Kelly Criterion Tool
Find the optimal stake from your edge and bankroll — full, half and quarter Kelly.
How to Use This Calculator
- Pick an odds format: Decimal, Fractional, or American
- Type in the odds for your bet
- Type in your estimated win probability as a percentage
- Type in your full bankroll
- Read off the Kelly fraction, the suggested stake, and the half/quarter Kelly options
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
What does the Kelly Criterion do?
It’s a formula that pins down the optimal bet size for maximizing long-run bankroll growth without risking going broke.
Do I always stake the full Kelly amount?
Most seasoned bettors stick to fractional Kelly (half or quarter) to cut variance. Full Kelly can swing your bankroll hard even when your edge is real.
What's the meaning of a negative Kelly value?
A negative result flags a bet with negative expected value. Skip it — it loses money over the long run.
How precise does my probability estimate have to be?
Kelly reacts sharply to your probability input. Overstate your edge and you overbet, which is exactly why fractional Kelly exists as a buffer.