Odds Converter

Six notations, one number. American odds, decimal odds and fractional odds are three ways of writing the same thing, and the probability underneath is what all three are really quoting.

Type a price in whichever notation your book uses and read it in the rest, along with the win rate it implies and what your stake returns.

What Each Notation Is Saying

All six formats answer the same question — how much comes back if this wins — and they disagree only about what to measure it against.

American quotes against 100. A minus number is the stake required to win 100; a plus number is the profit on a stake of 100. So -150 means risk 150 to win 100, and +150 means risk 100 to win 150.

Decimal quotes the total return per unit staked, profit and stake together. 2.50 returns two and a half times the stake, so it is a profit of 1.50 per 1 risked. This is the format the arithmetic is easiest in, which is why almost every calculator on this site converts to it internally.

Fractional quotes profit against stake as a ratio. 3/2 wins three for every two risked. It is the traditional British notation and it survives in horse racing and futures markets.

Hong Kong is decimal minus one: profit per unit, ignoring the stake. Indonesian is American divided by 100. Malay is a signed number below 1 where positive means an underdog priced to return less than the stake as profit. They appear on Asian-facing books and on exchange aggregators, and they trip up bettors who assume any decimal-looking number is decimal odds.

Worked Example: The Standard -110

The most common price in American sports betting is -110, the two-way price on a spread or a total. Put it in and the whole row appears:

A 100 stake returns 190.91 in total, a profit of 90.91. And the number that actually matters is the last row: at -110 you have to win 52.38% of your bets to come out level, not 50%.

Converting By Hand

The conversions are short enough to do on paper, and worth knowing so a mispriced screen is obvious.

American to decimal. For a positive price, decimal = (odds ÷ 100) + 1. So +250 becomes 3.50. For a negative price, decimal = (100 ÷ |odds|) + 1. So -200 becomes 1.50.

Decimal to American. If decimal is 2.00 or higher, American = (decimal − 1) × 100. Below 2.00, American = −100 ÷ (decimal − 1).

Fractional to decimal. Divide the fraction and add one: 7/4 becomes 1.75 + 1 = 2.75.

Anything to probability. Probability = 1 ÷ decimal. That single step is the one to memorise, because every judgement about whether a bet is worth making runs through it.

Why The Probability Column Is The Useful One

Converting between notations is clerical. Converting to probability is analytical, because it turns a price into something you can disagree with.

-150 means nothing on its own. 60% is a claim: the market thinks this happens three times in five. You can hold a different view about 60%, and if your view is 66% you have found a bet. Comparing 60% to your own estimate is the entire job, and it is impossible to do while the price is still written as -150.

One caution: implied probabilities from a single price are always inflated, because the book's margin is baked in. Both sides of a -110 market imply 52.38%, and 52.38% twice adds up to 104.76%. Stripping that out is the vig calculator, and comparing your own number to the fair one is the expected value calculator.

If you want to see the process applied rather than described, every play on the membership card is published with the price, the projection behind it and the unit size, so the arithmetic on this page can be run against it.

Frequently Asked Questions