Betting Margin Calculator
Enter the odds for each outcome in a match to calculate the bookmaker's margin and fair odds for each selection.
What is Bookmaker Margin?
Every bookmaker builds a margin (also called the overround or vig) into their odds. This margin ensures they make a profit over the long term regardless of the outcome. Understanding margin helps you identify which bookmakers offer the most competitive prices and spot where value might exist.
How Margin Works
In a perfectly fair market (zero margin), the implied probabilities of all outcomes would add up to exactly 100%. In practice, bookmaker odds add up to more than 100% - the excess is the margin. A typical Premier League match has a margin of around 5-7% at most bookmakers, though this varies significantly between sites and markets.
For example: Home win at 2.10 (implied probability 47.6%), Draw at 3.40 (29.4%), Away win at 3.50 (28.6%). Total implied probability = 105.6%. Margin = 5.6%. This means for every 100 staked across all outcomes, the bookmaker expects to keep 5.60 on average.
Fair Odds
The fair odds shown by this calculator represent what the odds would be at zero margin, calculated by adjusting each implied probability proportionally. Comparing fair odds to actual bookmaker odds tells you which outcomes a bookmaker rates more or less highly than the market average.
The how bookmakers work guide goes deeper on margin, market efficiency and how bookmakers adjust prices. For finding value, read our value betting guide.