Expected Value (+EV) Calculator
Enter the odds you're offered and the true chance of the outcome (as fair odds or a win %). The tool returns the expected value per unit and, optionally, the expected profit on your stake.
Fill in the fields above to see the result.
Expected value is what a bet returns on average if you could repeat it forever. It says nothing about the next game. It says everything about the next season.
How the math works
The calculator weighs what you win by what you believe the real chance of winning is, and subtracts what you lose by the rest:
EV per unit = p × (odds − 1) − (1 − p)
Where p is the true probability of the outcome, by your estimate, and odds − 1 is the net profit per unit staked. Multiply by your stake and you get EV in money.
There is a shortcut that reaches the same verdict: the fair odds are 1 ÷ p. If the odds you took are higher than the fair odds, EV is positive. If lower, negative. The full formula is for knowing by how much.
Worked example
Three bets that look nothing alike, all with the same expected value:
| Odds | Your true prob | Fair odds | EV per unit | EV on 100 |
|---|---|---|---|---|
| 2.10 | 50.0% | 2.00 | +5.0% | +5.00 |
| 3.00 | 35.0% | 2.857 | +5.0% | +5.00 |
| 1.50 | 70.0% | 1.429 | +5.0% | +5.00 |
| 1.95 | 50.0% | 2.00 | −2.5% | −2.50 |
The first three are the same bet in EV terms, even though one wins 7 times in 10 and another 3.5 in 10. This is why strike rate does not measure skill: the 1.50 favourite will look like genius and the 3.00 longshot like a disaster, and both are earning the same 5%.
The fourth row is the same probability as the first with 7% less price. Seven percent of odds turns into ten percentage points of EV, from +5% to −2.5%. That is how a bad price eats an edge.
Where it misleads
**The p is yours, and that is where the error lives.** The formula is trivial arithmetic; the entire difficulty is estimating the true probability. If your p comes from a hunch, the EV you get is a hunch with decimal places.
A screen price is not a fair price. Using the bookmaker's own implied probability as p always returns negative EV the size of the margin, because you would be comparing a price against itself. Strip the vig first, or use a sharper book's line as the reference.
Positive EV is not money in hand. At +5% EV you still lose most of your 3.00 bets. EV only shows up in the ledger after a large sample, and staking more than your bankroll can absorb takes you out before then.
FAQ
Where do I get the true probability?
The most practical route is to use the price of a sharp, liquid market, with the vig removed, as your estimate of p. If the book you bet at offers more than that, the difference is your value. Your own model works too, but it needs validating before it becomes money.
Does positive EV mean I will win this bet?
No. It means the price is on your side. A 3.00 bet with positive EV loses 65% of the time and is still the right decision every single time.
How much should I stake when EV is positive?
In proportion to the edge and to your bankroll, not to your enthusiasm. The Kelly calculator does that sizing from the same p and the same odds.
To get a defensible p, start with the no-vig calculator. The value betting guide covers the whole line of reasoning. Betting is entertainment for adults 18 and over and carries a risk of loss.