I occasionally use Betfair.

Here's a quite rundown of how decimal odds are converted to fractional:

**Fractional Odds to Implied Probability**

Say you have the odds of 9/4 or 4/5 what would be the implied probability of

each?

To convert take the denominator and divide it by the numerator plus the

denominator. Then multiplying by 100. So:

9/4 = 4/(4+9) = 4/13 = .3077 = 30.8%

4/5 = 5/(4+5) = 5/9 = .5556 = 55.56%

Note the book percentage is the sum of these implied probabilities. In

this case it's 106.32%.

**Implied Probability to Decimal Odds**

The decimal odds are calculated by dividing 1 by the implied probability (as

a decimal:

So for 9/4 (an implied probability of .3077) the decimal odds would be;

1/.3077 = 3.25

and for 5/9 (an implied probability of .5556)

1/.5556 = 1.80