Kelly Criterion Calculator
Calculate the optimal bet size using the Kelly Criterion formula to maximize long-term profit while managing risk. Our free Kelly Criterion calculator helps you determine the perfect percentage of your bankroll to wager on each bet. No registration required.
Use the free calculator below to calculate your optimal bet size.
Kelly Criterion Calculator
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How It Works
The Kelly Criterion is a mathematical formula that determines the optimal bet size to maximize long-term growth of your bankroll. It balances maximizing returns with managing risk.
Kelly Criterion Formula:
f = (bp - q) / b
Where:
- f = Fraction of bankroll to bet
- b = Decimal odds - 1 (net odds)
- p = Win probability (as decimal, e.g., 0.45 for 45%)
- q = Loss probability = 1 - p
Optimal Bet = Bankroll × f × Kelly Fraction
Example:
If you have $10,000 bankroll, odds of 2.50, and 45% win probability:
- b = 2.50 - 1 = 1.50
- p = 0.45, q = 0.55
- f = (1.50 × 0.45 - 0.55) / 1.50 = 0.0833 (8.33%)
- Optimal Bet = $10,000 × 0.0833 = $833.33
Fractional Kelly:
Many bettors use fractional Kelly (e.g., 0.25 or 0.5) to reduce risk. Quarter Kelly (0.25) is a popular conservative approach.
Kelly Criterion Calculator Examples
Real-world examples of Kelly Criterion calculations for optimal bet sizing.
Example 1: Value Bet with Kelly
Example 2: Conservative Quarter Kelly
Example 3: High Confidence Bet
How to Use the Kelly Criterion Calculator
Enter Your Bankroll
Enter your total betting bankroll amount.
Enter Odds and Win Probability
Enter the decimal odds for your bet and your estimated win probability as a percentage.
Set Kelly Fraction (Optional)
Choose your Kelly fraction. Use 1.00 for full Kelly, 0.25 for quarter Kelly (recommended for most bettors), or 0.50 for half Kelly.
View Optimal Bet Size
The calculator shows the optimal bet size, Kelly percentage, and expected value in real-time.
How the Kelly Criterion Calculator Works
The Kelly Criterion formula calculates the optimal bet size to maximize long-term bankroll growth while minimizing risk of ruin.
Formula:
f = (bp - q) / b
Where:
- f = Fraction of bankroll to bet (Kelly percentage)
- b = Net odds = Decimal Odds - 1
- p = Win probability (as decimal)
- q = Loss probability = 1 - p
Optimal Bet Calculation:
Optimal Bet = Bankroll × f × Kelly Fraction
Expected Value:
EV = (p × Odds) - 1
If EV > 0, the bet has positive expected value.
Important Notes:
- If f ≤ 0, the bet has negative expected value - don't bet!
- Full Kelly (1.00) maximizes growth but has high volatility
- Fractional Kelly (0.25-0.50) reduces risk while maintaining good growth
- Always use accurate win probability estimates for best results
Frequently Asked Questions
The Kelly Criterion is a mathematical formula that determines the optimal bet size to maximize long-term bankroll growth. It balances maximizing returns with managing risk.
Most bettors use fractional Kelly (0.25-0.50) to reduce risk. Full Kelly maximizes growth but has high volatility. Quarter Kelly (0.25) is a popular conservative approach.
If the Kelly percentage is negative or zero, the bet has negative expected value. You should not place this bet as it will lose money in the long run.
The Kelly Criterion is only as good as your probability estimates. Overestimating your win probability will lead to overbetting and increased risk. Be conservative with your estimates.
Kelly Criterion works best for bets with positive expected value. For negative EV bets, the formula will recommend not betting. Always verify your probability estimates are accurate.
Yes, our Kelly Criterion calculator is completely free to use. No registration required, no hidden fees.