What is expected value in gambling?
Expected value (EV) is a mathematical concept that describes the average outcome of a bet if it were repeated many times. A negative expected value (-EV) means the bet loses money on average over time. A positive expected value (+EV) means it wins on average.
How EV is calculated
EV equals the probability of winning multiplied by the win amount, minus the probability of losing multiplied by the loss amount. For a coin flip bet where you risk £1 to win £1 at true 50/50 odds, EV is (0.5 × £1) – (0.5 × £1) = £0. A casino game’s house edge makes EV negative for the player: you’re betting at worse than true odds. A 2% house edge on a £10 bet means an EV of -£0.20 per round.
Why EV matters
Every casino game is -EV for the player by design. Understanding this helps set realistic expectations — no system or strategy converts -EV bets into +EV outcomes over time. EV thinking is most valuable for avoiding the worst bets (very high house edge proposition bets) and choosing games where the -EV is smallest (pass line craps, blackjack with basic strategy, European roulette).