Three ways of writing one price
A betting price tells you what is returned if an outcome happens. Different regions and bookmakers write that same information in three common styles: decimal, fractional and American. Decimal is often seen in continental Europe and many online markets, fractional is traditionally associated with the United Kingdom and Ireland, and American (or moneyline) odds are used in the United States. Whichever style you meet, the underlying price is the same; only the notation changes.
Decimal odds
Decimal odds show the total return per 1 staked, including the stake. A price of 2.50 returns 2.50 for each 1 staked, which is a profit of 1.50.
- Profit per 1 staked = decimal odds - 1
- Implied probability = 1 / decimal odds
At 2.50, the implied probability is 1 / 2.50 = 40%.
Fractional odds
Fractional odds show profit relative to stake. A price of 3/2 (read “three-to-two”) means a profit of 3 for every 2 staked.
- Decimal odds = 1 + numerator / denominator
- Implied probability = denominator / (numerator + denominator)
For 3/2: decimal = 1 + 3/2 = 2.50, and implied probability = 2 / 5 = 40%. A price of 1/1 is often called evens, meaning profit equal to stake.
A fraction with a larger denominator than numerator, such as 2/5, is sometimes called odds-on. The decimal is 1 + 2/5 = 1.40 and the implied probability is 5/7, about 71.4%. By contrast 5/2 gives decimal 3.50 and an implied probability of 2/7, about 28.6%. Mixing up 2/5 and 5/2 is a common slip.
American odds
American odds use a positive or negative number relative to a base of 100.
- A positive number such as +150 is the profit on a stake of 100. Decimal = 1 + 150 / 100 = 2.50.
- A negative number such as -200 is the stake needed to win a profit of 100. Decimal = 1 + 100 / 200 = 1.50.
Implied probability follows directly:
- For positive odds A: probability = 100 / (A + 100). For +150: 100 / 250 = 40%.
- For negative odds A (using its size without the minus sign): probability = A / (A + 100). For -200: 200 / 300, about 66.7%.
Going the other way from decimal odds d:
- If d is 2.00 or more, American = (d - 1) x 100. For 3.00: +200.
- If d is below 2.00, American = -100 / (d - 1). For 1.25: -100 / 0.25 = -400.
Quick-reference table
| 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% |
| 2.50 | 3/2 | +150 | 40.0% |
| 3.00 | 2/1 | +200 | 33.3% |
| 4.50 | 7/2 | +350 | 22.2% |
Check one row by hand: 4.50 minus 1 is a profit of 3.50 per 1 staked. That is 7/2 as a fraction, a profit of 350 on a stake of 100 (+350), and an implied probability of 1 / 4.50 = 22.2%.
Practical points and pitfalls
Rounding. Fractional prices are usually drawn from a standard set of fractions, so converting a decimal price to a fraction often gives only a close match. Decimal prices quoted to two places also hide small differences.
Probability is not the same as odds. A price of 3/1 describes a ratio of profit to stake, while the implied probability is 25%. The wider topic of odds conversion between ratios and percentages applies outside betting too, for example in dice and cards.
Implied probabilities include a margin. If you convert every price in a market into a percentage, the totals typically exceed 100% because of the bookmaker margin. That excess is a feature of how prices are set, not a conversion error.
Prices are not predictions. Converting a price to a percentage only translates the bookmaker’s quote. It does not say how likely an outcome actually is, and an implied 80% outcome still fails about one time in five. The wider picture of how to read betting odds as estimates, not facts, is worth keeping in mind.
Wagering can lead to losses and can become harmful. If gambling is causing you difficulty, a local support service can offer confidential help.