# Bookmaker margin: does it make long-run winning almost impossible?

> Checks whether the bookmaker margin makes long-run winning almost impossible: how margin is calculated, worked examples, multi-bet effect and what we have not confirmed.

Source: https://bookiechecklist.com/are-bookmaker-odds-fair/
Updated: 2026-11-13

"The margin makes long-run winning almost impossible" is half confirmed. The arithmetic shows that a margin cuts the average return: a market priced at 1.91 on both sides carries 4.71%. The word "impossible" is not confirmed, because no primary source we have read measures customers' long-run results. Two sources are still to be logged.

## How margin is calculated

For each outcome, the implied probability is 1 divided by the decimal price. Add them across the market. A fair book adds to 100%. Anything above is the margin, also called the overround.

This is a definition, not a claim about any one operator. Our term pages cover [implied probability](https://bookiechecklist.com/implied-probability/) and [margin and overround](https://bookiechecklist.com/bookmaker-margin-overround/).

## Worked examples

Illustrative examples, not prices. Each row shows prices we chose to show the method.

**Margin from three illustrative markets · source: our own arithmetic · checked 2026-11-13**

| Market | Decimal prices | Sum of implied probabilities | Margin |
|---|---|---|---|
| Two outcomes | 1.91 and 1.91 | 104.71% | 4.71% |
| Three outcomes | 2.60, 3.40 and 2.90 | 102.36% | 2.36% |
| Four-leg multi, 5% on each leg | Fair price divided by 1.05 per leg | 121.55% | Average return A$82.27 per A$100 |

At 1.91 a bettor needs to win 52.36% of bets to break even. A customer who thinks the chance is 50% faces an expected value of A$100 × (0.50 × 1.91 − 1) = −A$4.50 per A$100 staked.

**Short answer:** the margin lowers the average return and compounds across legs; that winning is almost impossible is not confirmed.

## What operators and exchanges publish

Our plan records two kinds of published rules: how best odds guaranteed (BOG) works, and how a betting exchange charges commission. We have not read either yet, so we state no figure. See [best odds guaranteed](https://bookiechecklist.com/best-odds-guaranteed-bog/).

We also have two primary sources to read on how odds are built, from a regulator or a help service. Until they are logged, we describe the formula only.

## When this is wrong

The page is wrong if a market is priced below 100% in total, which would show a negative margin. It would also be wrong if a primary source shows customers profiting at a stated rate.

The formulas are re-checked once a year. Your own markets can be run through the [expected value calculator](https://bookiechecklist.com/ev-calculator/).

## Check it yourself

1. Write down every price in a market.
2. Divide 1 by each price and add the results.
3. Subtract 1. The result is the margin.

For a multi, see [what is a multi bet](https://bookiechecklist.com/what-is-a-multi-bet/) and [how to read decimal odds](https://bookiechecklist.com/how-to-read-decimal-odds/).

## How the margin grows across legs

A multi bet applies the margin once per leg. The effect compounds, because each price is multiplied by the next.

Illustrative example, not a price. Assume each leg carries a 5% margin, so each price is the fair price divided by 1.05. Average return per A$100 staked then falls as legs are added:

- 2 legs: A$90.70, from 1 / 1.05 squared;
- 4 legs: A$82.27;
- 6 legs: A$74.62.

The larger payout on a longer multi is therefore paid for with a lower average return. One lost leg still loses the whole bet.

This is arithmetic on an assumed margin. We have not read an operator's margin on any real multi.

## 18+ and where to get help

18+ only. Gambling can be harmful. Need help? Call Gambling Help Online on 1800 858 858 (free, 24/7) or visit gamblinghelponline.org.au. To exclude yourself from licensed Australian online and phone wagering providers, register with BetStop at betstop.gov.au.

## FAQ

**How do you calculate the bookmaker margin?**

Add the implied probabilities of every outcome in a market (1 divided by each decimal price), then subtract 1. A total of 104.71% is a margin of 4.71%.

**Does a margin make winning impossible?**

Not confirmed. Arithmetic shows a margin lowers the average return. It does not prove that no customer can profit, and no primary source we have read measures that.

**Does the margin grow on a multi bet?**

Yes, because it applies to each leg. In the illustrative example below, four legs each carrying a 5% margin return on average A$82.27 per A$100 staked.

**Do operators publish their margins?**

Not confirmed on 13 November 2026. We have not found an operator page that states a margin, so we calculate it from published prices and label it as a calculation.