Expected value (EV) in sports betting
Expected value is the only number that separates math-based bettors from guessers. Here's the short answer first, then the formula, then how to find +EV bets without a spreadsheet.
Short answer
Expected value (EV) is the average profit per dollar staked if you made the same bet forever at the same price. If EV is positive, the bet makes money on average (+EV). If it's negative, it loses (-EV). Single-bet outcomes are noise; EV is signal.
The EV formula
EV = (true win % × profit if won) − (true loss % × stake)
Three inputs: your true win probability, your potential profit, and your stake. The first one is where bettors go wrong — they use the sportsbook's implied probability, which already includes vig.
Worked example
You bet $100 on a team at +150. The devigged market says the team's true win probability is 45%.
- Profit if won: $150
- EV = (0.45 × $150) − (0.55 × $100) = $67.50 − $55.00 = +$12.50
- Edge: +12.5% per dollar staked. Strong +EV.
How to find the "true" probability
Use the market itself. Take the implied probability of both sides of a two-way market, add them (they'll sum to ~104–108% because of vig), then scale each back so the total is 100%. That scaled number is the market's fair probability — the closest free proxy for true probability.
The EV calculator does this in one input. The Bet Analyzer pulls live consensus across every major US sportsbook so you don't have to.
Why EV beats hot takes
A 60% win rate on -200 favorites is -EV. A 30% win rate on +400 dogs is +EV. Win rate alone tells you nothing — only price-vs-probability does. That's the entire engine behind every grade on AiOddsLab.
Frequently asked questions
What is expected value (EV) in sports betting?
Expected value is the average profit or loss per dollar staked if you placed the same bet thousands of times at the same price. A +EV bet returns money on average; a -EV bet loses money on average. Single outcomes are random, but EV is the only number that matters over a full season.
How do you calculate expected value on a bet?
EV = (true win probability × profit if won) − (true loss probability × stake). Example: a +150 bet ($100 stake → $150 profit) with a true 45% win probability has EV = (0.45 × 150) − (0.55 × 100) = 67.50 − 55 = +$12.50 per $100 staked, a +12.5% edge.
Where do I get the 'true probability' to calculate EV?
Devig the live market. Take the implied probabilities from both sides of the same market across major books, sum them (they'll exceed 100% because of vig), then scale each back so they total 100%. The scaled number is the market's consensus fair probability — the closest free estimate of the true line.
How much edge do I need before a bet is +EV?
Any positive edge is +EV mathematically. In practice, sharp bettors target 2%+ edge to outrun variance and book limits. 5%+ is rare and strong. Sub-1% edges get eaten by closing line movement and rounding error.
Is an expected value calculator accurate?
An EV calculator is only as accurate as the fair-odds input. Use a devigged consensus across multiple sportsbooks (not a single book) for the truest read. AiOddsLab's analyzer pulls live market prices automatically so you don't have to do it by hand.
Why do sportsbooks let +EV bets exist?
Mispricing happens constantly — slow line updates, promo boosts, stale player props, and books targeting recreational money. Sharp bettors who find +EV consistently get limited or banned, which is why most +EV opportunities are short-lived.