The bookmaker margin is the built-in edge a bookmaker adds to its odds so that, across all outcomes, it expects to make a profit whatever the result. You can calculate it by converting each price in a market to an implied probability and adding them up: anything over 100% is the margin. Knowing how to work this out helps you spot which bookmakers offer fairer odds and where to look for value.
What is bookmaker margin?
If a bookmaker priced a coin toss fairly, it would offer 2.00 on heads and 2.00 on tails. Over thousands of bets it would pay out exactly what it took in. To make money, it instead offers something like 1.91 on each side. The gap between the fair price and the offered price is the margin.
You will see several names for the same idea:
- Margin is the general term used in Europe and Africa.
- Overround describes the total implied probability above 100%, for example a "105% book".
- Vig or vigorish (sometimes "juice") is the American term. The classic US price of −110 on both sides of a spread carries a vig of around 4.5%.
- Hold is the share of total stakes the bookmaker expects to keep.
How to calculate bookmaker margin
The method works for any market where the outcomes cover every possibility, such as 1X2, over/under or both teams to score.
- Convert each decimal price to implied probability: 1 ÷ odds.
- Add the implied probabilities together. This total is the overround.
- Subtract 100%. The result is the margin expressed as overround.
If your odds are fractional or American, convert them to decimal first with our odds converter, or see betting odds explained.
Worked example: a 1X2 football market
Suppose a Premier League match is priced like this:
| Outcome | Decimal odds | Implied probability |
|---|---|---|
| Home | 2.10 | 1 ÷ 2.10 = 47.62% |
| Draw | 3.40 | 1 ÷ 3.40 = 29.41% |
| Away | 3.60 | 1 ÷ 3.60 = 27.78% |
| Total | 104.81% |
The book adds up to 104.81%, so the overround is 4.81%.
There is a second, closely related way to express this: the share of stakes the bookmaker expects to keep if money is spread in proportion to the odds. That figure is 1 − (1 ÷ 1.0481), which is about 4.59%. Both numbers describe the same market; just be consistent when comparing bookmakers. Our margin calculator shows both.
Working out the fair odds
You can strip the margin out to estimate the "fair" odds. Divide each implied probability by the total overround, then convert back to odds:
- Home: 47.62% ÷ 1.0481 = 45.43%, fair odds about 2.20
- Draw: 29.41% ÷ 1.0481 = 28.06%, fair odds about 3.56
- Away: 27.78% ÷ 1.0481 = 26.50%, fair odds about 3.77
This simple proportional method assumes the margin is spread evenly, which is not always true. Many bookmakers load more margin onto longshots than favourites, so treat the result as an estimate rather than a precise truth.
Two-way markets
For a two-way market the maths is even quicker. Over 2.5 goals at 1.90 and under 2.5 at 1.90 gives 52.63% + 52.63% = 105.26%, an overround of 5.26%. Compare a bookmaker offering 1.95 on both sides: 51.28% × 2 = 102.56%, an overround of just 2.56%. The second bookmaker is giving you meaningfully better odds on the same market.
Why the margin matters
The margin is effectively the price you pay to bet. A lower margin means more of every winning bet goes to you.
Imagine you place 200 bets of R100 each at fair odds. In theory, your long-run expectation is roughly break-even. Add a 5% margin and you would expect to lose around R1,000 over those R20,000 of stakes; add 10% and it rises to around R2,000. Real results vary enormously from this simple average, but the direction is clear: a higher margin works against you every time you bet.
Margins vary widely depending on:
- The bookmaker. Some operators run lean books on major markets; others take more.
- The sport and league. Top football leagues and major US sports are usually priced more tightly than lower leagues or niche sports.
- The market type. Main markets such as 1X2 and totals usually carry lower margins than exotic props, correct scores or player specials.
- Accumulators. Margins compound across every leg. If each of four legs carries a 5% overround, the combined slip carries roughly 1.05 × 1.05 × 1.05 × 1.05 ≈ 1.216, or about 21.6%. Our accumulator betting guide explores this.
How to use margins to find better odds
Compare prices across bookmakers
The most practical way to beat high margins is line shopping, choosing the best price for each selection from several bookmakers. Even if every bookmaker has a 5% margin overall, they rarely agree on each individual price. One might be generous on the home win while another is generous on the draw.
Our odds comparison pages show prices from multiple bookmakers side by side, and we also calculate the margin on each market. Taking the best price for each outcome often produces a combined book much closer to 100% than any single bookmaker offers, which shows how much shopping around can help.
Prefer low-margin markets
If you regularly bet on the same type of market, check which bookmakers price it tightly. Our bookmaker reviews and methodology page explain how we assess pricing.
Be careful with boosts and specials
A boosted price can look attractive, but compare it against what other bookmakers offer for the same outcome. Sometimes the "boost" only brings the price back to where the market already is.
Margin and value are not the same
A low margin means a bookmaker is pricing fairly overall, but it does not tell you whether a particular bet is good value. Value depends on whether the odds are higher than the real chance of the outcome. Understanding margin is the first step; our guide on how to find value bets covers the next.
No margin calculation or comparison guarantees a profit. Betting always carries risk, so set limits and only stake money you can afford to lose. Our responsible gambling page has help and tools. You must be 18 or over to bet (21+ in most US states and 25 in Uganda).
FAQ
What is a good bookmaker margin?
There is no single figure, because margins depend on the sport and market. As a rule of thumb, a lower overround is better for you, and main markets in top leagues usually carry the lowest margins. Compare the same market across several bookmakers to see who is most competitive.
What is the difference between overround and margin?
Overround is the total implied probability of a market above 100%, such as 104.81%. Margin is the general term for the bookmaker's edge and is often quoted either as that excess (4.81%) or as the share of stakes the bookmaker expects to keep (about 4.59%). Both point the same way.
How do I calculate vig on American odds?
Convert the American odds to decimal or implied probability first. For −110 on both sides, each side is 52.38% implied, totalling 104.76%. That is a 4.76% overround, or about 4.5% expressed as the bookmaker's expected hold.
Can a market have a margin below zero?
A single bookmaker's market almost never does. However, if you take the best price for each outcome from different bookmakers, the combined overround can sometimes drop close to or even below 100%. That is why comparing odds across bookmakers is so useful.
Do betting exchanges have a margin?
Exchanges work differently. Prices are set by other users, so the back and lay odds are often close to fair, but the exchange charges a commission on net winnings instead. Factor in that commission when comparing exchange prices with bookmaker odds.