Expected Value Betting Calculator
What This Calculator Measures
Compare your estimated win probability with the probability implied by decimal odds.
Enter decimal odds, your estimated probability of winning, and a stake. The calculator shows whether the entered odds produce positive, negative, or approximately break-even expected value based on your probability estimate.
It does not predict the winner of an event and does not generate a win probability. Its output is a mathematical comparison between your estimate and the entered odds.
Calculate Expected Value
Use decimal odds greater than 1.00 and an estimated probability between 0% and 100%.
The result is only as reliable as the probability estimate entered. The calculator does not validate that estimate.
How the Calculation Works
Decimal odds define the market break-even point. Your probability estimate defines your fair price. Expected value converts the relationship between the odds and your probability estimate into an expected profit or loss for the entered stake.
Example: Odds 2.20 at a 48% Estimated Probability
At decimal odds of 2.20, the raw implied probability is 45.45%. If you estimate the outcome at 48%, your probability is 2.55 percentage points above that break-even level.
| Measure | Result | Meaning |
|---|---|---|
| Raw implied probability | 45.45% | The mathematical break-even probability at odds of 2.20. |
| Probability difference | +2.55 pp | Your estimate is above the probability implied by the price. |
| Fair odds | 2.083 | The decimal price corresponding to a 48% probability estimate. |
| Expected profit/loss | +5.60 per 100 staked | The expected average result per 100 staked if the 48% probability estimate is accurate. |
| Expected ROI | +5.60% | Expected profit expressed as a percentage of stake. |
How to Interpret Value Status
- Positive mathematical EV: the entered probability and odds produce an expected ROI above the break-even range.
- Negative mathematical EV: the entered probability and odds produce an expected ROI below the break-even range.
- Approximately break-even: expected ROI is within 0.05 percentage points of zero.
These labels describe only the mathematical relationship between the inputs. They are not a prediction, betting recommendation, or assessment of whether the probability estimate itself is correct.
Limitations
- The estimated probability is an assumption. The calculator cannot determine whether it is accurate or well calibrated.
- Raw implied probability is not a no-vig probability. It is calculated directly from the individual decimal price entered.
- One result does not establish a long-term edge. Expected value describes a mathematical average rather than the outcome of a single event.
- Odds can change. A different market price changes implied probability, expected profit/loss and expected ROI.
- Settlement terms are not modelled. The calculation assumes a standard win-or-lose decimal-odds payoff.
Related Calculators
To calculate the probability expressed by one price without entering your own probability estimate, use the Implied Probability Calculator. To measure bookmaker margin across a complete market, use the Bookmaker Margin Calculator.
FAQ
What probability should I enter?
Enter your own estimated probability that the selected outcome wins. The calculator does not create or verify that estimate.
What does raw implied probability mean?
It is the probability obtained directly from the entered decimal odds using 1 divided by the odds. It does not remove bookmaker margin from a complete market.
Can positive mathematical EV still lose?
Yes. Positive mathematical EV describes an expected average under the probability assumption entered. An individual event can still lose.
Does a higher stake change expected ROI?
No. Stake changes the expected profit or loss amount, but expected ROI remains the same when the odds and probability estimate are unchanged.
Does this calculator recommend bets?
No. It performs a mathematical comparison between decimal odds and the probability estimate entered by the user.