Expected value (EV)

The average outcome of a bet if it were repeated many times: probability of winning times profit, minus probability of losing times stake.

BetG8 Editorial · Reviewed November 6, 2026 · Not betting, legal or investment advice

Buying a Yes share at 40 cents that you believe has a 50 percent chance has an EV of 0.5 × 0.60 - 0.5 × 0.40 = +0.10, ten cents per share. The same share at 55 cents has negative EV for you. Positive EV does not mean the bet wins; it means that over many similar bets you expect to come out ahead.

Sportsbook bets are negative EV for the average customer because of vig. Prediction market trades are closer to zero-sum between traders, minus fees, so positive EV requires being better informed than the other side.

EV is the yardstick; Kelly turns it into a stake size.

Where you will see it on BetG8

Kelly criterion Vig

More strategy terms

Kelly criterion Brier score Calibration Favorite-longshot bias Arbitrage Hedge Take profit and stop loss Bankroll management

Frequently asked questions

What does "Expected value (EV)" mean?: The average outcome of a bet if it were repeated many times: probability of winning times profit, minus probability of losing times stake.
Why does expected value (ev) matter for prediction markets?: EV is the yardstick; Kelly turns it into a stake size.