Bookmaker Margin Calculator
Calculate Bookmaker Margin
Enter every outcome in a two-way or three-way market to calculate the combined implied probability, market overround and proportional no-vig probabilities. The calculator evaluates the complete market rather than a single price.
Outcome 1
Outcome 2
Outcome 3
Result
| Total implied probability | — |
|---|---|
| Overround | — |
No-vig result by outcome
| Outcome | Entered odds | No-vig probability | No-vig fair odds |
|---|---|---|---|
| — | — | — | — |
Formula
Each decimal price is converted into raw implied probability. The probabilities for every active outcome are then added together.
The calculator proportionally normalises the implied probabilities so that they total 100%.
Two-way market example
Suppose both sides of a two-way market are priced at 1.91. Each price implies approximately 52.36%.
Total implied probability: 104.71%
Overround: 4.71%
No-vig probability: 50.00% for each outcome
No-vig fair odds: 2.00 for each outcome
The entered prices contain more than 100% combined probability. Proportional normalisation removes the excess and returns the outcomes to a 100% total.
Three-way market example
Consider a football 1X2 market priced at 2.10 for the home win, 3.40 for the draw and 3.60 for the away win.
Total implied probability: 104.81%
Overround: 4.81%
Home no-vig probability: 45.43% — fair odds 2.20
Draw no-vig probability: 28.06% — fair odds 3.56
Away no-vig probability: 26.50% — fair odds 3.77
The no-vig probabilities total 100%. They describe a proportional margin-free version of the entered market, not an independent prediction of the match.
How to use the result
Total implied probability shows how much probability is contained in the complete set of entered prices. A total above 100% produces a positive overround. A total below 100% produces a negative result, commonly described as an underround.
Overround measures the difference between the combined implied probability and 100%. It describes the structure of the entered prices and should not be treated as the bookmaker's guaranteed profit.
No-vig probability proportionally rescales the entered outcomes so that their probabilities total 100%. No-vig fair odds are the decimal prices corresponding to those normalised probabilities.
Compare like with like: enter every possible outcome from the same market and preferably use prices from the same bookmaker at the same point in time. A smaller overround means less excess probability across that market, but it does not prove that a particular selection offers value.
For one price only, use the Implied Probability Calculator. If you have your own probability estimate, use the Expected Value Betting Calculator to compare it with the available price.
Limitations
- Every possible outcome from the same market must be entered to calculate the full market total. One price alone can show implied probability but cannot measure the complete market overround.
- The calculator accepts decimal odds. Fractional or American prices can first be converted with the Odds Converter.
- No-vig probabilities use proportional normalisation. Other margin-removal methods can produce different estimates, especially when the prices are highly uneven.
- The calculation does not account for betting limits, liquidity, promotions, account restrictions, settlement rules or future price movement.
- In live markets, the result reflects only the prices entered and can become outdated as soon as those prices change.
FAQ
What is bookmaker overround?
Overround is the amount by which the combined implied probabilities of all possible outcomes exceed 100%. For example, a market totalling 104.8% has an overround of 4.8%.
Can overround be negative?
Yes. If the entered prices produce a combined implied probability below 100%, the calculator shows a negative overround and identifies it as an underround.
Is overround the same as bookmaker profit?
No. Overround describes the relationship between the listed prices. Actual bookmaker profit also depends on stakes, liabilities, price movement, customer behaviour and event results.
Why do no-vig probabilities add to 100%?
Each raw implied probability is divided by the total implied probability of the market. This proportionally normalises the outcomes to a 100% total.
Does a lower overround mean a bet has value?
No. A lower overround describes the overall pricing of the market. Whether one specific price offers value depends on how its break-even probability compares with your estimated probability for that outcome.