Odds are the probability of a betting proposition occurring. The format used to express this varies in different localities but the key types are fractional (e.g. 2/1), decimal (e.g. 3.0) and American or Moneyline (+200.00). Each type corresponds to a percentage, for example in the previous examples, the proposition has an implied 50% probability.
The percentage probability for fractional odds can be calculated by dividing the lower figure by the one above (1/2= 33%).
The percentage probability for decimal odds can be worked out by dividing 1 by the decimal (1/3.0= 33%)
The rules for Moneyline odds are more complex and depend on whether the odds are plus or minus, For plus, the formula is 100 / ( 'plus' moneyline odds + 100 ) (100 / 200 + 100 = 33%).