Type a price into any one of the three fields – decimal, fractional or American – and the converter fills in the other two, along with the implied probability. 2.50, 6/4 and +150 are three ways of writing one bet at one price. The 40% underneath them is the part that decides whether the price is worth taking.
What Each Format Is Counting
Decimal odds count total return per unit staked. A price of 2.50 returns 2.50 for every 1 risked, made up of your 1 back plus 1.50 profit.
Fractional odds count profit against stake and ignore the stake return. 6/4 pays 6 profit for every 4 risked, which is the same 1.50 profit per 1 as the decimal version.
American odds anchor everything to 100. A positive number is profit on a 100 stake, so +150 wins 150. A negative number is the stake needed to win 100, so -125 risks 125 for a 100 return. Prices shorter than evens go negative, prices longer than evens go positive.
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 1.50 | 1/2 | -200 | 66.7% |
| 1.80 | 4/5 | -125 | 55.6% |
| 2.00 | 1/1 | +100 / -100 | 50.0% |
| 2.50 | 6/4 | +150 | 40.0% |
| 3.00 | 2/1 | +200 | 33.3% |
| 3.75 | 11/4 | +275 | 26.7% |
| 5.00 | 4/1 | +400 | 20.0% |
| 10.00 | 9/1 | +900 | 10.0% |
A Worked Example
Three prices, each shown in all four columns.
- 2.50 decimal = 6/4 fractional = +150 American = 40% implied.
- 1.80 decimal = 4/5 fractional = -125 American = 55.6% implied.
- 3.75 decimal = 11/4 fractional = +275 American = 26.7% implied.
The arithmetic behind the first row: 2.50 sits above 2.00, so the American conversion is (2.50 – 1) × 100 = +150. Strip the stake for the fraction and 2.50 – 1 = 1.50, written as 6/4. Divide 1 by 2.50 and you get 0.40, the 40% break-even win rate the price is asking for.
The 1.80 row crosses the evens line, so American flips negative: -100 ÷ (1.80 – 1) = -125.
Using the Output
Implied probability is the column that does the work. A price of 3.75 needs the bet to land 26.7% of the time to break even, and your own estimate against that number is your edge. The Implied Probability Calculator handles that step on its own if the conversion is not what you came for.
For one-way jobs, the directional pages carry their own reference tables: Decimal to American, American to Decimal, Decimal to Fractional, Fractional to Decimal, American to Fractional and Fractional to American. Football bettors here work in decimal day to day, since exchange ticks and EV maths both run on it.
What Conversion Cannot Do
Converting a price does not improve it. The bookmaker margin sits inside the number and travels with it through every format, which is why a 1X2 market at 2.50 / 3.40 / 2.90 adds up to 103.89% rather than 100%. The Hold / Vig Calculator measures that overround.
Fractional odds are quoted from a conventional ladder rather than from exact arithmetic. 2.375 converts to 11/8 cleanly, but plenty of decimal prices land between the rungs a bookmaker prints, and the board shows the nearest one.
American odds have a gap at the evens line. Nothing is quoted between -100 and +100, because both ends of that gap mean the same thing: risk 100 to win 100. A decimal price of 2.00 can appear as either.
Further Reading
- All betting calculators: the full library of 34 free tools
- Glossary: the terms you will see across Gecko Edge
- Why your betting lines move and where the expected value hides
Which odds format is the most accurate?
All three carry identical information, so accuracy is not the difference. Decimal is the most precise in practice, because fractional prices come from a fixed ladder and American odds round to whole numbers. Decimal also makes multiplication straightforward, which matters for accumulators and for any expected value calculation.
How do I convert odds to a percentage?
Divide 1 by the decimal price and multiply by 100. A price of 4.00 gives 1 ÷ 4.00 = 25%. From fractional, add the two parts and divide the denominator by the total, so 3/1 becomes 1 ÷ 4 = 25%. Positive American odds use 100 ÷ (odds + 100).
Why do UK bookmakers still use fractional odds?
Fractional pricing predates decimal display in British betting shops and has stayed on horse racing boards and in television coverage. Most UK online books now let you switch the display to decimal in account settings, and every exchange quotes decimal by default because prices move in small increments that fractions handle badly.
What does +100 mean in American odds?
+100 means a 100 stake wins 100 profit, the same as evens, 1/1 fractional or 2.00 decimal. It marks the boundary in the American system: anything longer runs positive, anything shorter runs negative. Some books print -100 for the same price, which describes the identical bet from the stake side.