Work out the margin on any market
Every price a bookmaker offers hides a small charge. The calculator below finds it. Choose a market type, type in the odds for each outcome as they appear on the slip, and the figures update as you go. It accepts fractional prices such as 5/2, decimal prices such as 3.50 and the word “evens”.
Check the margin on any market
Type the price of every outcome: fractional (5/2), decimal (3.50) or "evens".
- 47.6%fair 2.20
- 29.4%fair 3.56
- 27.8%fair 3.77
- Book total (overround)
- 104.8%
- Bookmaker margin
- 4.81%
- Kept from every £100 staked, on average
- £4.59
Some calculators divide the excess by the book total instead: 4.59%. Both describe the same price.
Every outcome needs odds of 1.01 or more, or a fraction such as 6/4.
The scale shows the median football match-result margin of the bookmakers we track, from our first 13 days of odds, from Betfair Sportsbook (5.90%) to BoyleSports (10.81%). Markets with more outcomes, such as races, usually carry wider margins.
How the calculator reaches its numbers
The method is the one bookmakers use themselves, run backwards. Each price becomes an implied chance: divide one by the decimal odds, so 2.10 implies 47.6% and 3.40 implies 29.4%. In a fair market every outcome’s chance would add up to exactly 100%, because one of them must happen. A bookmaker’s prices always add up to more.
That total is the overround, and the part above 100% is the margin. It is the bookmaker’s built-in edge. Over many bets, a margin of 5% keeps about £4.76 of every £100 you stake, whatever the results. The calculator shows that figure too, because it is easier to picture than a percentage.
Fair odds come from the same sum. Multiply each price by the overround and you get the odds a margin-free market would show. The gap between the price on offer and the fair price is what you give up on that outcome. The gap is not always spread evenly, so one outcome can carry more of the margin than the others.
Reading your result against UK bookmakers
A margin on its own says little until you have something to set it against. The scale under the result does that. It marks the median football match-result margin of the lowest, the typical and the highest bookmaker we track, taken from the odds we record every day across English and Scottish football.
Compare like with like. Our figures describe three-way match-result markets, so a football 1X2 you enter is a direct comparison. A two-way market such as over or under 2.5 goals can sit higher or lower, and a race with a dozen runners usually runs far wider. The calculator still works there; the scale simply becomes a rough guide.
Exchanges show a different picture again. Their prices are set by other punters, so the book on an exchange often sums to close to 100%. You pay commission on net winnings instead, which our bookmaker margins tables already include. To compare a bookmaker with an exchange fairly, look at those tables rather than the raw exchange price.
When it is worth checking a margin
Run a market through the calculator before a bet you would place often: a weekly acca, a regular stake on one league, or the same type of market every Saturday. A gap of two or three points between two bookmakers adds up quickly over a season, as our free bets page shows with a worked example.
It also helps to check a price that looks generous. A boosted price or a headline offer can sit inside a market whose other prices have been cut to pay for it. Enter the whole market and the total gives that away at once. For the theory behind all of this, our guide to how bookmakers set odds walks through each step with round numbers.
A low margin is a better price, never a route to profit. Every bet still wins or loses on its own, and the bookmaker’s edge only shrinks; it never disappears. Set a budget before you bet, and use the deposit limits and time-outs every licensed bookmaker offers. Our safer gambling page lists the free support available.
Frequently asked questions
How do you calculate a bookmaker's margin?
Turn every price in the market into an implied chance by dividing one by the decimal odds. Add those chances together. The amount above 100% is the margin. Three prices of 2.10, 3.40 and 3.60 add up to 104.8%, so the bookmaker has built in a margin of 4.8%.
What is a good betting margin on football?
It depends on the market. On a football match result the bookmakers we track differ by several percentage points, and the exchanges usually sit below all of them once commission is counted. Our bookmaker margins page shows the current median for every site we track, refreshed weekly.
What is the difference between margin and overround?
They describe the same thing from two sides. The overround is the total of the implied chances, such as 104.8%. The margin is the part above 100%, here 4.8%. Some writers divide that excess by the total instead and report a slightly smaller figure, which the calculator also shows.
Can I use the calculator for horse racing?
Yes. Add an outcome for every runner and enter each price. Races and outrights usually carry much wider margins than a two-way or three-way football market, because the bookmaker spreads its edge across many runners, so expect a far higher figure than on a match result.
What are fair odds?
Fair odds are the prices a market would show with the margin taken out, so the implied chances add up to exactly 100%. The calculator scales every price by the overround. A fair price tells you roughly what an outcome is worth and how much the bookmaker has shaved off it.
Why can the total come out below 100%?
Only when the prices come from different bookmakers, or when a price has moved since you noted it. Each single book is priced above 100%. Combining the best price for each outcome from several sites can push the total below 100%, which bookmakers close quickly.