Betting Calculators
Kelly Criterion Calculator
Calculate the mathematically optimal bet size based on your edge and bankroll. Maximize long-term growth while managing risk.
How to Use This Calculator
- Select your odds format (Decimal, Fractional, or American)
- Enter the odds for your bet
- Enter your estimated probability of winning (as a percentage)
- Enter your total bankroll
- See the Kelly fraction, recommended stake, and 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 is the Kelly Criterion?
The Kelly Criterion is a mathematical formula that determines the optimal size of a bet to maximize long-term growth of your bankroll while avoiding ruin.
Should I always bet the full Kelly amount?
Most experienced bettors use fractional Kelly (half or quarter Kelly) to reduce variance. Full Kelly can lead to large swings even with a proven edge.
What does a negative Kelly value mean?
A negative Kelly value means the bet has negative expected value. You should not place this bet as it would lose money over time.
How accurate does my probability estimate need to be?
The Kelly formula is very sensitive to probability estimates. Overestimating your edge leads to overbetting, which is why fractional Kelly is recommended as a safety margin.