Quick answer: Expected value, often shortened to EV, measures the average profit or loss per dollar wagered on a bet, given its probability of winning. A +EV bet (positive expected value) makes money on average over a large sample. A -EV bet loses money on average. The formula: EV = (Probability of Winning × Net Win) – (Probability of Losing × Stake). Sharp bettors only place +EV bets, even when individual results swing in losses or wins.
The Formula in Practice
Suppose your model says a bet has 60% probability of winning at -110 odds. To win $100 you risk $110. EV calculation: (0.60 × $100) – (0.40 × $110) = $60 – $44 = +$16 per $110 staked. That’s a 14.5% EV per bet. Over a 100-bet sample, average expected profit is $1,600. The actual result will swing wildly due to variance, but the long-run expectation is positive. -EV bets work the same way in reverse: a 50% probability bet at -120 has -2% EV, meaning you lose 2 cents per dollar staked over a long sample.
Why +EV Compounds Over Time
+EV is the only sustainable approach to long-term profit in sports betting. Books advertise the dream of one big win, but the math heavily favors them on every individual bet. The only way to overcome that is to consistently identify mispriced lines and hammer them. PropsBot’s High ROI Signal across 101,881 graded MLB props posts 31.7% verified ROI by doing exactly this: isolating bets where our model probability exceeds the no-vig probability by enough to overcome vig and variance.
The Practical Test for Identifying +EV Bets
First, you need a probability model that’s better-calibrated than the market. The benchmark is Brier score against the Vegas closing line. PropsBot’s MLB Brier (0.1903) beats Vegas (0.1947), which is the gold standard of predictive accuracy in sports forecasting. Without a calibrated model, you can’t reliably find +EV. Second, you need a way to convert that probability into a no-vig comparison. The PropsBot No-Vig Calculator (propsbot.ai/tools/no-vig-fair-odds-calculator) does this automatically. Third, you need bankroll discipline to ride out the variance.
Common Misconceptions About +EV
First mistake: thinking +EV bets always win in the short term. Variance crushes short samples. A +5% EV bet over 50 bets can show a loss due to bad variance, even though the long-run expectation is positive. Second: believing every sharp bettor is +EV. Most aren’t. The market is competitive enough that finding consistent +EV requires real model edge. Third: confusing +EV with sharp money. Sharp money signals where smart bettors are placing wagers, but it doesn’t tell you whether those bets are +EV at the price you can get.
Frequently Asked Questions
What does +EV mean in betting?
Positive expected value. A bet that makes money on average over a long sample, accounting for its probability of winning and the price you got. EV = (P_win × Net Win) – (P_lose × Stake).
How do you calculate the EV of a bet?
EV = (Probability of Winning × Amount You’d Win) – (Probability of Losing × Amount You’d Stake). If the result is positive, the bet is +EV. If negative, it’s -EV.
Are +EV bets guaranteed to win?
No. Individual bets are subject to variance. A +EV bet might lose. The math only works over a large sample, typically 100+ bets at the same edge level.
How does PropsBot identify +EV bets?
We compare our model’s calibrated probability against the no-vig probability of the book line. When our probability exceeds the no-vig probability by enough to overcome vig and variance, the bet is flagged for the High ROI Signal.
What sample size do you need to verify +EV?
Roughly 100 bets at consistent edge level for a meaningful statistical signal. Larger samples (1,000+) reduce variance noise dramatically. PropsBot has 218,826+ graded props, which is statistically significant by any standard.
Part of the PropsBot.AI Sports Betting Glossary. Updated 2026-05-04.
