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Expected Value Calculator: Calculate EV for Any Bet or Trade
Last Updated: March 4, 2026
Expected value quantifies whether a bet or trade is profitable over the long run. The calculator above takes your probability estimate and the offered odds, then outputs the EV per unit wagered. Positive EV means the math favors you. Negative EV means it favors the house. Every serious bettor and trader uses this calculation before committing capital.
How Do You Use the EV Calculator?
Enter two inputs: the odds being offered (in any format) and your estimated true probability of the outcome occurring. The calculator returns the expected value per bet, your edge as a percentage, and whether the wager is +EV or -EV.
The odds input determines the payout structure. Your probability input is the variable that decides whether value exists. If the implied probability from the odds is 55% and you estimate 60%, the calculator shows a +EV result. If you estimate 50%, it shows -EV.
The quality of your probability estimate determines the quality of the output. The formula is precise; the art is in the probability assessment.
What Does an EV Calculation Look Like in Practice?
Consider an NFL spread at -110, which implies 52.4%. You model the game and estimate the team covers at 57%.
| Input | Value |
|---|---|
| Odds | -110 (American) |
| Implied Probability | 52.4% |
| Your Estimated Probability | 57.0% |
| Stake | $100 |
| Profit if Win | $90.91 |
| EV Calculation | (0.57 x $90.91) - (0.43 x $100) |
| Expected Value | +$8.82 per $100 bet |
| Edge | +4.6 percentage points |
Over 500 bets at this edge, you would expect roughly $4,410 in profit. Any single bet might lose, but the accumulated edge compounds into a measurable return.
Now flip the scenario. Same -110 line, but your estimate is only 50% — a coin flip:
| Input | Value |
|---|---|
| Your Estimated Probability | 50.0% |
| EV Calculation | (0.50 x $90.91) - (0.50 x $100) |
| Expected Value | -$4.55 per $100 bet |
That -$4.55 is the standard house edge on a -110 market. This is the cost of the vig on every bet placed without an edge.
How Does EV Differ Between Sportsbooks and Prediction Markets?
The formula is identical. The inputs change.
At a sportsbook, you must first convert the odds to implied probability (removing the vig for accuracy). The vig inflates the implied probability, so your true estimate must clear a higher bar.
In prediction markets, the contract price is the implied probability. A contract at $0.40 means 40%. If you believe the true probability is 52%, the EV is:
- Cost: $0.40 per contract
- Payout if correct: $1.00
- Profit if correct: $0.60
- EV = (0.52 x $0.60) - (0.48 x $0.40) = $0.312 - $0.192 = +$0.12 per contract
That 12-cent edge per contract represents a 30% return on the $0.40 cost. Because prediction markets carry minimal vig, the bar for finding +EV trades is lower than at sportsbooks — but the market is also more efficient at pricing liquid events.
The Odds Reference dashboard tracks thousands of prediction market prices and sportsbook lines. Comparing implied probabilities across both verticals is the most direct way to identify where one market may be mispricing an outcome relative to the other.
How Does EV Connect to Bet Sizing?
EV tells you whether to bet. It does not tell you how much. A +EV bet with a 1% edge and a +EV bet with a 10% edge both deserve capital, but not the same amount.
The Kelly Criterion translates EV into optimal bet size. The formula is: Kelly % = Edge / Odds. A 5% edge at +100 odds suggests risking 5% of your bankroll. A 5% edge at +300 odds suggests a smaller percentage because the variance is higher. Use the Kelly calculator to size positions automatically.
Most practitioners use fractional Kelly (half or quarter Kelly) to reduce volatility. The EV calculator gives you the edge; Kelly tells you how to deploy it. Together, they form a complete framework for disciplined wagering.
What Mistakes Invalidate an EV Calculation?
The formula itself is simple. Errors come from the inputs:
- Overestimating your probability. If you think every bet is 60% when the true rate is 52%, your EV calculations will show phantom edges that do not exist. Track your calibration over hundreds of bets.
- Using raw implied probability instead of no-vig. The odds -150 imply 60%, but the true market price (after vig removal) might be 57%. Using 60% sets a higher bar than the book actually believes. Always calculate no-vig probability for a fair comparison.
- Ignoring correlation. EV calculations assume independent outcomes. If you are stacking multiple positions on correlated events, the combined EV is not the sum of individual EVs.
The EV calculator handles the math. The discipline is in honest probability estimation and consistent application across hundreds of decisions.
Key Takeaways
- EV = (win probability x profit) - (loss probability x stake) — positive means long-term profit
- Your edge is the gap between your estimated probability and the implied probability from the odds
- Prediction markets simplify EV analysis because the contract price is the implied probability
- EV determines whether to bet; the Kelly Criterion determines how much
- Accurate probability estimation is the hard part — the formula is the easy part