Each-Way AtlasGlossary: each-way, odds and racing terms
Implied probability
Implied probability is the chance that a price expresses, worked out as 1 divided by the decimal odds. It is not a forecast of the result, only the share a price represents before any margin is taken out. Fractional prices are converted on how to read odds. In UK betting it appears when odds are compared.
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What implied probability is
Every price carries a share. A shorter price shows a bigger share, and a longer price shows a smaller one.
The number is called implied because the bookmaker does not state it. You work it out from the price.
Why it matters: it turns odds into a common scale, so you can compare a fractional and a decimal price directly.
The short version: implied probability is the share a price expresses.
Two formulas
With decimal odds, divide 1 by the price. With fractional odds a/b, divide b by the sum of a and b. Both give the same share for the same price.
| Odds format | Implied probability |
|---|---|
| Decimal price O | 1 ÷ O |
| Fractional price a/b | b ÷ (a + b) |
| Link between the two | O = 1 + a ÷ b |
See decimal odds and fractional odds for each format.
The short version: use 1 divided by the decimal price.
What it is not
It is not a prediction. It does not say how likely a horse is to win, because it still contains the bookmaker's margin.
When the shares of all outcomes in a market are added, the total is above 100 per cent. That excess is the overround. The calculation on a real market is on the bookmaker margin claim.
The short version: a price's implied share includes the bookmaker's margin.
What we have and have not checked
The formulas are arithmetic. A primary source for the definition is still to be added.
| Fact to read | Where to read it | Status |
|---|---|---|
| A definition from a primary source | Regulator or operator help pages, dated | Not verified |
| The fractional and decimal conversion formulas as published | Primary source, with the date read | Not verified |
The short version: formulas are shown; sources are marked Not verified.
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