Educational use only. This calculator is for educational purposes. It models expected values but cannot predict outcomes. Gambling involves risk and modelled results do not guarantee any return.
Expected Value Calculator
Enter decimal odds and your estimate of true probability to compute the modelled expected value of a single bet.
How to Use This Calculator
Decimal odds are the format used by Australian bookmakers. Odds of 2.50 mean you receive $2.50 for every $1 staked (including your stake back), a profit of $1.50. Odds of 1.80 are shorter; odds of 5.00 are longer.
True probability is your estimate of the real likelihood that the selection wins. This is the hard part: the calculator cannot compute this for you. You need an independent estimate of the true probability, which differs from the implied probability the bookmaker’s odds embed. The gap between your estimated true probability and the bookmaker’s implied probability is where positive EV either exists or does not.
The bookmaker’s implied probability is: 1 / decimal odds. At odds of 2.50, implied probability is 40%. If your independent estimate is 50%, the EV is positive. If your estimate is 38%, the EV is negative.
Worked Example
Suppose a horse is offered at $2.50 (decimal odds). Your analysis suggests the horse has a 50% true win probability.
- Decimal odds: 2.50
- True probability: 50%
- EV% = (2.50 x 0.50) - 1 = 1.25 - 1 = 0.25 = 25%
- EV per $100 staked = $25.00
A 25% positive EV means that on average, for every $100 staked on bets with these parameters, the modelled return is $125. Individual bets still win or lose; the expected value is a long-run average concept. A single bet at 25% EV still loses roughly 50% of the time.
Where True Probability Comes From
The calculator requires you to supply an independent true probability estimate. Without a reliable estimate, the EV output is only as good as your input. Three common sources:
- Your own form analysis. Study the race, the runners, the track, and the conditions to form a view on each runner’s winning probability. This approach is slow and expertise-dependent.
- Market-derived estimates. Use the betting exchange price (Betfair) as a proxy for market consensus, which removes the bookmaker’s overround. Betfair prices are a reasonable starting point but not a definitive truth.
- A signal tool. Tools like EVSTREAM compute EV signals for AU racing by comparing bookmaker prices against an independently calibrated model. This is the fastest source of a credible true probability estimate for AU racing.
For a full explanation of the EV formula and how to find positive-EV bets in AU racing, see the EV betting Australia guide.
Understanding the Output
The calculator shows two outputs:
EV% is the expected return as a percentage of the stake. A 10% EV on a $50 stake means the modelled long-run gain is $5 per bet on average.
EV$ per $100 staked scales the expected value to a $100 stake for easier comparison across different odds levels.
A positive EV% does not mean the next bet wins. It means that over many repeated bets with the same edge, the average outcome is profitable. Short sequences of losing bets are entirely consistent with a positive-EV strategy. Variance is inherent.
Related Reading
- What is EV betting?: the conceptual foundation
- EV betting Australia guide: AU-specific context, legal status, account management
- Kelly criterion calculator: sizing a single EV bet against your bankroll
- Dutching calculator: splitting a stake across multiple positive-EV selections
- EVSTREAM review: AU racing EV signal tool with independent probability estimates
For the true probability signal that powers the EV calculation in practice, see EVSTREAM. For how we evaluate EV signal tools in our comparison universe, see our scoring methodology.