What is the overround?

The amount by which the implied probabilities in a market exceed 100%. If home, draw and away imply 47.6%, 29.4% and 27.8%, the book is 104.8% and the overround is 4.8%.

Is the margin the same as the bookmaker’s profit?

Only if the bookmaker takes a balanced book, which it rarely does. The margin is the edge built into the prices; the profit on a market depends on where the money went and what won.

What is a typical margin in football?

Around 2 to 3% on the match result at the sharpest bookmakers and exchanges, 5 to 8% at most high-street bookmakers, and higher again in niche markets such as correct score. Accumulators compound the margin of every leg.

How is the margin removed?

This calculator divides each implied probability by their total, which shares the margin across outcomes in proportion. Other methods (Shin, the power method) put more of it on the outsiders, which better reflects how bookmakers actually price longshots; the difference is small on short prices.

Free tool

Bookmaker margin calculator

How much of the market is margin, and what the prices would be without it.

Market

Home

Draw

Away

Margin removed proportionally (the multiplicative method). Prices in any format.

Bookmaker margin: 4.81%; the book adds to 104.8%
Home: implied → fair: 47.6% → 45.4%; fair price 2.20
Draw: implied → fair: 29.4% → 28.1%; fair price 3.56
Away: implied → fair: 27.8% → 26.5%; fair price 3.77

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Why the margin matters more than the price

Two bookmakers can quote the same favourite at the same price and still be very different bets, because one has a 3% margin spread across the market and the other has 8%. The margin is the bookmaker’s edge before anything happens on the pitch, and it is paid on every bet, win or lose.

Comparing fair prices rather than quoted prices tells you which bookmaker is actually closest to the true odds. It also tells you how much better than the market your own probability has to be before a bet is worth anything: a 5% margin means a price that looks fair is really 5% short.

How this site uses de-vigged prices

Closing line value — the measure of whether a bet beat the market — is computed against the bookmakers’ de-vigged probabilities, not the raw prices, and the calibration backtest scores the model against the same fair probabilities. Raw prices would flatter any record, because every bet would appear to beat a market that was carrying a margin.

Questions

What is the overround?: The amount by which the implied probabilities in a market exceed 100%. If home, draw and away imply 47.6%, 29.4% and 27.8%, the book is 104.8% and the overround is 4.8%.
Is the margin the same as the bookmaker’s profit?: Only if the bookmaker takes a balanced book, which it rarely does. The margin is the edge built into the prices; the profit on a market depends on where the money went and what won.
What is a typical margin in football?: Around 2 to 3% on the match result at the sharpest bookmakers and exchanges, 5 to 8% at most high-street bookmakers, and higher again in niche markets such as correct score. Accumulators compound the margin of every leg.
How is the margin removed?: This calculator divides each implied probability by their total, which shares the margin across outcomes in proportion. Other methods (Shin, the power method) put more of it on the outsiders, which better reflects how bookmakers actually price longshots; the difference is small on short prices.

The same numbers on real fixtures

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A calculator turns your numbers into other numbers. It does not know whether your numbers are right, and no arithmetic makes an outcome certain. Never stake money you cannot afford to lose.