Being able to convert fractional, percentage and American betting odds into decimal odds is vital when comparing prices quickly across online bookmakers and exchanges.
Betting sites offer a number of different odds formats. It’s vital, however, to understand that regardless of the odds format presented, the probability is always the same.
Converting fractional odds to decimal odds
You can convert fractional odds to decimals odds with this equation:
(numerator/denominator) + 1 = decimal odds
Using the starting price on Chic Theatre (36/5) to win at Towcester as an example:
The one added to the equation accounts for the return of stake which is not included in fractional odds, but is included in the return displayed by decimal odds.
Converting percentage odds to decimal odds
Decimal odds are simply inverted probabilities, which is why it’s so easy to calculate. This equation quickly converts percentages into decimal odds:
100 / implied probability = decimal odds
As an example let’s say you think Manchester United have a 68% chance of beating Sunderland at home. To calculate your decimal odds, you want to convert 68% into odds:
No addition is required for return of stake, as it is already included in the display of both percentage and decimal odds.
Converting American odds to decimal odds
Converting American odds into decimals can be done quickly with these calculations.
To convert positive American odds the equation is:
(American odds / 100) + 1 = Decimal odds
Let’s use the starting price offered on the Denver Broncos (+205) to win Super Bowl 50 as an example:
To convert negative American odds the equation is:
(100 / American odds) + 1 = Decimal odds
For favourites the Carolina Panthers, who started at -200:
As with the fractional odds conversion, the one is added in respect of the stake not being included in the return with American odds, but being included for decimals.
Apply this to betting
Now you have learnt how to convert fractional, percentage and American betting odds to decimal odds you have the necessary tools to compare all bookmaker and exchange prices quickly, irrespective of the format shown.