How Betting Odds Work: Fractional, Decimal and Implied Probability
Odds tell you two things: how much a winning bet pays, and how likely the bookmaker thinks the outcome is. Here is how to read them in every format you will come across.
Fractional odds
Fractional odds are the traditional British format, and you'll still see them on racecards and on most bookmakers' horse racing pages. The first number is what you win; the second is what you stake to win it.
- 5/2 means you win £5 for every £2 you stake.
- 2/1 means you win £2 for every £1 you stake.
- Evens (1/1) means you win the same amount you stake.
Your stake comes back on top of the winnings. So a winning £10 bet at 5/2 returns £35: £25 in winnings plus your £10 stake.
When the first number is smaller than the second, the price is "odds-on". At 1/2, a £10 bet wins £5 and returns £15. Odds-on prices are shown for outcomes the bookmaker thinks are more likely than not.
Decimal odds
Decimal odds show the total return for every £1 staked, including the stake. To work out a return, multiply your stake by the price.
| Fractional | Decimal | A £10 bet returns |
|---|---|---|
| 1/2 | 1.50 | £15.00 |
| Evens | 2.00 | £20.00 |
| 6/4 | 2.50 | £25.00 |
| 2/1 | 3.00 | £30.00 |
| 5/2 | 3.50 | £35.00 |
| 10/1 | 11.00 | £110.00 |
To convert fractional odds to decimal, divide the first number by the second and add 1. Five divided by two is 2.5, plus 1 gives 3.50.
Decimal odds make life easier when you compare prices or work out multiples, because you simply multiply the decimals together. Most UK bookmakers let you switch formats in your account settings.
American odds
American, or moneyline, odds use a plus or minus sign:
- A positive number shows what you win from a £100 stake. +250 means £100 wins £250, the same price as 5/2.
- A negative number shows what you must stake to win £100. -200 means you stake £200 to win £100, the same price as 1/2.
You're unlikely to need them on a UK site, but they turn up in coverage of American sports.
Odds as implied probability
Every price can be turned into the probability the bookmaker is implying:
- Decimal odds: divide 1 by the odds. 3.00 becomes 1 ÷ 3, or 33.3%.
- Fractional odds: divide the second number by the sum of both numbers. 2/1 becomes 1 ÷ (2 + 1), or 33.3%.
So 2/1 and 3.00 both imply a one-in-three chance, and evens implies 50%. If you think an outcome is more likely than the odds suggest, the price looks generous to you; if you think it's less likely, it doesn't. That's always a judgement call, and the bookmaker's prices already reflect a great deal of information.
The bookmaker's margin
Add up the implied probabilities for every outcome in a market and the total comes to more than 100%. The extra is the bookmaker's margin, often called the overround.
Take a football match priced like this:
| Outcome | Decimal odds | Implied probability |
|---|---|---|
| Home win | 2.10 | 47.6% |
| Draw | 3.40 | 29.4% |
| Away win | 3.60 | 27.8% |
| Total | 104.8% |
The 4.8% above 100% is built into the prices. It's how bookmakers stay profitable across thousands of bets, and it's why comparing prices between bookmakers is worth a minute of your time: a smaller margin means more of every pound staked goes back to winning bets.
Converting odds
You don't need to do any of this in your head. Our converter switches between fractional, decimal and American odds and shows the implied probability as you type:
Odds converter
A £10 bet at 5/2 returns £35.00, which is £25.00 profit plus your £10 stake.
Common odds conversion table
| Fractional | Decimal | American | Implied probability |
|---|---|---|---|
| 1/4 | 1.25 | -400 | 80.0% |
| 1/2 | 1.50 | -200 | 66.7% |
| 4/6 | 1.67 | -150 | 60.0% |
| 10/11 | 1.91 | -110 | 52.4% |
| Evens (1/1) | 2.00 | +100 | 50.0% |
| 6/5 | 2.20 | +120 | 45.5% |
| 5/4 | 2.25 | +125 | 44.4% |
| 6/4 | 2.50 | +150 | 40.0% |
| 7/4 | 2.75 | +175 | 36.4% |
| 2/1 | 3.00 | +200 | 33.3% |
| 9/4 | 3.25 | +225 | 30.8% |
| 5/2 | 3.50 | +250 | 28.6% |
| 3/1 | 4.00 | +300 | 25.0% |
| 7/2 | 4.50 | +350 | 22.2% |
| 4/1 | 5.00 | +400 | 20.0% |
| 5/1 | 6.00 | +500 | 16.7% |
| 6/1 | 7.00 | +600 | 14.3% |
| 8/1 | 9.00 | +800 | 11.1% |
| 10/1 | 11.00 | +1000 | 9.1% |
| 20/1 | 21.00 | +2000 | 4.8% |
| 33/1 | 34.00 | +3300 | 2.9% |
| 50/1 | 51.00 | +5000 | 2.0% |
| 100/1 | 101.00 | +10000 | 1.0% |
For illustration only. Returns depend on the operator's settlement rules, so always check your bet slip and the offer terms.
For full returns on singles, doubles and full-cover bets, use the bet calculator. If a bookmaker boosts a price, our guide to enhanced odds explains how the boosted winnings are paid.
Putting it into practice
- Check the odds format before you place a bet, especially on racing, where fractional odds are still the norm.
- Use implied probability to compare a price with your own view of an event.
- Remember the margin: across a whole market, the odds always add up to more than 100%.
When you're ready to look at markets, our guides to football betting and horse racing betting explain the most popular bet types, and the betting hub compares the current welcome offers from our featured bookmakers.
Keep it fun
Set a budget before you play, never chase losses and take regular breaks. Gambling should never be a way to make money. Free, confidential help is available from GamCare or the National Gambling Helpline on 0808 8020 133.
