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Kelly Criterion Calculator
Calculate optimal bet sizing for maximum bankroll growth
Enter Your Parameters
Enter odds like -110 or +150
%
Your honest estimate of win probability
Recommended Bet Size
$55.00
5.50% of bankroll
Analysis
Full Kelly %5.50%
Adjusted Kelly %5.50%
Expected Value5.00%
Edge5.00%
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Kelly Criterion assumes accurate probability estimates. Most professionals use Half Kelly or less to account for estimation errors.
Understanding Kelly Criterion
The Kelly Criterion is a mathematical formula for optimal bet sizing that maximizes long-term bankroll growth. Developed by John Kelly at Bell Labs in 1956, it balances risk and reward based on your edge.
The Formula
f* = (bp - q) / b
- f* = Fraction of bankroll to wager
- b = Net odds (decimal - 1)
- p = Probability of winning
- q = Probability of losing (1 - p)
Why Use Fractional Kelly?
- Estimation Error: Your win probability is an estimate. Half Kelly provides a buffer for being wrong.
- Reduced Variance: Full Kelly can have significant drawdowns. Fractional Kelly smooths returns.
- Psychological Comfort: Smaller bet sizes are easier to stick with during losing streaks.
- Professional Standard: Most successful bettors use 25-50% of full Kelly.
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