What is expected value (EV) in sports betting?

Expected value is the average amount a bet wins or loses if the same bet is placed many times over. It is the one number that says whether a price is worth taking. It says nothing about whether any single bet wins.

Written by Jesse, NegativeEV. Last updated 12 August 2026.

How is the EV of a bet calculated?

EV compares the true probability of an outcome to the probability the price implies.

Written out: EV = (true win probability x the profit if it wins) - (true loss probability x the amount staked). If the true chance is higher than the price implies, the bet is positive EV. If it is lower, the bet is negative EV.

The formula is the easy part. Getting an honest true probability is the hard part, because the sportsbook's own price is not it.

A boost changes the payout but not the formula, so whether a boost is really a deal is the same comparison at a better price.

What does negative EV mean?

A negative EV bet loses money on average, even though it sometimes wins.

The price is shorter than the real chance of the outcome justifies. A negative EV bet can still win. It is still a bad bet, because a bet is judged by the price paid, not by how one night turned out.

Why are most bets negative EV?

Every sportsbook builds a margin into its prices - the rake it keeps for taking the bet. It tilts the average bet against the bettor before any handicapping starts.

On player props and thin markets, where the books themselves are least certain, the gap between the price and the real probability tends to be widest. Measured across a full board, most of the bets on offer grade negative EV.

How can a bet's EV be checked before it is placed?

Compute the true probability from a model of the game itself, then compare it to the price.

NegativeEV simulates each game thousands of times, play by play, to produce a true win probability for any bet, then reports the expected value at the quoted odds. Ten free checks a day, unlimited when signed in.

What does an EV number not tell you?

It does not tell you what happens tonight.

EV is a long-run average. A positive EV bet loses often. A negative EV bet wins often. The number describes the price, not the outcome.

It is also only as good as the true probability behind it. A bet that cannot be matched to a simulated game comes back ungraded rather than guessed at.

More on negative EV: what negative EV means.