calculators · Updated 21 Jun 2026
Kelly Criterion Calculator
Enter the decimal odds, your estimated chance of winning, and your bankroll. The calculator returns the Kelly-optimal stake along with safer fractional-Kelly amounts.
Full Kelly maximises long-term growth but is volatile. Most bettors use a fraction (0.25–0.5×) to cut drawdowns and absorb estimate error.
How it reads
- Full Kelly is the mathematically growth-maximising stake — but only if your win probability is exactly right. It is deliberately aggressive.
- Half and quarter Kelly scale that stake down. They give up a little long-term growth in exchange for much smaller swings, which matters because your probability estimate is never perfect.
- No edge? If the odds are shorter than your probability justifies, the Kelly fraction is zero or negative and the right stake is nothing.
For the full reasoning behind the formula — and why full Kelly is usually too aggressive in practice — read the Kelly criterion guide. To size stakes sensibly across a whole season, pair it with sound bankroll management.
Related
Frequently asked questions
How do I calculate the Kelly stake?
Kelly fraction = (decimal odds × win probability − 1) ÷ (decimal odds − 1). Multiply that fraction by your bankroll to get the stake. If the result is zero or negative, the bet has no edge and Kelly says stake nothing.
Why use half or quarter Kelly instead of full Kelly?
Full Kelly maximises long-term growth but only if your probability estimate is exactly right. Since real estimates carry error, full Kelly is volatile and can overbet. Half or quarter Kelly keeps most of the growth with far smaller swings, which is why most disciplined bettors use a fraction.
What happens if my edge is negative?
The Kelly fraction comes out at zero or below, meaning the price is shorter than your probability justifies. The correct stake is nothing — there's no value to back.