Boneyard Tools

Decimal, fractional and American odds explained

How decimal, fractional and American odds each express the same price, how to convert between them, and what implied probability tells you.

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Decimal odds

Decimal odds are the most direct format because they state the total return per unit staked, including your stake back. A price of 6.0 means a 1 unit bet returns 6 units in total, which is 5 units of profit plus your original 1. This makes comparing prices easy: the bigger the decimal, the bigger the payout and the longer the odds. To find your profit, subtract 1 from the decimal, and to find implied probability, divide 100 by it.

Fractional odds

Fractional odds, long favoured in the UK and Ireland, describe profit relative to stake. A price of 5/1 (said five to one) means you win 5 units of profit for every 1 unit staked, so the total return is 6 units, matching decimal 6.0. A price of 1/2 is odds on, meaning the outcome is a favourite: you stake 2 to win 1. Because these fractions use whole numbers, an awkward decimal price is usually shown as the nearest simple fraction rather than an exact figure.

American moneyline odds

American odds are built around a 100 unit reference. A positive number such as +500 tells you the profit on a 100 stake, here 500, which again equals decimal 6.0. A negative number such as -150 tells you how much you must stake to win 100, so you risk 150 to profit 100, matching decimal 1.67. Favourites carry negative odds and underdogs carry positive odds, and the crossover point, even money, is +100 or -100, both equal to decimal 2.0.

Implied probability and the margin

Every price implies a probability of winning, found by dividing 100 by the decimal odds. Decimal 2.0 implies 50 percent, 6.0 implies about 16.67 percent, and 1.5 implies about 66.67 percent. If you add up the implied probabilities of every outcome in a market, the total exceeds 100 percent, and that overround is the bookmaker's built in margin. Comparing implied probabilities across books is a quick way to spot which one is offering the better value on a given selection.

Frequently asked questions

Do all three formats describe the same bet?

Yes. Decimal 6.0, fractional 5/1 and American +500 are the same price expressed three ways, and they all imply the same probability of about 16.67 percent. Formats are just regional conventions.

What does odds on mean?

Odds on describes a strong favourite whose profit is smaller than the stake, such as fractional 1/2 or decimal 1.5. In American terms these are negative prices like -200, where you must risk more than 100 to win 100.