Kelly Criterion Calculator

Calculate the optimal bet size based on your edge and bankroll. The Kelly Criterion maximizes long-term growth while managing risk.

Bankroll ($)

American Odds

Your Estimated Win Probability (%)

What is the Kelly Criterion?

The Kelly Criterion is a mathematical formula that determines the optimal bet size to maximize long-term bankroll growth. It balances the desire to bet big when you have an edge with the need to avoid catastrophic losses.

Fractional Kelly: Most professional bettors use half or quarter Kelly to reduce variance and account for uncertainty in their probability estimates.

Kelly Criterion Strategy Guides

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Master optimal bet sizing with practical examples and fractional Kelly strategies.

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Bankroll Management Guide

Learn unit sizing, risk of ruin, and strategies to protect and grow your bankroll.

This calculator is for informational and educational purposes only. Results should be verified with your sportsbook before placing any wagers. All betting carries risk. Full Disclaimer

How to Use This Calculator

1
Enter Your Bankroll: Input your total betting bankroll (the money dedicated to betting)
2
Enter the Odds: Input the American odds for the bet you're considering
3
Estimate Win Probability: Enter your estimated probability of winning (be honest and conservative)
4
Review Kelly Recommendations: See full Kelly, half Kelly, and quarter Kelly stake amounts

Frequently Asked Questions

What is the Kelly Criterion?

The Kelly Criterion is a mathematical formula that calculates the optimal bet size to maximize long-term bankroll growth. It was developed by John Kelly at Bell Labs in 1956. The formula: Kelly % = (bp - q) / b, where b = decimal odds - 1, p = win probability, q = loss probability.

Why use fractional Kelly (half or quarter)?

Full Kelly maximizes growth but with high variance. Errors in probability estimates can lead to overbetting. Half Kelly (50% of full) reduces variance by 50% while only reducing growth rate by 25%. Quarter Kelly is even more conservative. Most professionals use 25-50% Kelly.

What happens if Kelly suggests 0% or negative?

If Kelly calculates 0% or negative, you don't have an edge - don't bet! A negative Kelly means the bet is -EV (negative expected value). Only bet when Kelly suggests a positive stake, indicating you have a mathematical advantage.

How accurate do my probability estimates need to be?

Kelly is very sensitive to probability estimates. Overestimating your edge by even a few percent can lead to significant overbetting. This is why most bettors use fractional Kelly - it provides a safety margin for estimation errors.

Should I use Kelly Criterion for every bet?

Kelly works best for independent bets with known edges. For correlated bets (same game), you need to adjust. Some bettors use flat betting (same stake) for simplicity. Kelly is most valuable when you have strong conviction in your edge estimate.