Sportsbooks express the same probability three different ways depending on who they serve and where they grew up. American odds dominate the United States. Decimal odds are the global online standard and what most professional bettors think in. Fractional odds are the historical UK and Irish racing format, still common at high-street bookmakers and racecourses.
Sportsbooks express the same probability three different ways depending on who they serve and where they grew up. American odds dominate the United States. Decimal odds are the global online standard and what most professional bettors think in. Fractional odds are the historical UK and Irish racing format, still common at high-street bookmakers and racecourses.
Mathematically all three are translations of one another — type a value into any one field of the Odds Converter and the other two appear instantly. Culturally each carries its own audience and its own learning curve. This post is the side-by-side: how each format works, where each is used, and which to use if you're starting out.
| Decimal | American | Fractional | Implied prob. | What a $100 bet returns (total) |
|---|---|---|---|---|
| 1.50 | −200 | 1/2 | 66.7% | $150 |
| 1.91 | −110 | 10/11 | 52.4% | $190.91 |
| 2.00 | +100 | 1/1 (Evens) | 50.0% | $200 |
| 2.50 | +150 | 3/2 (or 6/4) | 40.0% | $250 |
| 3.00 | +200 | 2/1 | 33.3% | $300 |
| 5.00 | +400 | 4/1 | 20.0% | $500 |
| 11.00 | +1000 | 10/1 | 9.1% | $1,100 |
American odds — also called moneyline odds — express the bet relative to a $100 unit.
+150 means $100 stake → $150 profit (and $100 stake back, for $250 total).−200 means bet $200 to win $100 (and $200 stake back, for $300 total).+100, −100, or "EVEN".The line at which a price flips from positive to negative is 50% — even money. Anything more negative than −100 is a favorite (over 50% implied chance); anything more positive than +100 is an underdog (under 50%).
For decimal ≥ 2.00 (underdog/longshot): - American = (decimal − 1) × 100 - 2.50 → +150. 3.00 → +200. 4.00 → +300.
For decimal < 2.00 (favorite): - American = −100 ÷ (decimal − 1) - 1.50 → −200. 1.40 → −250. 1.25 → −400.
Decimal odds express total return per unit staked, including the stake itself.
To American (decimal ≥ 2.00): subtract 1, multiply by 100. 2.50 → 150 → +150.
To American (decimal < 2.00): 100 ÷ (decimal − 1), put a minus sign. 1.50 → 100/0.5 = 200 → −200.
To fractional: subtract 1, express as fraction. 3.00 → 2/1. 2.50 → 3/2.
Fractional odds express profit per stake as a fraction. The traditional UK and Irish format, especially in horse racing.
3/2 = "win 3 for every 2 staked." A £10 bet wins £15 profit + £10 stake = £25 total.5/2 = "win 5 per 2 staked." 4/1 = "win 4 per 1 staked." 10/1 = "win 10 per 1 staked."1/2 = "win 1 for every 2 staked" (heavy favorite). 1/4 = "risk 4 to win 1" (very heavy favorite).5/1 directly tells you that £1 wins £5. Some bettors find this the most intuitive.11/4, 15/8, 13/8 because punters think in racing-traditional denominators. Mathematically 11/4 = 3.75 decimal, but the fraction is harder to compare than the decimal.3/2 and 6/4 are the same price. UK racing books commonly show 6/4 while online tables show 3/2. New punters double-take.11/4 vs 5/2. Convert both to decimal (3.75 vs 3.50) and the comparison becomes obvious. Decimal saves you a step.To decimal: numerator/denominator + 1. 3/2 → 1.5 + 1 = 2.50. 1/4 → 0.25 + 1 = 1.25.
To American (fraction ≥ 1/1): numerator × 100 ÷ denominator. 3/2 → 150.
To American (fraction < 1/1): −100 × denominator ÷ numerator. 1/4 → −400.
| Bet | American | Decimal | Fractional | Profit | Total return |
|---|---|---|---|---|---|
| Heavy favorite | −500 | 1.20 | 1/5 | £20 | £120 |
| Modest favorite | −150 | 1.667 | 4/6 (or 2/3) | £67 | £167 |
| Even money | +100 | 2.00 | 1/1 (Evens) | £100 | £200 |
| Modest underdog | +200 | 3.00 | 2/1 | £200 | £300 |
| Long shot | +500 | 6.00 | 5/1 | £500 | £600 |
| Very long shot | +2500 | 26.00 | 25/1 | £2,500 | £2,600 |
Use the Odds Converter to translate any price between formats and see your payout for any stake.
The honest answer: whichever format your sportsbook displays in is the one to learn first. The format isn't a strategic choice — it's a UI preference. The sportsbook's internal math is the same regardless of how it's presented.
That said:
Learn American first because every domestic broadcast, podcast, and sportsbook will default to it. Then learn decimal as a second language because you'll need it for arbitrage tools, betting exchanges, and any cross-border comparison.
Decimal is the path of least resistance. Most UK sportsbooks let you switch displays to decimal in account settings. Fractional is unavoidable if you bet horse racing — learn the common fractions (1/4, 1/3, 1/2, 4/6, 1/1, 5/4, 6/4, 7/4, 2/1, 5/2, 3/1, 4/1, 5/1, 10/1) and you can decode 95% of UK racing prices on sight.
Decimal. Nothing else has a meaningful share outside the U.S. and UK racing. Decimal is what every betting exchange, every sharp book, and every arbitrage tool speaks natively.
Decimal. The math is faster, the comparison across markets is easier, and your edge calculations (fair line, no-vig probability, Kelly fraction) all work on decimal natively. Sharps mentally translate American or fractional into decimal as a first step before doing anything else.
If you're new to one of the formats, the fastest way to internalize it is to convert between them until it's automatic. Try these without a calculator first, then check with the Odds Converter:
| Convert | Answer |
|---|---|
| +120 → decimal | 2.20 |
| +250 → decimal | 3.50 |
| −115 → decimal | 1.870 |
| 1.83 → American | −120 |
| 4.50 → American | +350 |
| 5/2 → decimal | 3.50 |
| 1/3 → decimal | 1.333 |
| 1.91 → fractional | 10/11 |
Aim for sub-5-second conversions on common values (anything in the −300 to +500 range). Get to that point and you'll never be lost at any sportsbook anywhere.
For the six specific direction pairs, we have dedicated pages with formula, full conversion table, and direction-specific FAQs:
Or just type any value into the Odds Converter and read the other two off instantly.