Expected value (EV) calculator

Expected value (EV) is the average amount you would win or lose per bet if you placed the same bet many times. A positive EV (+EV) bet is one where the odds offered are higher than the true fair odds, giving you a mathematical edge over the bookmaker. Professional bettors focus exclusively on finding and placing +EV bets.

The formula is: EV = Stake x (Probability x (Odds - 1) - (1 - Probability))

For example, if you believe an outcome has a 52% chance of winning and the odds are 2.10 with a 10 unit stake: EV = 10 x (0.52 x 1.10 - 0.48) = 10 x 0.092 = 0.92 units expected profit per bet.

Edge is expressed as: Edge = (Probability x Odds) - 1. An edge of 3% means that for every unit staked, you expect to profit 0.03 units on average. While individual bets are unpredictable, the law of large numbers means your results will converge toward the expected value over many bets. Use the variance simulator to understand how many bets are needed for your edge to become visible.

Once you know a bet is +EV, the next question is how much to stake. The Kelly criterion answers this: it calculates the stake that maximises long-term bankroll growth based on your edge and odds. Most professional bettors use fractional Kelly (typically 25-50%) to reduce variance while still exploiting their edge.