Kelly Criterion Betting Calculator
Optimal stake; full, half and quarter Kelly.
How to Use This Calculator
- Set the odds format (Decimal, Fractional, or American)
- Input the odds for the bet
- Input your estimated win probability as a percentage
- Input your full bankroll
- Read off the Kelly fraction, recommended stake, and the half/quarter Kelly variants
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
Define the Kelly Criterion.
The Kelly Criterion is a formula that fixes the optimal bet size to maximize long-run bankroll growth while keeping you clear of ruin.
Is full Kelly always the right stake?
Most seasoned bettors run fractional Kelly (half or quarter) to cut variance. Full Kelly can swing the bankroll hard even when the edge is real.
What is signalled by a negative Kelly value?
A negative Kelly value flags negative expected value. Skip the bet; over time it loses money.
How precise must my probability input be?
Kelly is highly sensitive to the probability you supply. Overstating your edge causes overbetting, which is exactly why fractional Kelly is advised as a buffer.