Guide
How to calculate expected value (EV) on a bet
Expected value (EV) tells you whether a bet is profitable on average. EV = (probability of winning × profit if you win) − (probability of losing × stake). If your estimate of the true probability is higher than the odds imply, the bet is +EV — profitable over the long run even if any single bet loses. Here's the formula, a worked example, and how to find your edge.
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The formula
EV = (P_win × profit) − (P_lose × stake). Convert the odds to their implied probability, compare it to YOUR estimate of the true probability, and if your number is higher, the gap is your edge. Positive EV means the bet wins money on average; negative EV means it loses over time.
A worked example
Say a sportsbook offers +120 (implied ~45.5%) on an outcome you believe is genuinely 55% likely. On a $100 stake: EV = (0.55 × $120) − (0.45 × $100) = $66 − $45 = +$21. That's a +EV bet — over many similar bets you'd expect to profit, even though plenty of individual ones lose.
Where your edge comes from
+EV requires a probability estimate better than the market's. Sources of edge: line-shopping for the best price, reacting faster than the book, or using sharper probabilities — prediction-market prices are a strong, low-margin reference. Then size stakes sensibly (don't bet your whole bankroll on one edge) and track results to confirm the edge is real.
FAQ
What is a +EV bet?
A bet whose expected value is positive — it makes money on average because your estimated probability of winning is higher than the odds imply. Individual bets still lose; the edge shows up over many bets.
How do I know the 'true' probability?
You estimate it — and your edge is only as good as that estimate. Deep, liquid prediction-market prices are a strong reference because they map to probability with little house margin. Compare them to the sportsbook's implied probability.
Does +EV guarantee I'll win?
No. +EV means profitable on average over the long run, not on any single bet. Variance is real, so bankroll management matters as much as finding the edge.