Odds

Odds are the price attached to an outcome. They show what an operator believes the chance of that outcome to be and how much a winning bet returns. The same price can be written three ways: decimal (2.50), fractional (3/2) and American (+150). Converting odds into implied probability is straightforward with decimals, since you divide one by the price, so 2.50 implies 40%. Add up the implied probabilities across a full market and the total exceeds 100%, because the bookmaker's margin, known as the overround, is built into every quoted price. Short odds mark a favourite and long odds an outsider, and prices move as money and news arrive. Odds are a price rather than a prediction, and that built-in margin means the long-run advantage sits with the operator, not the bettor.