What is expected value in betting?
Expected value (EV) is what a bet returns on average if you could repeat it infinitely many times. It is the only number that decides whether a bet is worth making: not whether it wins today, but whether the price pays more than the real risk.
The formula is EV = (p × profit) − (q × stake), where p is your probability of winning, q the probability of losing, and profit is stake × (odds − 1).
Implied probability: what the odds are really saying
Every set of odds carries an implied probability: 1 / decimal odds. Odds of 2.00 imply 50%. Odds of 4.00 imply 25%. The bet has value when your estimate is higher than that implied number — and only then.
💡 Careful: the implied probability from the odds includes the bookmaker's margin, so the whole market adds up to more than 100%. That margin is exactly what you have to beat.
Positive EV does not mean you win
A +EV bet can lose, and it will lose often. Value shows up over hundreds of bets, not over one. That is why it goes hand in hand with staking: knowing a bet has value tells you to place it, and the Kelly calculator tells you how much.
How to use this calculator
- Enter the decimal odds. If your bookmaker uses another format, convert them in the odds converter.
- Estimate the real probability of the outcome. Be conservative: an inflated estimate turns a losing bet into an apparently winning one on paper.
- Enter the stake you would put on it.
- The calculator returns the EV in absolute terms and as a percentage of the stake.