Calculate the expected value of a bet from decimal or American odds and your win probability, and check whether it is a value bet with a positive edge.
Betting Expected Value Formula and Method
EV = stake × (entered win probability × decimal odds − 1)
Use a win probability estimated independently of the offered price. Expected value weights the win profit and full-stake loss by their probabilities. For example, a fifty-percent estimate at decimal 2.2 gives ten units of expected net profit on a hundred-unit stake.
How to Use This Calculator
Choose the odds format, then enter the odds and your win probability. Check the selected record, unit and scoring conventions before calculating. Review the primary result and its breakdown, then open the calculation steps to see how the inputs were used.
Worked Example
With the example inputs in the table, the result is 10 USD. Expected value is an average over hypothetical repeated trials.
Input and Example Guide
| Input or category | Example or weight | Entry guidance |
|---|---|---|
| Odds format | Decimal | Choose Decimal or American odds. |
| Stake | 100 | Use the stated unit; retain available precision. |
| Offered odds (decimal) | 2.2 | Use the stated unit; retain available precision. |
| Your win probability (%) | 50 | Use the stated unit; retain available precision. |
Interpreting the Result
The estimate can be positive while the individual ticket loses. Its interpretation concerns a hypothetical average under the entered probability, which itself can be wrong. This two-outcome model assumes ordinary cash-stake settlement without draws returning stakes, partial wins, fees or promotional conditions.
The entered probability drives the estimate. A positive estimate is not a prediction that this wager will win; settlement assumes one win-or-loss cash stake.
Assumptions and Common Input Errors
Expected value is an average over hypothetical repeated trials. Keep the same currency and settlement conditions throughout a scenario. Displayed currency amounts are rounded to two decimals; calculations retain precision unless cent allocation is explicitly described.
Saving and Revising a Scenario
A successful calculation is saved in this browser and can be restored on the next visit. Editing an input marks the old result as a previous result so it is not mistaken for an updated calculation. Reset clears the inputs and the saved result.
Sources
Betfair Help, Decimal Odds and Stake-Inclusive Returns, reviewed 2026. Arithmetic and scenario assumptions are specified above.
