Expected Value (EV) & Kelly Criterion
Compute the expected value of a bet based on your own win probability and stake. You can optionally calculate a Kelly Criterion stake recommendation.
Learn how EV works | Learn how Kelly sizing works
Expected Value (EV) and Kelly Criterion Explained
Expected Value (EV) is the average amount you can expect to win or lose per bet over the long run. A positive EV (+EV) bet means you're expected to profit over time, while a negative EV (-EV) bet means you'll lose money in the long run. The EV formula is: EV = (Win Probability × Profit) - (Loss Probability × Stake). For example, if you bet $100 at +150 odds with a 50% win probability, your EV is (0.50 × $150) - (0.50 × $100) = $25. This means on average, you expect to win $25 per bet.
The Kelly Criterion takes EV a step further by determining the optimal bet size to maximize long-term bankroll growth while minimizing risk of ruin. The formula is: Kelly % = (Win Probability × Decimal Odds - 1) / (Decimal Odds - 1). Full Kelly can be aggressive, so many bettors use fractional Kelly (e.g., 0.25 or 0.5 Kelly) for more conservative bankroll management. Kelly sizing ensures you bet more when you have a larger edge and less when the edge is small.
This calculator computes both EV and recommended Kelly stake in one place. Enter your estimated win probability, the odds you're getting, and your stake to see if you have a +EV bet. Optionally, input your bankroll and Kelly fraction to calculate the optimal bet size. Use this tool to identify value bets and manage your bankroll scientifically.