Bet Fair

Posted by Andy Gavin on Sun, 2006-03-05 19:40

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