Definition
Expected value is the average profit or loss you would expect if the same bet were placed over and over again under identical conditions. A positive expected value bet is often written as +EV. A negative expected value bet is -EV.
Formula
EV = (Probability x Decimal Odds) - 1
If the result is greater than zero, the bet has positive expected value.
Example
Suppose you believe a team has a 55% chance of winning and the bookmaker offers decimal odds of 2.00. The calculation is:
(0.55 x 2.00) - 1 = 0.10
That means the bet has +10% expected value. It may still lose on the day, but the price is favorable enough to be profitable over a large sample.
Why EV matters more than picking winners
Many bettors judge every wager by whether it wins or loses. Professionals judge bets by whether the price was right. Winning a bad price does not prove skill. Losing a strong +EV bet does not mean the process was wrong.
Related terms
- Overround and vig explain how bookmaker margin reduces value.
- Closing line value helps confirm whether your EV process is beating the market.
- Bankroll discipline matters because even strong EV can experience long losing streaks.