Decimal vs Fractional vs American Odds
Three formats, one piece of information. Decimal, fractional and American odds all express exactly the same thing — probability and payout — just written differently. This guide explains how each works, how to calculate returns in all three, how to convert between them, and which format suits different types of bettor.
Why Three Formats Exist
Decimal, fractional and American odds are not different types of bet — they are three different ways of writing down exactly the same number. A bet at decimal 3.00, fractional 2/1 and American +200 is identical in every way.
Different formats emerged in different parts of the world and became entrenched through habit and tradition. Fractional odds developed in Britain and Ireland, where horse racing dominated betting culture for centuries. Decimal odds emerged as the standard for continental European bookmakers and online platforms where simplicity of calculation mattered. American odds (moneyline) evolved from US sports betting culture where point spreads and totals are also common.
Today, most online bookmakers offer all three and let you switch between them freely in your account settings. Understanding all three means you'll never be confused by a price regardless of where you're betting — and you'll be able to quickly compare odds across platforms that use different defaults.
Decimal Odds — How They Work
Decimal odds are the most straightforward format. They're displayed as a single number — such as 2.50, 4.00 or 1.33 — and the calculation is a single multiplication.
Total return = Stake × Decimal odds
Profit = Stake × (Decimal odds − 1)
Your stake is always included in the return figure — not added on top.
The key thing to remember with decimal odds is that the figure already includes your stake. Odds of 3.00 don't mean you win three times your stake in profit — they mean your total return is three times your stake, which is your original stake plus twice your stake in profit.
Decimal Odds — Worked Examples
Odds: 1.50 (odds-on)
£20 stake
Return: £20 × 1.50 = £30
Profit: £30 − £20 = £10
Implied probability: 66.7%
Odds: 2.00 (evens)
£20 stake
Return: £20 × 2.00 = £40
Profit: £40 − £20 = £20
Implied probability: 50.0%
Odds: 6.00 (outsider)
£20 stake
Return: £20 × 6.00 = £120
Profit: £120 − £20 = £100
Implied probability: 16.7%
Key Reference Points for Decimal Odds
Odds-On (Favourite)
You profit less than your stake. The bookmaker considers this outcome more likely than not. Any decimal odds between 1.01 and 1.99 are odds-on.
Odds-Against (Underdog)
You profit more than your stake. The bookmaker considers this outcome less likely than not. Odds of exactly 2.00 are evens — profit equals stake.
Decimal odds are the preferred format for matched betting, trading and any situation where you need to calculate returns quickly across multiple bets. All of our betting calculators use decimal odds as their primary input format.
Fractional Odds — How They Work
Fractional odds are the traditional British and Irish format. They're written as two numbers separated by a slash — such as 5/1, 7/2 or 1/3. The format reads as "X to Y" — meaning you win X units for every Y units staked.
Profit = Stake × (Numerator ÷ Denominator)
Total return = Stake + Profit
Unlike decimal odds, your stake is NOT included in the fraction — it's
added back separately.
The fraction tells you purely about profit, not total return. At 5/1, for every £1 you stake you win £5 in profit — plus your £1 back. At 1/3, for every £3 you stake you win £1 in profit — plus your £3 back.
Fractional Odds — Worked Examples
Odds: 1/3 (odds-on)
£30 stake
Profit: £30 × (1÷3) = £10
Return: £30 + £10 = £40
Implied probability: 75.0%
Odds: 1/1 (evens)
£20 stake
Profit: £20 × (1÷1) = £20
Return: £20 + £20 = £40
Implied probability: 50.0%
Odds: 5/1 (outsider)
£20 stake
Profit: £20 × (5÷1) = £100
Return: £20 + £100 = £120
Implied probability: 16.7%
Odds-On vs Odds-Against in Fractional Format
Odds-On
When the numerator is smaller than the denominator, the selection is odds-on — you stake more than you profit. The bookmaker considers this outcome more likely to happen than not.
Odds-Against
When the numerator is larger than the denominator, the selection is odds-against — you profit more than you stake. The bookmaker considers this outcome less likely than not.
Fractional odds aren't always simple whole numbers. You'll often see prices like 11/8, 13/5 or 15/8 — particularly in horse racing. These are harder to calculate mentally. When in doubt, convert to decimal first using our Odds Converter.
American Odds — How They Work
American odds, also called moneyline odds, are standard across US sportsbooks and increasingly visible on international platforms. They're written as either a positive or negative number — such as +350 or −180 — and the sign fundamentally changes how you read them.
Underdogs — e.g. +350
Shows profit on a £100 stake.
+350 → bet £100, win £350 profit (£450 total return).
To scale: divide by 100, multiply by your stake.
£20 at +350 → profit = £20 × 3.50 = £70
Favourites — e.g. −180
Shows stake required to win £100 profit.
−180 → bet £180 to win £100 profit (£280 total return).
To scale: divide 100 by the number, multiply by stake.
£20 at −180 → profit = £20 × (100÷180) = £11.11
American Odds — Worked Examples
Odds: −300 (favourite)
£30 stake
Profit: £30 × (100÷300) = £10
Return: £30 + £10 = £40
Equivalent decimal: 1.33
Odds: +100 (evens)
£20 stake
Profit: £20 × (100÷100) = £20
Return: £20 + £20 = £40
Equivalent decimal: 2.00
Odds: +500 (outsider)
£20 stake
Profit: £20 × (500÷100) = £100
Return: £20 + £100 = £120
Equivalent decimal: 6.00
American odds of +100 are evens — you profit exactly what you stake. Anything above +100 is odds-against (underdog). Anything with a minus sign is odds-on (favourite). There are no valid odds between +1 and +99, or between −1 and −99 — that range simply doesn't exist in this format.
All Three Formats Side by Side
This is the fastest way to build fluency across all three formats. The same odds, expressed in decimal, fractional and American — from short-priced favourite to big outsider.
Short Favourite
Decimal: 1.25
Fractional: 1/4
American: −400
Implied prob: 80.0%
£10 profit: £2.50
Solid Favourite
Decimal: 1.67
Fractional: 2/3
American: −150
Implied prob: 59.9%
£10 profit: £6.70
Even Money
Decimal: 2.00
Fractional: 1/1 (Evens)
American: +100
Implied prob: 50.0%
£10 profit: £10.00
Slight Underdog
Decimal: 2.50
Fractional: 6/4
American: +150
Implied prob: 40.0%
£10 profit: £15.00
Moderate Outsider
Decimal: 5.00
Fractional: 4/1
American: +400
Implied prob: 20.0%
£10 profit: £40.00
Big Outsider
Decimal: 21.00
Fractional: 20/1
American: +2000
Implied prob: 4.8%
£10 profit: £200.00
Notice how the relationship is consistent throughout: as odds shorten (more likely outcome), decimal odds approach 1.00, the fractional left number shrinks, and American odds go further negative. As odds lengthen (less likely outcome), all three move in the opposite direction.
How to Convert Between Formats
You can convert between any format using simple arithmetic. The quickest route is always to convert to decimal first, then to your target format.
Divide numerator by denominator, then add 1.
5/2 → (5 ÷ 2) + 1 = 3.50
1/4 → (1 ÷ 4) + 1 = 1.25
Subtract 1 from the decimal, then express as a
fraction and simplify.
3.50 → 3.50 − 1 = 2.50 = 5/2
1.25 → 1.25 − 1 = 0.25 = 1/4
Positive: (American ÷ 100) + 1
+250 → (250 ÷ 100) + 1 = 3.50
Negative: (100 ÷ |American|) + 1
−400 → (100 ÷ 400) + 1 = 1.25
If decimal ≥ 2.00: (Decimal − 1) × 100
3.50 → (3.50 − 1) × 100 = +250
If decimal < 2.00: −100 ÷ (Decimal − 1)
1.25 → −100 ÷ (1.25 − 1) = −400
Use our free Odds Converter — enter any odds in any format and instantly get all three formats plus the implied probability. No arithmetic required.
Which Format Should You Use?
There's no universally right answer — but there are clear reasons why certain formats suit certain bettors and situations better than others.
Use Decimal If...
You bet online regularly, use calculators or matched betting tools, want the simplest return calculation, or are new to betting. Decimal is the easiest to work with mathematically and is the global online standard.
Use Fractional If...
You grew up with British betting culture, follow horse racing closely, or bet in shops. Fractional odds are intuitive once learned — seeing 5/1 and instantly knowing you win five times your stake is very natural for experienced UK bettors.
Use American If...
You use US sportsbooks, bet on American sports (NFL, NBA, MLB, NHL), or need to communicate with American bettors. On US platforms you often have no choice — American odds are the default and sometimes the only option available.
Learn All Three
In practice the best approach is to understand all three well enough to read any odds you encounter, then work in whichever format your bookmaker defaults to. Switching formats mid-bet increases the chance of calculation errors.
Most online bookmakers let you switch between decimal, fractional and American in your account settings — usually under "Settings" or "Preferences." On mobile apps it's typically in the profile menu. The change applies immediately across all markets.
Common Questions
No — the format has no effect on the value of the bet. Decimal 3.00 and fractional 2/1 and American +200 are all exactly the same odds. The format is purely a display convention. What matters is the number itself and whether it represents fair value — not which format it's shown in.
Fractional odds were traditionally displayed in simple fractions, but as odds have become more precisely calibrated — especially in horse racing — the fractions have become less intuitive. 11/8 and 13/5 are legitimate fractions that simply can't be simplified further into round numbers. When you see these, it's easiest to convert to decimal: 11/8 → (11÷8)+1 = 2.375, and 13/5 → (13÷5)+1 = 3.60. Our Odds Converter handles any fractional input instantly.
Moneyline (American odds) is simply betting on who wins — no margin of victory required. Spread betting adds a handicap: the favourite must win by more than a set margin, and the underdog must lose by less than that margin (or win outright) for the bet to pay out. Spread bets use a points spread rather than moneyline odds and are common in American football, basketball and baseball. The two are different bet types, not just different odds formats.
No. The bookmaker's margin (overround) is built into the underlying odds number — it exists regardless of which format is displayed. Showing odds as decimal 1.91 or fractional 10/11 or American −110 is the same price with the same margin. The format is cosmetic. See our guide on What Is Overround? for a full explanation of how bookmaker margin works.
Betfair and most major exchanges default to decimal odds, which makes sense given that exchanges are used heavily by matched bettors and traders who need quick mental arithmetic. Betfair does allow you to switch to fractional in settings, but decimal is far more common among active exchange users. American odds are rarely if ever offered on UK/European exchanges as a display option.
Want to convert between formats instantly without doing the maths? Our free Odds Converter handles decimal, fractional and American — plus implied probability — in a single click.
Try the Odds Converter →