Fractions, decimals and margins
LadBet Odds
Reading 17/10 and 2.70 as the same number, working out a return before you stake, and understanding why a price moves. None of it requires more than arithmetic you already have.
Odds do two things at once. They tell you what a bet pays and they tell you what the bookmaker thinks the chance is, and separating those two readings is the most useful skill anybody betting can pick up. This page does that in plain arithmetic rather than in theory.
The two formats
British betting grew up on fractions and most of the rest of the world uses decimals. Both are on the site and you can switch between them in settings; they describe exactly the same thing.
Fractional
Winnings first, stake second. At 5/2 you win five for every two staked, plus your stake back, so a £10 bet returns £35. At 1/1, called evens, you win the same as you staked. Anything where the first number is smaller is odds-on: at 4/6, a £6 stake wins £4.
Decimal
Total return per unit staked, stake included. 3.50 means a £10 bet returns £35. The conversion is one line: divide the fraction and add one. 5/2 is 2.5 plus 1, which is 3.50. Decimals are easier for multiples, because you just multiply the numbers together.
| Fractional | Decimal | £10 returns | Implied chance |
|---|---|---|---|
| 4/6 | 1.67 | £16.70 | 60% |
| 1/1 | 2.00 | £20.00 | 50% |
| 6/4 | 2.50 | £25.00 | 40% |
| 5/2 | 3.50 | £35.00 | 29% |
| 10/1 | 11.00 | £110.00 | 9% |
What a price says about probability
Divide one by the decimal price and you get the chance the price implies. 2.00 gives 0.5, which is fifty per cent. 4.00 gives 25 per cent. That number is the single most useful thing on a coupon and hardly anybody calculates it.
Why it is not the real probability
Because it includes the bookmaker’s margin. Add up the implied chances across every outcome in a market and the total comes to more than a hundred per cent; the excess is the margin. A two-way market where both sides are 10/11 implies 52.4 per cent each, totalling 104.8, so the margin is 4.8 per cent.
Using it to compare markets
A thinner margin means more of the price is being returned to customers. Result markets on major football carry the thinnest margins on any site because they are the most competitive; a twenty-runner outright or a novelty market carries a much wider one, because pricing a large field accurately is harder and the book has to allow for that.
Why prices move
Two forces, already mentioned across the sports pages and worth stating once properly.
Information
Team news, going, weather, a withdrawal, an injury in the warm-up. Anything that changes the underlying chance changes the price that describes it, and the largest single information event in most sports is the confirmed line-up about an hour before the start.
Liability
A bookmaker holding a large position on one outcome shortens it to discourage more of the same and lengthens the alternatives. That is balancing rather than prediction. It is why a price can move without any news, and why a shortening price is evidence about what other customers think rather than about what is going to happen.
Working out a return before you stake
Three calculations cover nearly every bet anybody places, and all three fit on the back of an envelope.
- Single, decimal. Stake multiplied by the price. £10 at 2.75 returns £27.50, of which £17.50 is winnings.
- Single, fractional. Stake divided by the second number, multiplied by the first, plus the stake. £10 at 5/2 is 10 ÷ 2 × 5 = £25 winnings, plus £10 back.
- Multiple. Multiply the decimal prices together, then by the stake. Three legs at 2.00, 1.50 and 3.00 give 9.00, so £10 returns £90.
The slip does all of this for you, but doing it once by hand is how the relationship between a price and a return stops being abstract. The bet slip page covers what each field on it means.
Odds-on, odds-against and what people get wrong
Two persistent misunderstandings are worth naming, because both of them cost money.
Short prices are not safe
A 1/5 shot implies an 83 per cent chance, which means it loses roughly one time in six. Backing five of them in a row at that price and losing once wipes out the profit from the other four. Short prices are not a way of avoiding risk; they are a way of accepting a small return in exchange for a high strike rate, and the arithmetic has to work over a season rather than over an afternoon.
Long prices are not value
A 50/1 shot is priced at 50/1 because its chance is around two per cent. Value has nothing to do with the size of the number and everything to do with whether the implied chance is lower than the real one, which is a judgement about the event rather than about the price. Most long prices are long for the reason they appear to be.
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Common questions
What does 5/2 mean?
You win five for every two staked, plus the stake back. A £10 bet returns £35. In decimals it is 3.50.
How do I convert fractions to decimals?
Divide the fraction and add one. 5/2 is 2.5 plus 1 = 3.50. 4/6 is 0.667 plus 1 = 1.67.
What chance does a price imply?
One divided by the decimal price. 4.00 implies 25 per cent. Adding up every outcome gives more than 100 per cent, and the excess is the bookmaker’s margin.
Can I switch to decimal odds?
Yes, in account settings. The change applies across the site and the app immediately.
Why did the price change after I looked at it?
Either new information arrived or money moved the market. Both are normal, and the slip will tell you if the price moved while you were confirming.