What is bookmaker margin?

It is the amount by which a market's implied probabilities exceed 100%. That excess is the bookmaker's built-in edge, charged on every bet regardless of the result.

What is the difference between overround and margin?

Overround is the raw excess: total implied probability minus 100%. Margin expresses that excess as a share of the whole book, so a 104.7% market has 4.7% overround and 4.49% margin.

What is a good margin?

Under 3% is sharp, 3–6% is typical for major football and US sports markets, and anything above 8% is expensive. Niche markets and long-odds specials often exceed 15%.

Are vig, juice and margin the same thing?

Effectively yes. Vig or juice is the American term for the same built-in commission that UK and European bettors call the overround or margin.

How do I use fair odds?

Fair odds show what the price would be with the margin removed. Comparing a bookmaker's price to the fair odds of a sharper market is a rough way to judge whether a price is competitive.

Bookmaker Margin Calculator

Add every outcome in a market and this calculator totals their implied probabilities. Any amount above 100% is the bookmaker's margin — the edge charged on the market — and the table shows what each price would be without it.

Odds format

Outcome 1
Outcome 2
Outcome 3

Total implied probability

104.81%

A fair book totals exactly 100%.

Bookmaker margin

4.59%

Overround 4.81%

Fair odds for each outcome once the margin is removed
Outcome	Implied	Fair chance	Fair odds
Outcome 1	47.62%	45.43%	2.20
Outcome 2	29.41%	28.06%	3.56
Outcome 3	27.78%	26.50%	3.77

The formulas

total = Σ (1 ÷ decimal oddsᵢ)

overround% = (total − 1) × 100

margin% = (total − 1) ÷ total × 100

fair probabilityᵢ = (1 ÷ oddsᵢ) ÷ total

fair oddsᵢ = 1 ÷ fair probabilityᵢ

This normalises the margin proportionally across outcomes. Real books load more margin onto long shots, so fair odds on outsiders are an approximation.

Worked example

A football match is priced 2.10 / 3.40 / 3.60. The implied probabilities are 47.62%, 29.41% and 27.78%, totalling 104.81%. The overround is 4.81% and the margin is 4.59%. Removing it proportionally gives fair prices of about 2.20, 3.56 and 3.77.

Typical margins by market type.
Market	Typical total	Margin
Major football 1X2	104–107%	3.8–6.5%
NFL point spread (−110 both sides)	104.8%	4.5%
Tennis match winner	103–106%	2.9–5.7%
Outright tournament winner	115–140%	13–29%
Player props and specials	108–125%	7.4–20%

Common mistakes

Leaving out an outcome. Forgetting the draw in a 1X2 market makes the margin look far smaller than it is.
Comparing markets with different outcome counts. A 3-way market naturally totals higher than a 2-way one at the same per-outcome margin.
Assuming fair odds are true odds. They are margin-free prices derived from the bookmaker's numbers, not an independent estimate of what will happen.

Frequently asked questions

Last reviewed: 24 August 2026. Formulas on this page are checked against the unit test suite that powers every bet.ing calculator.