Understanding Betting Odds

Every betting market is just odds in one of three formats. Once you can read all three and convert them to a percentage, you can compare any price across any bookmaker.

The three odds formats

Decimal odds (2.50) show your total return per unit staked. Fractional odds (3/2) show profit relative to stake. American odds (+150 / -200) show how much you win on 100, or how much you must stake to win 100.

They all describe the same thing. 2.50 decimal = 3/2 fractional = +150 American. Pick the format you find easiest and convert the rest to it.

Converting odds to a probability

For decimal odds, divide 1 by the number: 1 ÷ 2.50 = 40%. This 'implied probability' is the bookmaker's estimate of the outcome, plus their margin.

Comparing that implied probability with your own estimate is the whole basis of value betting — back outcomes where you think the true chance is higher than the odds suggest.

FAQ

What is the easiest odds format to understand?

Decimal odds are the simplest: the number is your total return per 1 unit staked. Odds of 2.50 return 2.50 for every 1 staked, including your stake.

How do I convert American odds to decimal?

For positive odds: (American ÷ 100) + 1, so +150 = 2.50. For negative odds: (100 ÷ American) + 1, so -200 = 1.50.