Kelly Criterion Calc
Ideal stake from edge and bankroll — full, half, quarter Kelly.
How to Use This Calculator
- Pick your odds format (Decimal, Fractional, or American)
- Punch in the odds for your bet
- Drop in your estimated win probability, written as a percentage
- Add your full bankroll
- Read off the Kelly fraction, the recommended stake, and the half/quarter Kelly alternatives
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 exactly is the Kelly Criterion?
It’s a mathematical formula that pinpoints the ideal bet size to grow your bankroll as fast as possible over the long haul while keeping you clear of going broke.
Should I go all-in on the full Kelly stake?
Most seasoned bettors dial it back to fractional Kelly (half or quarter) to tame the swings. Full Kelly can throw up wild ups and downs even when your edge is real.
What's a negative Kelly value telling me?
A negative Kelly value flags a bet with negative expected value. Skip it — over time, that wager bleeds money.
How precise does my probability estimate have to be?
Kelly is brutally sensitive to your probability input. Inflate your edge and you’ll overbet — which is precisely why fractional Kelly is the smart safety buffer.