No-vig calculator: market margin and normalized odds

From quoted odds to a 100% total

For each decimal price, the implied probability is 1 divided by the odds. Add these probabilities to find the market total. The overround is that total minus 100%. The tool then divides each implied probability by the total, making the normalized probabilities sum to 100%.

Two outcomes both priced at 1.91 each imply about 52.36%, for a total of 104.71% and an overround of 4.71 percentage points. Proportional normalization gives 50% each, equivalent to decimal odds of 2.00.

Include every possible outcome

For a regulation-time three-way market, enter home, draw and away. Leaving out the draw changes the total and makes the calculation describe an incomplete market. Use prices from the same market and moment when you want to examine one bookmaker’s margin.

You can also compare a set of prices collected from different places, but its total then describes that selection of quotes. It does not identify one bookmaker’s overround. A total below 100% is shown as a negative overround rather than silently corrected.

What no-vig odds tell you

Proportional normalization is one way to distribute the quoted margin. It does not prove the true chance of an outcome or remove differences in how a bookmaker prices favourites and long shots. Use it to understand and compare prices, with the original market and time kept alongside the result.