Kelly Criterion Calculator
Calculate optimal bet sizing for investments and gambling. Maximize geometric bankroll growth while minimizing ruin risk.
About
Serious investors and professional bettors understand that identifying an edge is only half the battle. The other half is money management. The Kelly Criterion is a mathematical formula used to determine the optimal size of a series of bets. It balances the probability of winning against the payout odds to maximize the logarithm of wealth. Betting too little leaves money on the table while betting too much guarantees eventual bankruptcy due to variance.
This tool calculates the exact percentage of your capital to deploy on a specific opportunity. It includes options for "Fractional Kelly" which allows for a more conservative approach. This reduces volatility while still growing the bankroll at a mathematically proven rate.
Formulas
The optimal fraction f* of the bankroll to wager is given by the formula:
Where b is the net odds received on the wager (Odds - 1), p is the probability of winning, and q is the probability of losing (1 − p).
Reference Data
| Win Probability | Decimal Odds | Edge (%) | Kelly Stake (%) | Half Kelly (%) |
|---|---|---|---|---|
| 55% | 2.00 | 10% | 10.0% | 5.0% |
| 60% | 1.90 | 14% | 15.5% | 7.7% |
| 50% | 2.10 | 5% | 4.5% | 2.2% |
| 33% | 3.50 | 15.5% | 6.2% | 3.1% |
| 10% | 15.00 | 50% | 3.6% | 1.8% |
| 90% | 1.05 | -5.5% | 0.0% | 0.0% |
| 50% | 2.00 | 0% | 0.0% | 0.0% |
| 75% | 1.50 | 12.5% | 25.0% | 12.5% |