Kelly Criterion for Sports Betting
Complete Guide to Optimal Bet Sizing
Learn how to use the Kelly Criterion to optimize your bet sizing, maximize long-term profits, and manage risk effectively in sports betting.
What is the Kelly Criterion?
The Kelly Criterion is a mathematical formula developed by John Kelly in 1956 that determines the optimal bet size to maximize long-term growth while minimizing risk. In sports betting, it tells you exactly how much of your bankroll to wager based on your edge and the odds offered.
Why Kelly Criterion Matters
Without proper bet sizing: You might have +EV bets but still lose money by betting too much or too little. The Kelly Criterion solves this by calculating the mathematically optimal bet size for maximum long-term growth.
Think of Kelly as your "bet sizing GPS" - it guides you to the perfect bet amount that maximizes profit while keeping your bankroll safe from ruin. It's especially powerful when combined with positive expected value betting.
The Kelly Criterion Formula
The Formula
Kelly % = (bp - q) / bKelly > 0
Positive edge - bet this percentage of your bankroll
Kelly ≤ 0
No edge or negative edge - don't bet
Fractional Kelly
Bet 25-50% of Kelly recommendation for safety
Real Example
Note: This is full Kelly. Most bettors use 25-50% of this amount for safety.
Full Kelly vs Fractional Kelly: Which Should You Use?
While the Kelly Criterion gives you the mathematically optimal bet size, most successful bettors use fractional Kelly for practical reasons:
Full Kelly Risks
High volatility - large swings in bankroll
Requires perfect probability estimates
Can lead to ruin with estimation errors
Emotionally difficult to handle losses
Fractional Kelly Benefits
Reduced volatility and smoother growth
More forgiving of probability errors
Easier to stick to long-term
Still captures most of Kelly's benefits
Recommended Fractional Kelly Levels
Conservative
25% Kelly
Lowest risk, steady growth
Moderate
50% Kelly
Balanced risk/reward
Aggressive
75% Kelly
Higher growth, more risk
Common Kelly Criterion Mistakes to Avoid
Mistake #1: Overestimating Edge
Being too optimistic about your probability estimates leads to oversized bets and potential ruin.
Mistake #2: Using Full Kelly
Full Kelly is too aggressive for most bettors. Use fractional Kelly (25-50%) for safety.
Mistake #3: Ignoring Correlation
Betting multiple correlated games at full Kelly can lead to overexposure and increased risk.
Mistake #4: Not Adjusting for Bankroll
Kelly assumes you can bet any amount. In reality, you need to consider minimum bet sizes and bankroll constraints.
Mistake #5: Emotional Betting
Letting emotions override Kelly calculations leads to poor bet sizing decisions and losses.
Mistake #6: Not Tracking Results
Without tracking your Kelly bets and results, you can't improve your probability estimates over time.
Try Our Kelly Criterion Calculator
Ready to start using Kelly Criterion for your bets? Our odds calculator includes Kelly sizing recommendations, or you can use our automated EV Picks tool that calculates optimal bet sizes for every opportunity.
Automated Kelly Sizing
Our AI-powered platform automatically calculates Kelly Criterion recommendations for every +EV pick, taking the guesswork out of bet sizing.
Continue Your Learning Journey
What is Positive Expected Value Betting?
Learn the fundamentals of +EV betting and how to identify profitable opportunities before applying Kelly sizing.
How to Find Positive EV Bets
Step-by-step guide to identifying +EV opportunities, including tools, strategies, and common mistakes to avoid.
Ready to Apply Kelly Criterion to Your Betting?
Join thousands of successful bettors who use our AI-powered platform to automatically calculate Kelly sizing for every +EV opportunity, taking the guesswork out of bet sizing.
Complete Your Betting Toolkit
EV Calculator
Calculate expected value and Kelly sizing recommendations for your bets with our free calculator.
Arbitrage Calculator
Find risk-free arbitrage opportunities and calculate optimal stakes for guaranteed profits.
Odds Calculator
Convert between American, Decimal, and Fractional odds with implied probability calculations.