Expected Value (EV)

Expected value is the single number that decides whether a bet is worth making. It is the sum of each possible outcome multiplied by its probability. A 10 stake at decimal odds of 3.00 on an outcome with a true 40% chance has an expected value of 0.40 times 20 profit minus 0.60 times 10 stake, giving plus 2.00: a positive-EV bet. Change the true chance to 30% and the same price becomes negative EV.

The concept matters because it separates process from result. A positive-EV bet can lose, and often will, while a negative-EV bet can win; only over a large sample does expectation dominate variance. Serious bettors therefore judge decisions by EV rather than by profit and loss, and use closing line value as a proxy because true probabilities are unobservable. For operators the same maths runs in reverse: every priced market is designed to carry negative expectation for the customer, and bonus terms are modelled so that the expected cost of the offer stays below the expected value of the player acquired.