By Michael ·
Betting odds tell you how much a winning bet pays and how likely the bookmaker thinks the outcome is. In the UK you'll see them as fractions (5/2) or decimals (3.50), and both describe the same price.
Fractional odds
Fractional odds are the traditional UK format. The first number is what you win, and the second is what you stake.
At 5/2 ("five to two"), you stake £2 to win £5. A £10 bet wins £25, and you get your £10 back too, so £35 in total. At 1/1, called evens, you win the same as you stake: £10 wins £10. At 1/2 ("two to one on"), you stake £2 to win £1. That's odds-on, where you win less than you stake.
When the first number is bigger than the second, the price is odds-against. When it's smaller, it's odds-on. Odds-on means the bookmaker thinks the outcome is more likely to happen than not.
Some fractions look odd at first: 11/10, 5/6, 100/30, 13/8. They're points on the same scale. 100/30 is the same as 10/3, a little more than 3/1.
Decimal odds
Decimal odds show the total you get back for every £1 staked, including the stake. At 3.50, a £10 bet returns £35, which is £25 in winnings plus your £10 stake. At 2.00, which is evens, £10 returns £20. At 1.50, which is odds-on, £10 returns £15.
To find the winnings alone, take 1 off the decimal odds and multiply by your stake. At 2.10, a £10 bet returns £21.00, so you win £11.00.
Betting exchanges show decimal odds. An exchange is a site where you bet against other people instead of a bookmaker. If you're doing matched betting and your bookmaker account lets you switch to decimal, switch it. Working out whether 11/8 is longer than 2.40 in your head is how mistakes happen.
Converting between the two
To turn a fraction into a decimal, divide the top by the bottom, then add 1. So 5/2 = 2.5, plus 1 = 3.50. To go the other way, take away 1 and turn what's left into a fraction: 3.50 - 1 = 2.5 = 5/2.
Prices you'll see every week:
Fractional | Decimal | Implied chance |
|---|---|---|
1/2 | 1.50 | 66.7% |
5/6 | 1.83 | 54.5% |
Evens (1/1) | 2.00 | 50.0% |
11/10 | 2.10 | 47.6% |
6/4 | 2.50 | 40.0% |
5/2 | 3.50 | 28.6% |
100/30 | 4.33 | 23.1% |
9/1 | 10.00 | 10.0% |
Some fractions don't convert to a neat decimal. 5/6 is 1.8333..., usually shown as 1.83. Rounding like that rarely matters, but it's why a bookmaker's fractional price and an exchange's decimal price can look a little apart when they're the same.
What odds say about probability
Every price has an implied probability: the chance of the outcome that the price suggests. To work it out, divide 1 by the decimal odds. At 2.00, that's 1 ÷ 2 = 50%. At 10.00, it's 10%. At 1.50, it's 66.7%.
It's what the price implies, not a fact. The bookmaker's opinion, the money bet and the margin all feed into it. A horse at 10.00 doesn't win exactly one race in ten.
The bookmaker's margin
Add up the implied chances for every outcome in a bookmaker's market and you'll get more than 100%. The extra is the bookmaker's margin, sometimes called the overround.
Example: a made-up match prices the home side at 2.10, the draw at 3.40 and the away side at 3.60. The implied chances are 47.6% (1 ÷ 2.10), 29.4% (1 ÷ 3.40) and 27.8% (1 ÷ 3.60). Together that's 104.8%.
That 4.8% is roughly the bookmaker's built-in edge on that market. On an exchange, the top back prices for the same match might be 2.20, 3.60 and 3.85, which add up to 99.2%. Exchanges such as Betfair, Smarkets and Matchbook don't build a margin into the price. They charge commission on your net winnings on a market instead. Our guide to betting exchanges explains how that works.
Bookmaker prices are usually a bit shorter than exchange lay prices, so covering a back bet costs a little. That cost is the qualifying loss. When a bookmaker price is longer than the lay price, that's an arb, covered in arbitrage vs matched betting.
Odds in matched betting
In matched betting you compare two prices for the same outcome. The back price is the bookmaker's price for it to happen. The lay price is the exchange's price for betting that it won't. The closer they are, the cheaper it is to cover your bet.
Example: a bookmaker offers 2.10 and the exchange lay is 2.14, with 2% commission. To cover a £10 back bet you lay £9.91. Your liability, what you pay out if the lay loses, is £11.29. The qualifying loss is £0.29 whatever the result, and the match rating is 97.08%.
The rating compares the back price with the lay price, after commission. At 100% there'd be no loss at all. Our lay betting guide shows where those figures come from. The 2UP Calculator is a free page that needs no account, and it works out the lay stake and liability for any pair of prices.
Each-way odds: the place part
An each-way bet is two bets: one on the horse to win, and one on it to finish in the places. The place part pays a fraction of the win odds, and the race's each-way terms set the fraction.
The fraction applies to the winnings, not to the decimal price. Example: a horse at 9.00 (8/1) with 1/5 odds a place. The win part pays 8 to 1, so the place part pays 8 ÷ 5 = 1.6 to 1, and the place odds are 2.60. At 1/4, the same horse's place odds are 3.00.
A common mistake is to divide the decimal price itself (9.00 ÷ 5 = 1.80), which is wrong. The Extra Place Calculator, another free page, does this sum for you. Our guide to how many places each way covers which races pay which terms.
Why odds move
Prices aren't fixed. A bookmaker moves its odds when money comes in, when team news breaks, or when a rival changes its price. On an exchange, the price moves as people place and cancel bets.
For most punters that's background noise. For a matched bettor it matters, because you rely on two prices staying close for the minute it takes to place both bets. If the lay price drifts from 2.14 to 2.30 between your back and your lay, the qualifying loss in the example above goes from 29p to 97p.
Check both prices again right before you place anything, and recalculate with the prices you actually got.
What goes wrong with odds
The first mistake is typing a fraction as a decimal, because 5/2 isn't 5.2. Example: you back £10 at 5/2 (3.50) and lay at 3.60 with 2% commission, but you type 5.2 into a calculator. It tells you to lay £14.53 instead of £9.78. If the selection wins, you're down £12.77. If it loses, you're up £4.23. You've turned a 42p qualifying loss into a bet on the result.
The second is misreading odds-on prices. 1/2 is 1.50, not 0.50 or 2.00. A decimal price includes your stake, so it's above 1 for any price.
The third is wrong place odds: dividing the decimal price instead of the winnings, or using 1/4 when the race pays 1/5. The last is forgetting the price moved. The price you saw a minute ago isn't always the price you got, so check the bet slip once the bet is placed.
Questions people ask
How do I work out my winnings?
With decimal odds, multiply your stake by the odds for the total return, then take off the stake. £10 at 3.50 returns £35, which is £25 more than you staked.
Are decimal or fractional odds better?
They're the same price written two ways. Decimals are simpler to compare, and they're what exchanges and calculators use. Our football betting terms glossary explains the other words you'll meet on a bet slip.
Try it with real prices
Pick a price you've seen today and convert it. Then put it into the 2UP Calculator next to an exchange lay price. Watching the lay stake and liability change as the prices move is a good way to make odds feel normal.
Checked against Betfair's, Smarkets' and Matchbook's terms on 14 November 2026.
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