# Overround

> The overround is the amount by which a market's implied probabilities add to more than 100 per cent, which is the bookmaker's margin. Formula and meaning.

Source: https://eachwayatlas.uk/glossary/overround/
Updated: 2026-11-07

Overround is the amount by which the implied probabilities of every outcome in a market add up to more than 100 per cent, and it is the source of a bookmaker's margin. It is worked out as the sum of 1 divided by each decimal price, minus 1. The five-runner calculation is on [the bookmaker margin claim](https://eachwayatlas.uk/each-way/bookmaker-margin-claim/).

## What overround means

A fair market on every outcome would add up to exactly 100 per cent. A bookmaker's prices add up to more, and the extra is the overround.

Think of it as the built-in margin in a set of odds. The bigger the extra, the less the prices pay in total compared with the true chances.

Why it matters: you cannot read a single price as a pure chance of winning, because the margin is spread across the prices.

**The short version:** overround is the percentage above 100 per cent in a market.

## The formula, step by step

Each step uses [implied probability](https://eachwayatlas.uk/glossary/implied-probability/). Prices should be in decimal first; see [how to read odds](https://eachwayatlas.uk/each-way/how-to-read-odds/).

**Working out the overround, no figures · Editorial formula · checked 7 November 2026**

| Step | What to do |
|---|---|
| 1 | Write every price in the market as a decimal price |
| 2 | Divide 1 by each decimal price to get its implied probability |
| 3 | Add the implied probabilities of every outcome |
| 4 | Subtract 1 (or 100 per cent) from the total: the result is the overround |

We run no numbers here. The calculation on a five-horse market is on [the bookmaker margin claim](https://eachwayatlas.uk/each-way/bookmaker-margin-claim/).

**The short version:** total the implied probabilities and subtract 100 per cent.

## What it means for each-way bettors

An each-way bet adds the place part, which pays at a fraction of the win odds. That is a separate question from the margin; see [places and fractions](https://eachwayatlas.uk/each-way/places-and-fractions/).

The margin is a reason to compare terms across bookmakers rather than to assume any price is fair.

**The short version:** the margin sits in the prices, so read the odds, places and fraction together.

## What we have and have not checked

This page has no calculation of its own, to keep the working in one place. The definition source is still to be read.

**Overround facts · checked 7 November 2026**

| Fact to read | Where to read it | Status |
|---|---|---|
| A definition of margin from a regulator, organiser or operator | Gambling Commission or operator help pages, dated | Not verified |
| The formula as published by a primary source | Primary source, with the date read | Not verified |
| A market overround we have calculated | Page on the bookmaker margin claim, with the date | Not verified |

**The short version:** definition and formula are shown; sources are marked Not verified.