What a bet is worth on average if you could make it over and over. This is the number that actually determines whether a bet is worth making — not whether it wins.
EV calculation itself is simple arithmetic. What actually separates a winning bettor from a losing one is the input you can't look up: an honest estimate of how often the bet actually hits. Overestimate your own win rate by even a few points and a bet that looks positive-EV on this calculator is actually negative in reality.
A more reliable starting point than guessing is comparing the posted price to the no-vig fair price — the market's own opinion with the book's margin removed. If you don't have a specific reason to disagree with the market, that fair price is a better probability estimate than most people's gut feel.
We show the fair price and the true edge on every game on the board, every day, free.