How do you calculate bookmaker margin?

Sum the implied probabilities (1 ÷ decimal odds) of all outcomes. Overround % = total − 100. Example: Home 2.10, Draw 3.40, Away 3.60 → 47.6% + 29.4% + 27.8% = 104.8%. Margin = 4.8%.

What is a fair odds price?

Fair odds remove the bookmaker margin by normalising each implied probability. Fair probability = implied probability ÷ total overround. Fair odds = 1 ÷ fair probability. This is the "true" price with zero margin built in.

What margin is acceptable?

Under 3% is excellent (Pinnacle on major markets, Betfair Exchange). 3–6% is average for mainstream books on main markets. Above 8% is poor and found on player props, live betting, and outright markets at soft bookmakers.

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Margin Calculator

Enter the decimal odds for each outcome in any market to see the bookmaker overround, margin, and the fair no-vig price for every selection.

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What Is Bookmaker Margin?

The margin (or overround) is the built-in profit layer in every bookmaker market. It ensures the book makes money regardless of the outcome by inflating the sum of implied probabilities above 100%. The difference between the quoted implied probability and the true probability is what you pay to place a bet.

For a detailed explanation with worked examples, see our bookmaker margin guide.