What is expected value (EV)?
Definition and example from our casino glossary.
Definition
Expected value is the average result of a bet if it were repeated many times, calculated by weighting each outcome by its probability.
Expected value is the core tool for judging any gamble. Multiply each possible result by its probability and add the products together. For a 10 bet on red in European roulette, 18 of 37 outcomes win 10 and 19 lose 10, so EV = (18 × 10 − 19 × 10) ÷ 37 = −0.27. That is the 2.70% house edge expressed in money. Casino games have negative EV for the player by design, with rare exceptions such as some promotions or card counting in live blackjack. EV is additive: the expected loss of a session equals the total amount staked multiplied by the house edge. It is also a long-run measure, so individual sessions can deviate sharply. Thinking in EV helps compare games and offers honestly, and it explains why repeated play almost always ends with the operator ahead.