Betting odds explained: how to read fractional, decimal, and American odds
Last updated: April 2026
Betting odds tell you two things: how likely an outcome is and how much you'll win if it happens. The lower the odds, the more likely the outcome (and the smaller the payout). The higher the odds, the less likely (and the bigger the payout).
This guide explains all three formats in plain English with worked examples. No maths background needed. If you want to convert between formats or calculate returns instantly, our odds calculator does it automatically.
Try the Odds Converter Calculator → Work out your returns instantly with our free odds converter calculator.
What are betting odds?
Odds represent the relationship between the probability of an outcome and the payout a bookmaker offers. Three formats exist because different countries use different conventions: the UK uses fractional odds, Europe and Australia use decimal, and the United States uses American odds (also called moneyline).
All three express the same thing — just differently. A horse priced at 5/1 fractional is the same as 6.00 decimal and +500 American. The returns are identical no matter which format you read.
When you see odds on a betting site, they reflect two things: the bookmaker's estimate of how likely the outcome is, and the payout they're willing to offer. Lower odds (like 1/4 or 1.25) mean the outcome is considered likely — you won't win much, but you're more likely to win. Higher odds (like 20/1 or 21.00) mean the outcome is considered unlikely — but if it happens, the payout is substantial.
One important thing to understand upfront: bookmakers build a profit margin into every set of odds. This means the odds always slightly understate the true payout. That margin — called the overround or vig — is how bookmakers make money. More on this later.
Fractional odds explained
Fractional odds are the UK standard. You'll see them in betting shops, on horse racing cards, and across most UK bookmaker websites. They're written as two numbers separated by a slash: 5/1, 2/1, 1/4, 11/8, and so on.
How to read fractional odds
If you're wondering how to work out betting odds in the UK, fractional is the format you need to know. The first number is your potential profit and the second is your stake. At 5/1 ("five to one"), you win £5 for every £1 you stake. At 2/1, you win £2 for every £1. At 10/1, you win £10 for every £1.
What does odds on mean? When the second number is larger than the first — like 1/2, 1/4, or 4/6 — the outcome is priced as more likely than not. These are called odds-on prices or short odds. At 1/2 ("two to one on"), you stake £2 to win £1. At 1/4, you stake £4 to win £1.
The opposite is odds against — where the first number is larger, like 5/1 or 10/1. These are long odds, meaning the outcome is less likely but the payout is bigger.
What does evens mean? Evens (also written as 1/1 or "even money") means your profit equals your stake. A £10 bet at evens returns £20 — £10 profit plus your £10 back. It implies roughly a 50/50 chance.
How to calculate betting returns from fractional odds
The formula: Returns = Stake × (Numerator ÷ Denominator) + Stake
Worked example: £10 at 5/1 → (10 × 5) + 10 = £60 total returns (£50 profit + £10 stake back).
Another example: £10 at 1/4 → (10 × 0.25) + 10 = £12.50 total returns (£2.50 profit).
Horse racing betting odds explained
Horse racing is where you'll encounter fractional odds most often. A typical race card might show the favourite at 2/1, the second favourite at 5/1, a mid-range runner at 11/2, and an outsider at 25/1.
You'll also see SP (starting price) — this is the official odds at the time the race begins, as opposed to the price you took when you placed your bet. If you take a price early, you keep those odds regardless of how the SP moves. If you bet at SP, you get whatever the odds are at the off.
Common odds you'll see in horse racing include 4/6, 11/8, 7/2, 9/4, 100/30, and 13/8 — these are traditional bookmaker prices that don't always simplify neatly but are standard in the sport.
Common fractional odds at a glance
| Odds | £10 Stake Returns | Profit | Implied Probability |
|---|---|---|---|
| 1/5 | £12.00 | £2.00 | 83.3% |
| 1/2 | £15.00 | £5.00 | 66.7% |
| 4/6 | £16.67 | £6.67 | 60.0% |
| 1/1 (evens) | £20.00 | £10.00 | 50.0% |
| 2/1 | £30.00 | £20.00 | 33.3% |
| 5/1 | £60.00 | £50.00 | 16.7% |
| 10/1 | £110.00 | £100.00 | 9.1% |
| 20/1 | £210.00 | £200.00 | 4.8% |
| 50/1 | £510.00 | £500.00 | 2.0% |
Decimal odds explained
Decimal odds are the standard in Europe, Australia, and on betting exchanges like Betfair. They're written as a single number: 6.00, 3.50, 1.25, and so on.
How to read decimal odds
The number is your total return per £1 staked — including your stake. At 6.00, a £1 bet returns £6 total (£5 profit + £1 stake). At 1.50, a £1 bet returns £1.50 (50p profit). Anything below 2.00 is odds-on.
The key advantage of decimal over fractional: simplicity. To calculate returns, just multiply. No fractions, no mental arithmetic.
How to calculate returns from decimal odds
The formula: Returns = Stake × Decimal Odds
That's it. £10 at 6.00 = £60. £10 at 1.50 = £15. £10 at 3.50 = £35.
Decimal vs fractional: to convert fractional to decimal, divide the first number by the second and add 1. So 5/1 = (5 ÷ 1) + 1 = 6.00. And 1/4 = (1 ÷ 4) + 1 = 1.25.
Why betting exchanges use decimal odds
Betting exchanges — platforms where you bet against other people rather than against a bookmaker — use decimal odds because they make calculating lay bets (betting that something won't happen) and commission deductions much simpler. If you've used Betfair or Smarkets, you've used decimal odds.
American odds explained
American odds (also called moneyline odds) are the standard in the United States. They use positive and negative numbers: +500 or −200.
American betting odds explained — the plus and minus signs
If you've ever wondered what the plus and minus mean in betting, this is it:
Positive odds (+500): how much profit you make on a £100 stake. +500 means £500 profit on a £100 bet, giving £600 total returns.
Negative odds (−200): how much you need to stake to make £100 profit. −200 means you stake £200 to profit £100, giving £300 total returns.
The minus sign means the outcome is favoured (odds-on). The plus sign means it's the underdog (odds-against). The larger the negative number, the stronger the favourite. The larger the positive number, the longer the shot. The concept of using positive and negative numbers for odds originated in US horse racing and is now the standard format across all American sports betting.
How to calculate returns from American odds
Positive: Returns = Stake × (Odds ÷ 100) + Stake
Negative: Returns = Stake × (100 ÷ |Odds|) + Stake
Worked example: £10 at +500 → (10 × 5) + 10 = £60. That's the same as 5/1 fractional or 6.00 decimal — the returns are identical across all three formats.
Most UK punters won't encounter American odds often, but they appear on US-facing sites, some international betting exchanges, and in MMA and boxing markets. If someone mentions a "moneyline bet," they're using American odds.
Odds conversion table — all three formats
| Fractional | Decimal | American | £10 Returns | Implied Probability |
|---|---|---|---|---|
| 1/5 | 1.20 | −500 | £12.00 | 83.3% |
| 1/2 | 1.50 | −200 | £15.00 | 66.7% |
| 1/1 (evens) | 2.00 | +100 | £20.00 | 50.0% |
| 2/1 | 3.00 | +200 | £30.00 | 33.3% |
| 5/1 | 6.00 | +500 | £60.00 | 16.7% |
| 10/1 | 11.00 | +1000 | £110.00 | 9.1% |
| 20/1 | 21.00 | +2000 | £210.00 | 4.8% |
| 50/1 | 51.00 | +5000 | £510.00 | 2.0% |
To convert between any of these formats instantly — or to calculate returns for any stake — use our odds calculator.
What is implied probability — and why it matters
Implied probability converts odds into a percentage chance. The formula is straightforward: 1 ÷ decimal odds × 100.
At 5/1 (6.00 decimal), the implied probability is 1 ÷ 6.00 × 100 = 16.67%. This is the bookmaker's assessment of how likely the outcome is — or more precisely, the probability embedded in the price they're offering.
Why it matters for you
Implied probability lets you compare the bookmaker's assessment with your own. If you think an outcome has a 25% chance of happening but the implied probability is only 16.67%, that could be a value bet — the odds are more generous than the true likelihood suggests. If you think the chance is only 10%, the bookmaker is pricing it more generously than your own assessment, but you'd still expect to lose more often than you'd win.
Understanding implied probability is what separates informed betting from guesswork.
The overround — how do bookmakers make money?
Add up the implied probabilities of all outcomes in an event and they'll total more than 100%. The excess is the bookmaker's margin, also called the overround or vig (short for vigorish). This is how bookmakers guarantee a profit regardless of the result.
Example: a coin flip should be 50/50, but a bookmaker might offer 10/11 on both sides. Each outcome has an implied probability of 52.4%, totalling 104.8%. That 4.8% is the bookmaker's built-in profit — their cut on every market, win or lose.
A typical football match might have a total book of 104–106%. The lower the overround, the better value for bettors. Betting exchanges typically offer lower margins than traditional bookmakers because you're betting against other people, not the house. For more on how the house edge works across different games, see our house edge calculator. For a complete breakdown of how the house edge varies across every casino game, see our house edge explained guide.
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Written by
David Burke
David is a gambling industry analyst and poker player based between London, Spain, and Malta. He has spent over a decade observing the European betting and casino landscape, with particular expertise in odds, probability, game strategy, and how the bookmaking industry works. At WiseStaker, David writes guides on bet types, game rules, and the mathematics behind gambling.
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