Overround and Margin Calculator
Enter the odds for every outcome in one market. You get the overround, the payout rate and the fair chance and fair odds of each outcome.
Betting is for adults aged 18 or over, and you can lose money. This page explains the maths and does not encourage betting. If gambling is a problem for you or someone close to you, contact BeGambleAware or GamCare (National Gambling Helpline 0808 8020 133).
Worked examples
A two way market
1.91 and 1.91
Book 104.7%, overround 4.7%, payout 95.5%
Fair chance 50% each and fair odds 2.00.
A football match result market
2.10, 3.40 and 3.60
Book 104.8%, overround 4.8%
Fair chances are about 45.4%, 28.1% and 26.5%.
About Overround and Margin Calculator
A bookmaker's odds, turned into chances, add up to more than 100%. The excess is called the overround, and it is where the bookmaker's profit margin comes from. In a two way market priced at 1.91 on each side, the chances add up to 104.7%, so the overround is 4.7%. This calculator takes the odds for every outcome in a market and shows the overround, the payout rate and the margin.
It also removes the margin to show fair chances and fair odds, by scaling each implied chance down in proportion so that they add up to exactly 100%. That is the simplest method, and a useful way to compare prices between bookmakers or to see what a market really thinks. This page explains the maths and does not encourage betting.
How to use Overround and Margin Calculator
- List every possible outcome of the market, one per line, with its odds. A name before the odds is optional.
- Use fractional, decimal or American odds, mixed if you like.
- Read the book percentage, the overround and the payout rate.
- Look at the fair chance and fair odds for each outcome.
Common uses
- Comparing the margin on a football match result between two bookmakers
- Finding the fair odds behind a market
- Spotting a market with an unusually high margin
- Learning how bookmakers make money
Frequently asked questions
What is the overround?
It is the sum of the chances implied by the odds in a market, minus 100%. A market whose chances add up to 104.7% has an overround of 4.7%.
What is the payout rate?
The reverse of the book percentage: 100% divided by the book. If the book is 104.7% the payout rate is 95.5%, so on average about £95.50 in every £100 wagered is returned.
How are fair odds worked out?
Each implied chance is divided by the book total, so the chances add up to 100%, and the fair odds are 1 divided by the fair chance. Other methods share the margin differently.
What overround is the 2.10, 3.40, 3.60 market?
The implied chances are 47.6%, 29.4% and 27.8%. They add up to 104.8%, an overround of about 4.8%.
Why must I list every outcome?
The overround is only meaningful for a complete market. If an outcome is left out, the total will be too low and the margin looks smaller than it is.