Betting calculator
Expected Value Calculator
Estimate the expected value of a bet from your stake, decimal odds and your own estimated probability of winning.
Enter stake, odds and estimated chance
Use decimal odds and your own win probability estimate as a percentage.
This example is positive EV based on your probability estimate.
Expected value formula
Expected value compares the possible profit if the bet wins with the possible loss if it loses, weighted by your estimated probability.
Profit if win = stake x (decimal odds - 1)
Expected value = (probability x profit if win) - ((1 - probability) x stake)
EV ROI % = expected value / stake x 100
The probability input is the important part. If your estimate is too optimistic, the result can look better than the real situation.
Worked example
Suppose you stake £10 at decimal odds of 2.50 and estimate the true chance of winning as 45%. The profit if the bet wins is £15. The expected value is £1.25, which is an expected ROI of 12.50%.
That does not mean the bet will win or that profit is guaranteed. It only shows what the calculation says if the probability estimate is accurate.
Responsible use
Expected value is an educational calculation, not a prediction. Variance, bookmaker limits, market rules, settlement errors, inaccurate estimates and bankroll management all matter. Betting always involves risk, and no calculator can remove that risk.
For the plain-English explanation behind the calculation, read What Is Expected Value in Betting?.
Understand the result
How to interpret this calculator
Betting Maths calculators are designed to show the arithmetic behind the inputs you provide. A calculated return, probability, liability or expected value is not a prediction that an event will happen.
Check the assumptions
Results depend on the odds, stakes, commission, place terms or probability estimates entered. If the inputs change, the result changes.
Reproduce the maths
Our methodology explains the core formulas, rounding approach and limitations used across the calculator library.
Read the calculation methodologyUse the result educationally
Real settlement can also depend on bookmaker or exchange rules, non-runners, voids, liquidity, price movement and promotional terms.