Bookmaker Margin Explained: How Overround Is Built Into Every Market
Every betting market carries a margin. Learn to calculate it in seconds and you will never look at a price the same way again.
Table of contents
Quick answer
The bookmaker margin is the built-in edge in a market. Add up 1 ÷ odds for every outcome: anything above 100% is the overround. A football market priced 2.10 / 3.40 / 3.60 totals 104.8%, a margin of about 4.6%.
The overround in one example
Take a football match priced Home 2.10 · Draw 3.40 · Away 3.60.
| Outcome | Odds | Implied probability |
|---|---|---|
| Home | 2.10 | 47.6% |
| Draw | 3.40 | 29.4% |
| Away | 3.60 | 27.8% |
| Total | — | 104.8% |
The book totals 104.8%, an overround of 4.8%. Expressed as the share of all stakes the bookmaker expects to keep, the margin is 1 − 1 ÷ 1.048 ≈ 4.6%.
Why it matters
The margin is the cost of betting. On a market with a 5% margin, a bettor with no edge loses about 5% of their stakes over time. On a 10% margin, they lose about twice as fast.
Fair odds
Remove the margin and you get approximate “fair” odds. Divide each implied probability by the book total: 47.6% ÷ 1.048 = 45.4%, or fair odds of about 2.20 for the home win.
Margins and accumulators
Each leg of an accumulator carries its own margin, and they compound. That is one reason long accumulators are so profitable for bookmakers — see our accumulator guide.
Overround / Margin Calculator
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Frequently asked questions
What is a typical margin?
It varies widely by sport, market and bookmaker. Major markets tend to be tighter; niche and in-play markets wider.
Can I avoid the margin?
No, but you can reduce it by comparing prices and favouring lower-margin markets.
Sources & references
- UK Gambling Commission www.gamblingcommission.gov.uk
- BeGambleAware www.begambleaware.org
We check every figure against the source listed. Spotted an error? Request a correction.
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