How to read betting odds: American, decimal and fractional

Every sportsbook price is the same information written three ways: how much you win for a given stake, and by implication, how likely the book thinks the outcome is. American, decimal and fractional odds are different notations for that one number. Once you can move between them and convert any of them to a probability, the rest of betting arithmetic follows.

American odds

American odds are written as a positive or negative number relative to 100. A negative number is the amount you must risk to win 100. A positive number is the amount you win for risking 100.

• -150 means risk 150 to win 100. Your return if the bet wins is 250: the 100 profit plus your 150 stake back.
• +130 means risk 100 to win 130. Your return is 230.
• -110 is the standard price on a point spread or total. Risk 110 to win 100.
• +100, sometimes written as EVEN, means risk 100 to win 100.

Favourites carry negative numbers and underdogs carry positive ones. The further from 100 in either direction, the more lopsided the book considers the matchup.

Decimal odds

Decimal odds state the total return per unit staked, including the stake itself. A price of 2.50 returns 2.50 for every 1 staked: 1.50 profit plus the 1 stake. A price of 1.67 returns 1.67 per 1 staked, so 0.67 profit. Anything below 2.00 is a favourite; anything above is an underdog. Even money is exactly 2.00.

Decimal odds are the easiest format for arithmetic, which is why parlay calculators and most of the rest of this site's guides use them. To find a parlay price you multiply the decimal odds of each leg together. To find profit you subtract 1 and multiply by the stake.

Fractional odds

Fractional odds, common in UK racing, state profit relative to stake as a fraction. 5/1 (five to one) means 5 profit for every 1 staked. 1/2 (one to two, or two to one on) means 1 profit for every 2 staked. Evens is 1/1.

To convert a fraction to decimal odds, divide the numerator by the denominator and add 1. So 5/1 becomes 6.00 and 1/2 becomes 1.50.

Converting between formats

American to decimal

• Positive American odds: divide by 100 and add 1. +130 becomes 2.30.
• Negative American odds: divide 100 by the absolute value and add 1. -150 becomes 100 / 150 + 1 = 1.667.

Decimal to American

• Decimal 2.00 or higher: subtract 1 and multiply by 100. 2.30 becomes +130.
• Decimal below 2.00: divide -100 by (decimal minus 1). 1.667 becomes -100 / 0.667 = -150.

Implied probability

The most useful conversion is from odds to the probability the price implies. With decimal odds it is one step: divide 1 by the decimal price. A price of 2.50 implies 1 / 2.50 = 40%. A price of 1.667 implies 60%.

For American odds without converting first:

• Negative price: absolute value ÷ (absolute value + 100). -150 implies 150 / 250 = 60%.
• Positive price: 100 ÷ (price + 100). +130 implies 100 / 230 = 43.5%.

Implied probability is what lets you compare a price to your own view. If you think a team wins 65% of the time and the book is offering a price that implies 60%, the price is better than your estimate and the bet has positive expected value by your reckoning. If the book implies 70%, it does not.

Why the probabilities add to more than 100%

Convert both sides of any market and the probabilities sum to more than 100%. Two sides at -110 imply 52.4% each, 104.8% together. That excess is the book's hold: its margin on the market, collected regardless of result. The size of the hold varies by sport, by market and by book, and a bettor comparing prices is really comparing holds. A market at -105 on both sides carries roughly half the hold of one at -110.

Reading a line

A typical NFL line reads something like: Team A -3.5 (-110), Team B +3.5 (-110), total 47.5 (over -110, under -110), moneyline Team A -180, Team B +155.

• The spread is -3.5 and +3.5. Team A must win by 4 or more to cover; Team B covers if it loses by 3 or fewer or wins. The -110 in brackets is the price on each side.
• The total is 47.5. Over wins if the combined score is 48 or more, under if 47 or fewer. The half point means no tie.
• The moneyline is the price to pick the winner with no spread. Team A at -180 implies about 64%; Team B at +155 implies about 39%. Together they imply 103%, so the hold on this market is about 3%.

Once a line reads like that, every other format on every other site is the same information in a different notation. The number to carry in your head is the implied probability. The rest is presentation.