Bookmaker Margin Calculator

How the Bookmaker Margin Calculator Works

Bookmakers convert each set of decimal odds into an implied probability. In a fair market, the probabilities of every possible outcome add up to exactly 100%. When the total is above 100%, the difference is the bookmaker margin, also known as the overround.

What Is Bookmaker Margin?

Bookmaker margin is the percentage by which the combined implied probabilities of all outcomes exceed 100%. A lower margin generally means the bookmaker is offering more competitive prices on that market.

Two-Way Market Margin

For a market with two possible outcomes, convert both decimal odds into implied probabilities and add them together. The formula is: (100 / Outcome 1 odds) + (100 / Outcome 2 odds) − 100. For example, odds of 1.90 and 1.90 produce a market percentage of 105.26% and a bookmaker margin of 5.26%.

Three-Way Market Margin

Three-way markets, such as a football 1X2 market, include three possible outcomes. The formula is: (100 / Outcome 1 odds) + (100 / Outcome 2 odds) + (100 / Outcome 3 odds) − 100. Odds of 2.10, 3.40 and 3.40 produce a market percentage of 106.44% and a margin of 6.44%.

Fair Odds Without Bookmaker Margin

Fair odds, also called no-vig odds, estimate the price of each outcome after removing the bookmaker margin. This calculator uses proportional normalisation: each implied probability is divided by the total market probability so that all outcomes add up to exactly 100%, then converted back into decimal odds.

How to Read the Result

A market percentage of 100% represents a zero-margin market. Values above 100% show the bookmaker's overround. Fair odds are a margin-free reference price derived from the entered market, not a prediction of the actual result. If the combined percentage is below 100%, the calculator will show a negative margin, which can occur when comparing the best prices across different bookmakers and may indicate an arbitrage opportunity.