Kelly Criterion Calculator 2026
Calculate optimal bet sizing based on your edge and probability estimates
Enter Bet Parameters
Kelly Results
Enter odds, probability, and bankroll to see optimal stake
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Kelly Criterion Formula
The mathematics behind optimal bet sizing
Kelly Formula
b=1.5, p=55%, q=45% → f* = (1.5×0.55 - 0.45) / 1.5 = 25%
Edge Calculation
2.50 odds × 45% prob = 1.125 - 1 = 12.5% edge
Expected Value
EV = (2.50 × 0.45 × $100) - (0.55 × $100) = +$57.50
Where:
- f* = fraction of bankroll to bet
- b = decimal odds - 1 (net payout)
- p = probability of winning
- q = probability of losing (1 - p)
How Kelly Criterion Works
Calculate Your Edge
Compare your estimated win probability against the implied probability from odds. If your estimate is higher, you have positive edge.
Apply Kelly Formula
The Kelly formula determines the optimal fraction of your bankroll to wager based on your edge and the odds offered.
Use Fractional Kelly
Most professionals use Half Kelly (50%) or Quarter Kelly (25%) to reduce variance while maintaining growth.
Maximize Growth
Kelly Criterion maximizes long-term bankroll growth rate. Overbetting beyond Kelly actually decreases expected growth.
Kelly Fraction Comparison
Impact of different Kelly fractions on your betting
| Kelly Fraction | Growth Rate | Variance | Ruin Risk |
|---|---|---|---|
| Full Kelly | Maximum | High | Moderate |
| Half Kelly | 75% of max | Medium | Low |
| Quarter Kelly | 50% of max | Low | Very Low |
Pro Tips for Kelly Betting
Use Half Kelly
Full Kelly is mathematically optimal but has high variance. Half Kelly provides 75% of the growth with much lower drawdowns.
Be Honest About Probability
Kelly is only as good as your probability estimates. Overconfidence leads to overbetting and potential ruin.
Track Your Edge
Keep records of your bets to verify if your probability estimates are accurate over time. Adjust if needed.
Kelly sizing works best with sound strategy — understand the EV of splitting 10s before sizing your bets
Frequently Asked Questions
About the Kelly Criterion Calculator
The Kelly Criterion calculator helps bettors determine the mathematically optimal stake size for bets with positive expected value. Developed by John Kelly Jr. at Bell Labs in 1956, this formula has been used by legendary investors like Warren Buffett and professional gamblers worldwide.
Unlike flat staking or percentage systems, Kelly dynamically adjusts bet size based on your edge. Bigger edge means bigger bet. This approach maximizes long-term bankroll growth while managing risk. Our calculator supports Full Kelly, Half Kelly, and Quarter Kelly fractions.
This tool is 100% free, calculates in real-time as you type, and requires no registration. Updated for 2026 with the latest bankroll management best practices used by professional sports bettors.
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Evgeny Volkov
Verified ExpertOver 10 years developing software for the gaming industry. Advanced degree in Mathematics. Specializing in probability analysis, RNG algorithms, and mathematical gambling models.