Odds Formats Explained: Decimal, Fractional, American and Implied Probability
Updated 2026-10-035 min read
Bookmakers show the same price in different formats depending on the country: decimal in Europe, fractional in the UK and Ireland, American (moneyline) in the US. They all say the same thing. The useful skill is converting any of them into an implied probability, because that is the number you compare with your own estimate.
The three formats
- Decimal (2.20): the total return per 1 staked, stake included. A 10 stake returns 22.
- Fractional (6/5): the profit relative to the stake, stake excluded. Staking 5 wins 6 in profit, 11 back in total.
- American (+120 or −200): a positive number is the profit on a 100 stake; a negative number is the stake needed to win 100.
Fractional n/m → decimal = 1 + n/m. American +A → decimal = 1 + A/100. American −A → decimal = 1 + 100/A. Implied probability = 1 / decimal.
Same price, three languages
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 1.25 | 1/4 | −400 | 80.0% |
| 1.50 | 1/2 | −200 | 66.7% |
| 2.00 | 1/1 | +100 | 50.0% |
| 2.20 | 6/5 | +120 | 45.5% |
| 2.50 | 3/2 | +150 | 40.0% |
| 4.00 | 3/1 | +300 | 25.0% |
Even money is decimal 2.00, fractional 1/1 and American +100. Everything below it is a favourite (negative American odds), everything above is an underdog (positive American odds).
Pick a format, type the odds, and see the other two formats and the implied probability.
Illustrative calculator. Results depend entirely on the numbers you enter.
Why implied probability is the number that matters
An implied probability is the chance the price asks you to believe. At 2.20 the price needs the event to happen more than 45.5% of the time just to break even. If your honest estimate is 50%, the price is generous; if it is 40%, it is not.
Remember that implied probabilities include the bookmaker's margin. For a full market they add up to more than 100%, so a single implied probability is slightly higher than the real chance the market assigns. Our guide on the bookmaker margin shows how to strip it out.
Frequently asked questions
How do you convert fractional odds to decimal?
Divide the numerator by the denominator and add 1. For example 6/5 gives 6 ÷ 5 + 1 = 2.20.
How do you convert American odds to decimal?
For positive odds, divide by 100 and add 1 (+120 gives 2.20). For negative odds, divide 100 by the number and add 1 (−200 gives 1.50).
How do you calculate implied probability from odds?
Divide 1 by the decimal odds. Odds of 2.20 imply 1 ÷ 2.20 = 45.5%.
Is the implied probability the real chance of winning?
Not exactly. It includes the bookmaker's margin, so for a whole market the implied probabilities add up to more than 100%.
More guides
- What Is a Value Bet? A Practical Guide With Real Numbers
- Bookmaker Margin (Overround) Explained: How to Calculate It
- Closing Line Value (CLV): The Best Test of Betting Skill
- Dropping Odds Explained: What a Falling Price Really Means
- Asian Handicap Quarter Lines (±0.25, ±0.75) Explained
- Kelly Criterion for Betting: How Much Should You Stake?
- Over/Under 2.5 Goals Explained: How the Market Works and How to Price It
- Both Teams to Score (BTTS) Explained: How to Estimate the Probability
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