What expected value means in betting
Expected value (EV) is the average profit or loss a bet would produce if you could place it an infinite number of times. Any single bet either wins or loses, but EV tells you what happens at scale - and at scale, EV is the only number that matters.
A +EV bet is one whose long-run average outcome is positive. A -EV bet is one whose long-run average is negative. Sportsbooks survive because nearly every market they post is -EV by the amount of their vig. Your job as a bettor is to find the small subset of bets where your estimate of the true probability beats the implied price by more than the vig.
The expected value formula
EV = (probability of winning × profit if you win) − (probability of losing × stake at risk).
Profit is what the sportsbook pays you in addition to your stake - not the total return. Probability of losing is simply 1 minus probability of winning on a two-outcome bet.
- Symbolic: EV = p · W − (1 − p) · S, where p is your true win probability, W is profit on a win, S is stake risked.
- Per-dollar form: EV% = p · (decimal odds − 1) − (1 − p). Useful for comparing bets of different sizes.
Worked example - a +EV bet
Suppose a sportsbook posts an NFL underdog at +150 (decimal 2.50, implied 40%). Your model - or your read on a clear injury news edge - says the true probability is 45%.
On a $100 stake: EV = 0.45 × $150 − 0.55 × $100 = $67.50 − $55 = +$12.50. Per dollar risked, that is a +12.5% edge. Over hundreds of bets at that edge, your bankroll grows even though many individual bets will lose.
Worked example - a -EV bet
A standard NFL spread at -110 implies you must win 52.38% of the time just to break even. If you genuinely have no opinion versus the market (which is the default assumption - the market is usually right), your true win rate is roughly 50%.
EV = 0.50 × $91 − 0.50 × $100 = $45.50 − $50 = −$4.50. That $4.50 per $100 is the vig. Betting random sides on -110 markets bleeds money at a rate of about 4.5% per wager.
Where +EV actually comes from
Real +EV bets exist, but they are scarce and time-sensitive. Most come from one of four sources, in rough order of accessibility for recreational bettors:
- Promotions and odds boosts. A boosted price (e.g. +250 on something the market prices at +200) is often +EV before any handicapping.
- Line shopping. Holding accounts at several books and always taking the best price for the side you want adds 1–3% EV automatically.
- Slow-moving markets and stale lines. Player props and second-tier sports often lag breaking news by minutes - sometimes hours.
- Genuine modeling edge. Beating the closing line consistently in major markets is the highest bar - but the most durable form of edge.
Closing line value (CLV) - the leading indicator
Because results are noisy, you can bet +EV for months and still lose money. CLV solves this. Closing line value is the difference between the price you took and the line at game time. Consistently beating the close by even half a percent is one of the strongest known predictors of long-term profitability - much faster signal than win/loss record.
If you regularly bet -110 lines that close at -120, your average bet was about 2% +EV regardless of whether it won. Track CLV religiously; trust it more than your bankroll over short windows.
Common +EV mirages
Recreational tools often dress up -EV bets in +EV language. Watch for these patterns:
- Recency bias - 'Team X has covered 7 of 10' tells you nothing predictive on its own.
- Trend mining - any large sports database contains thousands of spurious trends at 60%+.
- Cherry-picked samples - 'Home favorites of 3–6 in division games on Sunday Night Football…' is overfit, not insight.
- Pick services. Most touts are not profitable. The few that are rarely sell. Verify long-term audited records, not screenshots.
Frequently asked questions
How do you calculate expected value on a bet? Multiply your estimated win probability by the profit, subtract the probability of losing times the stake. Positive result = +EV.
What is a good EV percentage in sports betting? Most full-time bettors target 1–3% EV per bet across thousands of wagers. Anything claiming 10%+ sustained EV in major markets is almost certainly miscalculated or short-lived.
Does +EV guarantee profit? No. EV is a long-run average. Variance can keep a +EV bettor underwater for months. That is why bankroll management and CLV tracking exist.