Expected Value (EV)

Expected value (EV) is the average amount you can expect to win or lose on a bet if you could repeat it an infinite number of times. Positive EV (+EV) means the bet favours you. Negative EV (-EV) means it favours the house. Almost every casino bet is -EV.

The formula is straightforward: multiply each possible outcome by its probability, then add them all up. A coin flip bet that pays $2 on heads and loses $1 on tails has an EV of ($2 x 0.5) + (-$1 x 0.5) = +$0.50. That's a bet you'd want to take all day long.

In casino games, EV is negative because of the house edge. A $10 bet on European roulette's red has an EV of roughly -$0.27 (the 2.7% house edge applied to your bet). Over a few spins that's noise. Over 10,000 spins? The house collects. Understanding EV is what separates players who know they're paying for entertainment from players who think they've found a system.