
Frequently Asked Questions
So what exactly is the Kelly Criterion?
It’s a maths formula that works out the best bet size to grow your bankroll as much as possible over the long run, all while steering you clear of going broke.
Do I have to stake the full Kelly amount every time?
Not at all. A lot of seasoned bettors stick to fractional Kelly (half or quarter) to smooth out the bumps. Going full Kelly can give you big swings even when your edge is genuine.
What's it telling me when the Kelly value comes out negative?
A negative Kelly number means the bet has negative expected value. In plain terms, skip it — placing it would cost you money over time.
How precise does my probability guess need to be?
Very. The Kelly formula reacts strongly to your probability estimate. Overstate your edge and you’ll overbet, which is exactly why fractional Kelly is suggested as a built-in safety cushion.