Quick answer: Expected value (EV) is the average amount a bet would return per stake if you could place it many times over. This calculator works it out for you: enter your own estimated probability of the outcome, the decimal odds on offer and your stake, and it returns the bet's expected value. A positive number means the bet is priced in your favour over the long run; a negative number means it is priced against you.
What is expected value in betting?
Expected value is a long-run average, not a prediction of the next result. It answers a single question: if this exact bet, at these exact odds, were repeated a very large number of times, what would the typical return per stake be? Any individual bet still wins or loses in full — EV only describes the pattern across a large sample.
The idea comes straight from probability theory, where the expected value of an outcome is each possible result multiplied by its probability, summed together. In betting there are two outcomes that matter: the bet wins (you collect your profit) or it loses (you forfeit your stake).
The expected value formula
For a single bet at decimal odds, expected value per unit staked is:
EV = ( P(win) × profit if it wins ) − ( P(lose) × stake )
Written per £1 staked, where p is your estimated win probability and odds are decimal:
EV per £1 = ( p × (odds − 1) ) − ( 1 − p )
The key input is your own probability estimate. The calculator does the arithmetic, but the quality of the answer depends entirely on how good that estimate is. If your probability is just the odds turned back into a percentage, EV will always come out at roughly zero minus the bookmaker's margin — by definition. EV only becomes positive when your estimate is genuinely more accurate than the price.
How to use this calculator
- Enter your estimated probability of the outcome, as a percentage. This is your view of how likely the result is — from a model, from the no-vig price, or from your own analysis.
- Enter the decimal odds currently offered on that outcome. If you have fractional or American odds, convert them first with the odds converter.
- Enter your stake. The tool shows EV both as a cash figure for that stake and as a percentage of it.
- Read the result. A positive EV means the price is in your favour on this estimate; a negative EV means it is not. Zero means the odds exactly match your probability.
Worked example
Suppose you estimate a team's chance of winning at 45% (0.45), the decimal odds are 2.50, and you stake £10.
- Profit if it wins = £10 × (2.50 − 1) = £15
- EV = ( 0.45 × £15 ) − ( 0.55 × £10 ) = £6.75 − £5.50 = +£1.25
- As a percentage of stake: +£1.25 ÷ £10 = +12.5%
So on this estimate the bet carries a positive expected value of £1.25 per £10 staked. That does not mean this particular bet returns £1.25 — it wins £15 or loses £10. It means that, across many bets priced like this and estimated this accurately, the average return would be positive. Change the probability to 40% (which is what odds of 2.50 imply before margin) and the EV falls to £0 — the edge came entirely from your estimate being higher than the market's.
Positive EV vs negative EV
A positive-EV (+EV) bet is one where your estimated probability is higher than the probability the odds imply. A negative-EV (−EV) bet is the reverse. Because bookmakers add a margin (the "vig"), the average bet at the offered price is slightly negative EV before you bring any information of your own. Finding positive EV is therefore about having a more accurate probability than the price reflects, not about the size of the odds.
Expected value vs a value bet
The two are closely linked but answer different questions. A value bet check tells you whether a bet has an edge and how big that edge is as a percentage. Expected value tells you how much that edge is worth in cash for a given stake. If a bet is a value bet, its EV is positive; the EV calculator puts a number on it. Use the value-bet calculator to screen, and this one to size the reward.
Limitations to keep in mind
- EV is only as good as your probability. A wrong estimate produces a confident but meaningless number. Calibrate your inputs against a reliable source such as the no-vig market price.
- It says nothing about variance. A positive-EV approach can still lose over a run of bets. Staking method (for example the Kelly criterion) manages that risk; EV does not.
- Prices move. The EV you calculate is for the odds at the moment you check. Tracking closing line value is a better long-run test of whether your estimates beat the market.
Frequently asked questions
What does a positive expected value mean?
It means that, on your probability estimate, the odds are priced in your favour, so the average return per stake across many identical bets would be positive. A single such bet still wins or loses in full.
How do you calculate the expected value of a bet?
Multiply your win probability by the profit if it wins, then subtract your loss probability multiplied by the stake: EV = (p × profit) − ((1 − p) × stake). Per £1 staked this is (p × (odds − 1)) − (1 − p).
What is a good EV percentage in betting?
There is no fixed threshold, and small edges are the norm rather than large ones. What matters more is that your probability estimates are well calibrated, because an inflated estimate produces a large but false EV.
Can a bet have positive EV and still lose?
Yes. Expected value is a long-run average. Over a small number of bets, results can swing well away from it in either direction; that is variance, not a flaw in the estimate.
Where do I get the probability to enter?
Common sources are a prediction model, the no-vig market price (the odds with the bookmaker margin removed), or your own analysis. The no-vig calculator is a good neutral starting point.
Is expected value the same as expected profit?
For a single bet, the EV figure this calculator shows for your stake is the expected profit or loss on that bet. Expressed as a percentage it is the expected return per unit staked.
Why is my EV negative when I use the bookmaker's own odds as the probability?
Because the offered odds include the bookmaker's margin. Turning them straight back into a probability bakes that margin in, so EV lands slightly below zero. Positive EV requires an estimate that is more accurate than the priced-in one.
Sources
- Expected value (probability theory) — en.wikipedia.org/wiki/Expected_value
- KiqIQ methodology — how KiqIQ estimates probabilities
For education only. KiqIQ provides probability estimates, not betting advice or guaranteed outcomes. 18+. If gambling stops being fun, support is available at BeGambleAware.org.