MLB
NFL
NBA
NHL
EPLWhat Is the Kelly Criterion?
The Kelly Criterion is a mathematical formula designed to maximize long-term bankroll growth by calculating the optimal percentage of your funds to wager on a given bet. It balances risk and reward by factoring in your perceived edge and the odds offered. Popularized by John Kelly in 1956, it’s a staple for sharp bettors and quantitative traders.
The Kelly Formula Explained
The formula is:
$$ f^* = \frac{bp - q}{b} $$
Where: - $ f^* $: Fraction of your bankroll to bet - $ b $: Decimal odds - 1 (e.g., +200 = 2.0) - $ p $: Probability of winning - $ q $: Probability of losing (1 - p)
Example with American Odds
Suppose you believe the New York Yankees have a 60% chance to win a game at +200 odds (decimal: 3.0). Plugging into the formula:
$$ f^* = \frac{(3.0 * 0.6) - 0.4}{3.0} = \frac{1.8 - 0.4}{3.0} = 0.466 $$
Kelly recommends betting 46.6% of your bankroll. However, this is often considered too aggressive.
Why Full Kelly Can Be Too Aggressive
While full Kelly maximizes growth, it assumes infinite time and perfect edge estimation. In reality, overbetting—even with correct probabilities—increases drawdown risk. For example, the Kelly-derived 46.6% stake in our example could lead to rapid bankroll erosion if the Yankees underperform.
Practical Application: Half and Quarter Kelly
Most bettors use half Kelly (23.3% in our example) or quarter Kelly (11.6%) to reduce variance while still capitalizing on value. This approach is particularly effective in volatile markets, as seen in AI-driven Kalshi prediction bots that use Quarter-Kelly for risk management.
When to Use the Kelly Criterion
- High-confidence bets with clear edges
- Parlays or round robins to manage risk across multiple outcomes (see Round Robin Betting Explained)
- Long-term strategies where compounding matters
Avoid Kelly in short-term scenarios or when edge estimation is uncertain. Always back-test with historical data before deploying it in live betting.
Final Thoughts
The Kelly Criterion is a powerful tool, but it’s not a magic bullet. Use it in conjunction with robust bankroll management and adjust stakes based on your risk tolerance. For advanced strategies, explore how AI systems like Kalshi bots apply modified Kelly models to prediction markets.