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Expected Value (EV) in Sports Betting: Formula & Calculator
By Odds Reference Published March 4, 2026 Updated July 19, 2026 Editorial Policy
Expected value (EV) measures how much a bet profits or loses on average if you placed it many times over. A positive EV means the bet is profitable long-term; a negative EV means it loses money over time, regardless of any single outcome. EV is the core metric that separates disciplined, profitable 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, but Kalshi and Polymarket both charge trading fees that trim the edge slightly
- Long-term profitability requires consistently finding and betting +EV situations, sized appropriately with a tool like the Kelly Criterion
How Do You Calculate Expected Value?
The EV formula has two components: how much you profit when you win, weighted by your win probability, minus how much you lose when you lose, weighted by your loss probability. The result is the average dollar outcome per bet if you repeated the wager many times, not what happens on any single bet.
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. Run any specific bet through the Odds Reference EV calculator to skip the manual arithmetic.
What Does a +EV Bet Look Like?
A +EV bet exists when your estimated win probability exceeds the odds’ implied probability. Estimating a 55% chance an NBA team covers a -110 spread (implied 52.4%) creates a 2.6-point edge, which turns a $100 bet into +$5.00 of expected value per bet — a real long-run advantage even though any single wager can still lose.
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?
A -EV bet exists when your estimated probability sits at or below the odds’ implied probability. At the same -110 line (implied 52.4%) but a true 50% coin-flip probability, the math flips: that $100 bet loses -$4.55 in expected value on average — the standard house edge built into a -110/-110 market.
- EV = (0.50 x $90.91) - (0.50 x $100)
- EV = $45.45 - $50.00
- EV = -$4.55 per $100 wagered
Every dollar bet at true 50/50 loses 4.55 cents on average against a -110/-110 market. That is the vig at work.
How Does EV Change Across Different Odds and Probabilities?
EV rises as your estimated probability moves further above the odds’ implied probability, and falls as it moves below. The table below shows EV per $100 wagered across five true-probability levels and five American-odds lines, making the breakeven threshold and profit magnitude visible at a glance.
| 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. Convert any American, decimal, or fractional line to its implied probability first with the odds converter before running your own numbers through this table.
Why Are Most Bets Negative EV?
Most bets are -EV because sportsbooks build a margin into every line. On a standard -110/-110 spread, both sides imply 52.4%, for a combined 104.8% — an in-built 4.8-point cushion the book collects regardless of outcome. Beating that margin consistently requires a genuine edge, not just a hunch.
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. Compare current lines across the market on the Odds Reference dashboard before assuming a number is soft.
Our expected value gambling guide walks through EV calculation in detail with additional examples across casino games, parlays, and multi-leg picks. If a stretch of -EV bets is becoming hard to walk away from, the responsible gambling toolkit and the National Council on Problem Gambling (1-800-522-4700) are free resources built for exactly that.
How Does EV Apply to Prediction Markets?
Prediction market contracts make EV easier to estimate because the price is already an implied probability. A contract trading at 40 cents implies a 40% chance; if your research suggests the true probability is 55%, that 15-percentage-point gap converts directly into expected value once you account for the (small) trading fee.
- 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, before fees
That 15-cent edge per dollar risked is substantial even after costs. Kalshi, a CFTC-regulated exchange, charges roughly 1-2 cents per contract on entry and exit, while Polymarket charges about 2% of net winnings at settlement — both far lighter than sportsbook vig. Our prediction market fees guide breaks down the exact math, and the fee calculator applies it to any trade size. (Fee figures last verified July 19, 2026.)
For more on how prediction market pricing works, see the prediction markets glossary. Track live contract prices across exchanges on the Odds Reference dashboard before sizing a position.
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. Because closing lines are the market’s most efficient price, consistently beating them is the most reliable proxy for +EV without knowing the true probability.
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. In practice, you never know the true probability with certainty, which is exactly why CLV is a useful stand-in metric.
How Should You Use EV in Practice?
Using EV in practice means estimating a probability, converting the odds to their implied probability, comparing the two, and sizing the resulting edge appropriately. Skipping any one of these steps — especially the probability estimate — turns the formula from a real edge calculation into a guess dressed up in math.
- 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.