Odds tell you two things: how much you will be paid if your bet wins, and roughly how likely the bookmaker thinks that is. British betting shops display odds as fractions, most websites let you switch to decimals, and both are just different ways of writing the same number. This guide explains how to read each format, convert between them, and work out a return in your head.
Fractional odds
Fractional odds are written as two numbers separated by a slash, such as 5/1, 11/8 or 1/3. Read the slash as “to”: five to one, eleven to eight, one to three.
The number on the right is the stake; the number on the left is the profit you make if you win. So:
- 5/1: stake £1, win £5 profit, and get your £1 stake back. Total return £6.
- 11/8: stake £8, win £11 profit, plus your £8 back. Total return £19. For a £1 stake, that is £1.375 profit and £2.375 back.
- 1/3: stake £3, win £1 profit, plus your £3 back. Total return £4.
When the left number is bigger, the selection is the outsider and you win more than you stake. When the right number is bigger, the selection is the favourite and you win less than you stake; these are called “odds on”. Evens (sometimes written 1/1 or Evs) means you win exactly what you stake.
To calculate your return from any fraction: divide the left number by the right, multiply by your stake, and add the stake back.
Return = stake × (left ÷ right) + stake
For £10 at 7/2: 7 ÷ 2 = 3.5; 3.5 × £10 = £35 profit; add the £10 stake for a return of £45.
Common fractional prices
Bookmakers use a traditional set of fractions rather than every possible number. The ones you will see most often, from shortest to longest, are:
| Odds | £10 stake returns | Roughly how often it should win |
| 1/5 | £12.00 | 5 in 6 |
| 1/2 | £15.00 | 2 in 3 |
| 4/6 | £16.67 | 3 in 5 |
| Evens | £20.00 | 1 in 2 |
| 6/4 | £25.00 | 2 in 5 |
| 2/1 | £30.00 | 1 in 3 |
| 7/2 | £45.00 | 2 in 9 |
| 5/1 | £60.00 | 1 in 6 |
| 10/1 | £110.00 | 1 in 11 |
| 33/1 | £340.00 | 1 in 34 |
| 100/1 | £1,010.00 | 1 in 101 |
A few conventions are worth knowing. Prices between evens and 2/1 tend to move in eighths and quarters (11/8, 6/4, 13/8, 7/4, 15/8). “Odds against” prices of 2/1 and above move in halves, then whole numbers, then bigger steps (5/1, 11/2, 6/1, 13/2, 7/1, 8/1, 9/1, 10/1, 11/1, 12/1, 14/1, 16/1, 20/1). You will rarely see 13/1 or 15/1 in a shop.
Decimal odds
Decimal odds, common online and standard across Europe, express the total return per £1 staked, including the stake. So 5/1 is 6.00, evens is 2.00, and 1/3 is 1.33.
Return = stake × decimal odds
For £10 at 4.50: £45 back, of which £35 is profit. The number is easier to multiply and easier to compare, which is why odds comparison sites prefer it. The drawback is that decimals include the stake, so a decimal of 1.20 is a profit of only 20p per pound, not £1.20.
Converting between the two
- Fraction to decimal: divide the left number by the right, then add 1. 11/8 → 11 ÷ 8 = 1.375, + 1 = 2.375 (usually shown as 2.38).
- Decimal to fraction: subtract 1, then express as a fraction. 3.50 → 2.50 → 5/2. 1.80 → 0.80 → 4/5.
Our odds converter does this for you and also shows the American (moneyline) format used in the United States.
Implied probability
Odds are also an estimate of chance. To find the probability implied by a price, divide the stake by the total return:
Implied probability = right ÷ (left + right)
At 5/1, that is 1 ÷ 6 = 16.7%. At 4/6, it is 6 ÷ 10 = 60%. For decimals, the calculation is simply 1 ÷ decimal odds: 1 ÷ 6.00 = 16.7%.
Implied probability is what makes odds useful for judgement rather than just arithmetic. If you think a horse has a one in four chance (25%) and the shop offers 5/1 (16.7%), the price is bigger than your estimate and the bet has value in your view. If the shop offers 2/1 (33%), it does not. Whether your estimate is any good is a different question, but this is the comparison every serious punter is making.
The overround
Add up the implied probabilities of every runner in a race and you will get more than 100%. On a typical horse race the total is 110% to 125%; on a football match it is closer to 105%. The excess is the bookmaker’s margin, known as the overround, and it is how the shop makes money regardless of the result. A market with a lower overround offers better prices across the board, which is one reason to compare bookmakers before placing a large bet.
Prices that move
Odds in a shop change right up to the start of an event, as money comes in and as the bookmaker’s own view changes. When you hand in a slip you can take the price shown at that moment, which is then fixed on your receipt whatever happens afterwards, or you can take the starting price (SP) on racing, the official odds at the off. Where a shop offers Best Odds Guaranteed you get the better of the two. Our guide to how betting shops work covers this.
Working out a return quickly
A few shortcuts for the counter:
- Whole-number odds (2/1, 5/1, 10/1): multiply the stake by the left number for profit; add the stake for the return.
- Odds-on prices: think of the fraction as a percentage of the stake. 4/6 pays two thirds of the stake as profit; 1/2 pays half.
- Eighths and quarters: work out the whole number, then the fraction. 13/8 on £8 is £13 profit, so on £10 it is £13 × 1.25 = £16.25.
Or use the bet calculator, which handles singles, each-way, accumulators and Rule 4 deductions.