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What Is Expected Value (EV) in Sports Betting?
Last Updated: March 4, 2026
Expected value is the mathematical measure of how much a bet will profit or lose on average over the long run. Every bet has an EV — positive or negative. Positive EV bets generate profit over time. Negative EV bets guarantee losses. Understanding EV separates disciplined bettors from recreational ones.
Key Takeaways
- EV quantifies the average profit or loss per bet across many repetitions
- A bet is +EV when your estimated probability exceeds the implied probability from the odds
- Most sportsbook bets are -EV for the bettor because of the vig
- Prediction market contracts simplify EV calculation — the price is the implied probability
- Long-term profitability requires consistently finding and betting +EV situations
How Do You Calculate Expected Value?
The EV formula has two components: what you gain when you win, weighted by how often you win, minus what you lose when you lose, weighted by how often you lose.
EV = (Probability of Winning x Profit if Win) - (Probability of Losing x Stake)
This can also be written as:
EV = (P_win x Payout - Stake x 1)
Both forms produce the same result. The key input is your estimated true probability — not the implied probability from the odds.
What Does a +EV Bet Look Like?
Suppose you estimate an NBA team has a 55% chance of covering the spread. The line is -110 (standard juice), which implies 52.4%.
Your edge: 55% - 52.4% = 2.6 percentage points.
For a $100 bet at -110 (win $90.91 profit):
- EV = (0.55 x $90.91) - (0.45 x $100)
- EV = $50.00 - $45.00
- EV = +$5.00 per $100 wagered
Over 1,000 such bets, you would expect to profit roughly $5,000. The individual bet might win or lose, but the math favors you systematically.
What Does a -EV Bet Look Like?
Now consider the same -110 line, but your true estimate is only 50% — a coin flip. The book implies 52.4%, so you are on the wrong side of the margin.
- EV = (0.50 x $90.91) - (0.50 x $100)
- EV = $45.45 - $50.00
- EV = -$4.55 per $100 wagered
This is the standard house edge on a -110/-110 market. Every dollar bet at true 50/50 loses 4.55 cents on average. That is the vig at work.
How Does EV Change Across Different Odds and Probabilities?
The following table shows EV per $100 bet at various true probabilities and American odds. Positive values indicate profitable bets.
| True Probability | -200 (implied 66.7%) | -110 (implied 52.4%) | +100 (implied 50.0%) | +150 (implied 40.0%) | +300 (implied 25.0%) |
|---|---|---|---|---|---|
| 40% | -$40.00 | -$23.64 | -$20.00 | +$0.00 | +$60.00 |
| 50% | -$25.00 | -$4.55 | +$0.00 | +$25.00 | +$100.00 |
| 55% | -$17.50 | +$5.00 | +$10.00 | +$37.50 | +$120.00 |
| 60% | -$10.00 | +$14.55 | +$20.00 | +$50.00 | +$140.00 |
| 70% | +$5.00 | +$33.64 | +$40.00 | +$75.00 | +$180.00 |
The pattern is clear: you profit when your true probability exceeds the implied probability, and you lose when it does not. The magnitude of the edge determines how much.
Why Are Most Bets Negative EV?
Sportsbooks set lines so that the implied probabilities across all outcomes exceed 100%. On a standard -110/-110 spread, both sides imply 52.4%, totaling 104.8%. The bettor must overcome that 4.8-point margin to break even.
For a bet to be +EV, the bettor’s probability estimate must exceed the implied probability after the vig. This requires either superior information, better models, or exploiting market inefficiencies — none of which are easy.
The Odds Reference EV calculator lets you calculate expected value for any bet or prediction market trade. Input your probability estimate and the odds to see whether the math favors you.
How Does EV Apply to Prediction Markets?
Prediction markets strip away much of the complexity. A contract trading at $0.40 implies a 40% probability with minimal vig. If your analysis suggests the true probability is 55%:
- Cost per contract: $0.40
- Payout if correct: $1.00
- Profit if correct: $0.60
- EV = (0.55 x $0.60) - (0.45 x $0.40) = $0.33 - $0.18 = +$0.15 per contract
That 15-cent edge per dollar risked is substantial. Because prediction market prices are clean implied probabilities, EV analysis reduces to a single question: is the true probability higher or lower than the current price?
For more on how prediction market pricing works, see the prediction markets glossary.
What Is the Relationship Between EV and Closing Line Value?
Closing line value (CLV) measures whether you consistently beat the final line before an event starts. If you bet a spread at -3 and it closes at -4, you captured a full point of CLV.
CLV matters because closing lines are generally the most efficient prices the market produces. Bettors who consistently beat the close tend to be +EV over time, even if their short-term results fluctuate. CLV is the most reliable proxy for long-term EV that does not require knowing the true probability — which, in practice, you never know with certainty.
How Should You Use EV in Practice?
- Estimate probability — Build or reference a model for the event. Your probability estimate is the single most important input.
- Convert odds to implied probability — Use the implied probability formulas or the odds converter.
- Calculate the gap — If your estimate exceeds the implied probability, the bet is +EV. If not, pass.
- Size appropriately — Feed the edge into the Kelly Criterion to determine how much of your bankroll to risk.
EV is the only metric that determines whether a betting strategy is profitable. Win rate, streak length, and single-game results are noise. EV is the signal.