Kelly Criterion Calculator
Optimal stake from edge and bankroll, with full, half and quarter Kelly outputs.
How to Use This Calculator
- Set the odds format input (Decimal, Fractional, or American)
- Input the odds attached to your bet
- Input your estimated win probability, expressed as a percentage
- Input your full bankroll figure
- Read off the Kelly fraction, the 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
How does the Kelly Criterion work?
The Kelly Criterion is a mathematical model that computes the optimal stake size to maximize the long-run growth rate of your bankroll while keeping the risk of ruin off the table.
Is staking the full Kelly amount advisable?
Most seasoned bettors apply fractional Kelly — half or quarter — to dampen variance. Full Kelly can generate severe bankroll swings even when your edge is genuine.
What is the interpretation of a negative Kelly value?
A negative Kelly value signals that the bet carries negative expected value. Skip it: over time, placing it would erode your bankroll.
How precise must my probability estimate be?
The Kelly formula reacts sharply to probability inputs. Inflating your edge produces overbetting, which is precisely why fractional Kelly is advised as a built-in safety margin.