Kelly Criterion Calculator
Determine the optimal bet size to maximize your bankroll growth. The Kelly Criterion helps you balance profit potential against risk of ruin.
Kelly Criterion Calculator
Enter odds and probability to calculate optimal stake size
Accepts decimal (2.50), American (+150, -200), or fractional (5/2) odds
Understanding the Kelly Criterion
What is the Kelly Criterion?
The Kelly Criterion is a mathematical formula that determines the optimal size of a series of bets. It balances the competing forces of maximizing growth while minimizing the risk of losing your entire bankroll.
The Formula
f* = (bp - q) / bWhere:
- • f* = Fraction of bankroll to bet
- • b = Net odds received (decimal odds - 1)
- • p = Probability of winning
- • q = Probability of losing (1 - p)
Full Kelly
Betting the full Kelly amount maximizes expected bankroll growth, but can lead to significant volatility and drawdowns.
Fractional Kelly
Most bettors use 1/4 or 1/2 Kelly. This sacrifices some growth for much smoother bankroll progression and reduced risk.
Common Kelly Scenarios
| Odds | Your Prob | Full Kelly | 1/4 Kelly | On £1000 |
|---|---|---|---|---|
| 2.00 | 55% | 10.0% | 2.5% | £25 |
| 2.50 | 45% | 12.5% | 3.1% | £31 |
| 3.00 | 40% | 10.0% | 2.5% | £25 |
| 1.80 | 60% | 33.3% | 8.3% | £83 |
| 4.00 | 30% | 10.0% | 2.5% | £25 |
Kelly Criterion Best Practices
- •Start Conservative: Use 1/4 or 1/2 Kelly when starting out. Full Kelly can be too volatile for most bettors.
- •Be Honest with Probabilities: The Kelly Criterion is only as good as your probability estimates. Track and refine them over time.
- •Simultaneous Bets: If placing multiple bets at once, reduce individual stakes as the combined risk increases.
- •Avoid Negative Kelly: If the calculation returns zero or negative, there's no edge—don't place the bet.
- •Maximum Stake Limit: Many bettors cap Kelly stakes at 5-10% of bankroll regardless of what the formula suggests.
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