Enter the two halves of a fractional price and the converter returns the decimal equivalent and the implied probability. Divide the numerator by the denominator, then add 1 for the stake decimal odds include. A price of 11/8 gives 1.375 of profit, so the decimal figure is 2.375.
From Board Price to Exchange Price
Fractions were built for a betting shop, where a settler reads 11/8 and works out the return by hand. Exchange screens were built for arithmetic, and they show 2.375 because that number multiplies straight into a stake.
The conversion is one division and one addition: (numerator ÷ denominator) + 1. Older racing prices work the same way, which is how 100/30 arrives at 4.33.
| Fractional | Decimal | Implied probability |
|---|---|---|
| 1/5 | 1.20 | 83.3% |
| 2/7 | 1.29 | 77.8% |
| 8/13 | 1.62 | 61.9% |
| 5/6 | 1.83 | 54.5% |
| 5/4 | 2.25 | 44.4% |
| 15/8 | 2.875 | 34.8% |
| 9/2 | 5.50 | 18.2% |
| 20/1 | 21.00 | 4.8% |
A Worked Example
Two board prices, one modern and one from the older racing ladder.
- 11/8: 11 ÷ 8 = 1.375 of profit per 1 staked, plus the stake, for 2.375 decimal.
- 100/30: 100 ÷ 30 = 3.33 of profit per 1 staked, plus the stake, for 4.33 decimal.
Test the first one against a stake. At 11/8 a 40 bet wins 55 and returns 95 in total. Run it in decimal instead: 40 × 2.375 = 95, with the profit falling out of the same multiplication. The second format skips a step, which is the whole reason exchanges and calculators use it.
What Decimal Makes Easier
Multiplication across legs. A treble at 2.00, 1.80 and 1.60 comes to combined odds of 5.76 in one calculation, and 50 staked returns 288.00 for 238.00 profit. The same treble in fractions takes three conversions before you can start. The Parlay Calculator handles the multiplication for you.
Laying, too. A lay at 2.50 carries a liability of stake × (2.50 – 1), so 100 laid risks 150 to win 100 before commission. The Back & Lay Calculator works that out from the decimal price, and no fractional equivalent of the calculation exists in common use.
Implied probability arrives with one division: 1 ÷ 2.375 = 42.1%. EV work runs on decimal for the same reason.
Where the Conversion Cannot Follow You
A fraction converts into decimal exactly, but the decimal you get will not always be available. Exchange ladders step in fixed increments, and a converted price such as 2.875 may sit between two rungs, leaving you to take the nearest one. Recurring conversions such as 100/30 face the same thing: 4.33 is a rounded version of 4.3333.
The bigger point is what conversion does not touch. Writing 5/6 as 1.83 leaves the bookmaker’s margin exactly where it was, and a two-way market at 1.90 and 1.90 still adds up to 105.26% whatever format it is displayed in. The Hold / Vig Calculator returns the 5.00% hold hiding inside that pair, and the No-Vig Calculator strips it out to show what the market thinks before the charge.
The converted figure also says nothing about whether the board price was worth taking. A converted 2.375 is a fact about display, and the probability underneath it stays a separate question.
Further Reading
- All betting calculators: the full library of 34 free tools
- Glossary: the terms you will see across Gecko Edge
What is 11/8 in decimal odds?
11/8 converts to 2.375. Divide 11 by 8 for 1.375 of profit per unit staked, then add 1 for the stake that decimal odds include. A 40 stake wins 55 and returns 95. The implied probability is 1 ÷ 2.375 = 42.1%.
What does 100/30 mean?
100/30 is an older racing price meaning 100 profit for every 30 staked, which reduces to 10/3 and converts to 4.33 in decimal. Boards still print it in the 100/30 form out of habit. The implied probability is 23.1%, so the price asks the runner to win roughly once in four.
How do I convert odds-on fractions like 4/7?
The same division applies. 4 ÷ 7 = 0.571 of profit per unit staked, plus 1 for the stake, giving 1.571. Odds-on prices always land between 1.00 and 2.00 in decimal, since the profit is smaller than the stake that produced it.
Which format do betting exchanges use?
Decimal, without exception on the major exchanges. Prices move in small increments that fractions handle badly, and every calculation on an exchange – liability, matched amounts, commission, cash-out value – runs on multiplication. Bookmaker apps usually offer a decimal setting in account preferences if you want one format across all your accounts.