How Bookmakers Make Money: Margin, Not Balanced Books
A bookmaker's margin is the surplus built into its odds: the sum of 1/odds over every outcome of one market is above 1, and whatever is above 1 is the bookmaker's cut. Odds of 1.98 / 3.55 / 3.58 add up to 1.0661, a 6.61% margin. Bookmakers earn not by predicting results better than you, but because every price pays a little less than the real chances justify. This guide shows the formula, why the popular "balanced book" story is mostly a myth, and what margins look like across markets.
Key takeaways
- The margin is the sum of 1/odds over one market minus 1: odds of 1.98 / 3.55 / 3.58 carry a 6.61% margin.
- Bookmakers do not need balanced books because their prices are accurate: favourites priced at 70–80% won 75.5% of 6,351 matches.
- A lopsided book on one match risked a loss of 38,600 on 100,000 staked, yet its expected profit was 6.4%, almost the same as a balanced one.
- On a five-leg accumulator with a 5% margin on each leg, the combined margin is 27.6%.
- Surebets exist because bookmakers set prices separately: the best prices of several firms can add up to less than 1.
How to calculate a bookmaker's margin
Odds are the inverse of probability: 2.00 means 50%, 4.00 means 25%. If a bookmaker priced a match fairly, the probabilities of all outcomes would add up to exactly 100%. In practice the sum is always higher.
margin = 1/odds₁ + 1/odds₂ + 1/odds₃ − 1
For two-way markets (over/under, Asian handicap, tennis) you add two terms, for 1X2 three. Always use one bookmaker's prices on one market. Mixing the best prices of several bookmakers gives a market nobody offered, and when that sum drops below 1 you have a surebet: see what is arbitrage betting.
A worked example
For Legia – Wisła Kraków (Polish Ekstraklasa, 11 October 2026) our model gave: home win 47.2%, draw 26.6%, away win 26.3%. The fair odds, without any margin, are the inverses: 2.12 / 3.76 / 3.80. Now picture a bookmaker offering 1.98 / 3.55 / 3.58:
| Outcome | Chance (model) | Fair odds | Bookmaker odds | 1/bookmaker odds |
|---|---|---|---|---|
| Home | 47.2% | 2.12 | 1.98 | 50.51% |
| Draw | 26.6% | 3.76 | 3.55 | 28.17% |
| Away | 26.3% | 3.80 | 3.58 | 27.93% |
| Sum | 100.1%* | 106.61% |
* The chances add up to 100.1% because of rounding.
- Add the inverses of the bookmaker's odds: 0.5051 + 0.2817 + 0.2793 = 1.0661.
- Subtract 1: the margin is 6.61%.
- Compare with the fair price: 2.12 / 1.98 = 1.071, so the fair home price is 7.1% higher than the bookmaker's.
- Expected value at the model's chances: a home bet at 1.98 loses 6.5% of the stake on average (0.472 × 1.98 − 1 = −0.065).
Two numbers are easy to confuse. The 6.61% margin is the surplus over 100%. If bettors split their money exactly in proportion to the inverses of the odds, the bookmaker would keep 1 − 1 / 1.0661 = 6.2% of all stakes. Both describe the same thing; the second says how much really stays with the bookmaker.
The balanced book myth
The popular explanation says a bookmaker sets odds so that the same money comes in on every outcome and it wins whatever happens. In practice that rarely holds.
Take the same match and 100,000 staked at 1.98 / 3.55 / 3.58, but the way fans bet: 70% on the home side, 15% each on the draw and the away side.
| Result | Bookmaker pays out | Bookmaker's result |
|---|---|---|
| Home win | 138,600 | −38,600 |
| Draw | 53,250 | +46,750 |
| Away win | 53,700 | +46,300 |
The book is badly unbalanced, and a home win costs the bookmaker money. Its expected result at 47.2% / 26.6% / 26.3% is still +6,387, or 6.4% of turnover. A perfectly balanced book (47,375 / 26,423 / 26,202) would earn 6,198 on any result. The difference in expected profit is small; only the swings grow.
So a bookmaker needs accurate prices and a margin, not equal money on every outcome. And prices are accurate. In our database of 104 thousand matches from 37 leagues (2015–2026), with closing odds cleared of the margin:
| Favourite's chance per the market | Matches | Favourite won | Average chance from odds |
|---|---|---|---|
| 40–50% | 38,029 | 44.8% | 44.6% |
| 50–60% | 23,712 | 54.5% | 54.6% |
| 60–70% | 13,339 | 64.7% | 64.4% |
| 70–80% | 6,351 | 75.5% | 74.2% |
The gaps are fractions of a percentage point. That is why real value is rare, as we show in value betting vs arbitrage betting, and why a bettor who backs outcomes "on feel" pays the margin on average.
Margins by market
| Market | Typical margin (indicative) |
|---|---|
| 1X2 in top leagues | 3–6% |
| 1X2 in lower leagues | 6–10% |
| Over/under 2.5, main Asian handicap line | 3–7% |
| Both teams to score | 5–8% |
| Correct score | 15–30% |
| Goalscorer | 20–40% |
| Outrights (league winner, top scorer) | 15–40% |
These are ranges for the worldwide market; they vary between bookmakers and over time. You can always check them yourself by adding up the inverses of a full market.
Accumulators multiply the margin
On an accumulator the odds multiply, and so do the margins. With a 5% margin on each leg:
| Legs | Combined margin (1.05ⁿ) | Value left of 100 staked |
|---|---|---|
| 1 | 1.050 | 95.2 |
| 2 | 1.103 | 90.7 |
| 3 | 1.158 | 86.4 |
| 5 | 1.276 | 78.4 |
| 10 | 1.629 | 61.4 |
On five legs you give away 21.6% of the stake on average, on ten 38.6%.
Sharp and soft bookmakers
The industry talks about two business models:
- Sharp: a low margin (on top-league 1X2 often 2–3%), high limits, fast automatic price changes. They make money on turnover and treat winning bettors as information: their bets move the price. Pinnacle is the best-known example, and its closing odds serve as the market's benchmark.
- Soft: higher margins, slower updates, many promotions and accumulators. They make money on recreational bettors and limit those who keep beating the market, usually by cutting the maximum stake.
That difference explains why surebets exist and why arbers get limited. A soft bookmaker that lags behind a sharp price leaves a gap for a few minutes; a bettor who keeps taking those gaps is a pure cost to it. More in bookmaker limits.
How to pay less margin
- Compare prices. 2.05 instead of 1.98 on the same bet is a 3.5% higher payout. For a regular bettor that is more than the whole edge most analysis looks for.
- Bet main markets. 1X2, goals and handicaps in popular leagues carry the lowest margins.
- Keep accumulators short. Every extra leg adds another 5% or more.
- Do the math yourself. Add up the inverses of the odds. If the sum is above 1.08 on a popular league's 1X2, look elsewhere.
Arbitrage takes price comparison to its end: it backs every outcome at the best price on the market. The surebet calculator shows the result of every scenario for any combination you enter, so you can see at once whether it is a surebet.
Summary
The margin is the sum of 1/odds over one market minus 1. Bookmakers do not need balanced books; accurate prices and a margin are enough, and our calibration on 104 thousand matches shows closing odds are very accurate. Main markets carry a few percent of margin, correct scores and goalscorers far more, and accumulators multiply it. Surebets live in the gaps between bookmakers that set prices separately.
FAQ
How do you calculate a bookmaker's margin?
Add the inverses of the odds for every outcome of one market at one bookmaker and subtract 1. For odds of 1.98 / 3.55 / 3.58 that is 0.5051 + 0.2817 + 0.2793 − 1 = 0.0661, a 6.61% margin.
How do bookmakers make money if they sometimes lose a match?
They earn on the margin and on accurate pricing, not on every match. A single result can cost them a lot, but over thousands of matches their profit approaches the margin. They do not need equal money on every outcome.
What is a low or a high margin?
On top-league 1X2, up to about 4% is low, 5–6% average and above 8% high. Markets with many outcomes, such as correct score or goalscorer, normally carry 20–30%. These are indicative values, so it pays to calculate the margin yourself.
Why does an accumulator have a bigger margin than a single bet?
Because the odds of the legs multiply, and so do their margins. Five legs with a 5% margin each give 1.05⁵ = 1.276, a 27.6% margin on the slip.
What is the difference between a sharp and a soft bookmaker?
A sharp bookmaker has a low margin and high limits and changes prices quickly, earning on turnover. A soft bookmaker has higher margins and many promotions, earns on recreational bettors and limits accounts that keep winning.