Betting Odds Converter: American, Decimal & Fractional

A betting odds converter translates a price between American, decimal, and fractional formats, and shows the implied probability behind it. These are four ways of writing the exact same number, so once you can move between them you can compare any two sportsbooks no matter which format each one shows. Convert any price with the tool below, then read on for the formulas.

Try It: Odds Converter

Type a price into any field and the other three update live. It starts on +150, a common underdog line. Change it to see how the same bet looks in every format.

The implied probability field is the one that matters most. It turns a price into a percentage chance, which is the number you actually need to judge whether a bet is worth making. More on that below.

The Four Ways to Show a Price

Every sportsbook quotes the same underlying number in one of these formats. Which one you see depends mostly on where the book operates.

• American odds are the default in the United States. A positive number (+150) is how much profit you win on a $100 stake. A negative number (−200) is how much you must stake to win $100. Even money is +100.
• Decimal odds dominate in Europe, Australia, and Canada. The number is your total return per $1 staked, profit plus your stake back. Decimal 2.50 means $2.50 back for every $1, so $1.50 profit. Even money is 2.00.
• Fractional odds are traditional in the United Kingdom and Ireland. The fraction is profit over stake. 3/2 means $3 profit for every $2 staked. Even money is 1/1, often written "Evens".
• Implied probability is the format that is not really a format. It is the price rewritten as a percentage: the win rate the bet needs to break even. +150 implies a 40% chance.

A price of +150 equals 2.50 in decimal, 3/2 in fractional, and a 40% implied probability. Same bet, four notations. Line up two books that quote differently and you cannot tell which is offering the better price until you convert them to a shared format.

Odds Conversion Formulas

You do not need these to use the converter, but knowing them makes odds stop feeling arbitrary.

American to decimal. Split by sign:

$\text{Decimal} = \frac{\text{American}}{100} + 1 \quad (\text{positive odds})$

$\text{Decimal} = \frac{100}{\lvert \text{American} \rvert} + 1 \quad (\text{negative odds})$

So +150 becomes 150 / 100 + 1 = 2.50, and −200 becomes 100 / 200 + 1 = 1.50.

Decimal to American. Split at 2.00 (even money):

$\text{American} = (\text{Decimal} - 1) \times 100 \quad (\text{decimal} \geq 2.00)$

$\text{American} = \frac{-100}{\text{Decimal} - 1} \quad (\text{decimal} < 2.00)$

Fractional to decimal. Divide the fraction and add 1:

$\text{Decimal} = \frac{\text{Numerator}}{\text{Denominator}} + 1$

So 3/2 becomes 3 / 2 + 1 = 2.50.

Decimal to implied probability. The cleanest formula of the set, and the reason decimal is the format worth thinking in:

$\text{Implied Probability} = \frac{1}{\text{Decimal}} \times 100\%$

Decimal 2.50 gives 1 / 2.50 = 40%.

Quick Reference: Common Odds Conversions

A chart for the lines you see most often. Positive American odds are underdogs; negative are favorites.

American	Decimal	Fractional	Implied probability
+300	4.00	3/1	25.0%
+200	3.00	2/1	33.3%
+150	2.50	3/2	40.0%
+100	2.00	1/1	50.0%
−110	1.91	10/11	52.4%
−150	1.67	2/3	60.0%
−200	1.50	1/2	66.7%
−300	1.33	1/3	75.0%

The −110 row is worth memorizing. It is the standard price on a point spread or total, and its 52.4% implied probability (rather than a clean 50%) is your first glimpse of the vig, the margin the book charges on a balanced market.

Why Implied Probability Is the Number That Matters

Converting formats is the easy half. The reason to bother is implied probability, because it is the only format you can reason about.

A price is good or bad only relative to the real chance of the outcome. If you think a team wins 45% of the time and the book prices it at +150 (40% implied), you are getting paid as if the event is less likely than you believe it is. That gap is your edge.

There is a catch the −110 row already hinted at. The implied probabilities a book posts always add up to more than 100%, and that extra slice is the vig. To find the true, fair probability you have to strip the vig back out. That is what a no vig calculator does, and the full method for every market lives in the De-Vig Playbook. Once you have the fair probability, comparing it against real prices to find bets that pay more than they should is the whole idea behind positive expected value betting.

Sports betting is not risk free and no outcome is guaranteed. Converting odds and reading implied probability tells you whether a price is fair, not whether a bet will win. Any individual bet can still lose.

Converting Prediction Market Prices

Prediction markets like Kalshi and Polymarket do not quote American or decimal odds at all. They quote a price in cents that already is the probability: a contract trading at 40 cents implies a 40% chance and pays out at $1. That maps straight onto the implied-probability column above, which makes these markets easy to line up against a sportsbook.

To turn a Kalshi or Polymarket price into American or decimal odds, use the prediction market converter, or read the walkthroughs for the Kalshi odds converter and the Polymarket odds converter.

Frequently Asked Questions

What is a betting odds converter?

A betting odds converter is a tool that translates a price between American, decimal, and fractional formats and shows the implied probability behind it. You enter odds in any one format and it instantly returns the same price in the other three, so you can compare books that quote differently.

How do you convert American odds to decimal?

For positive American odds, divide by 100 and add 1, so +150 becomes 150 / 100 + 1 = 2.50. For negative American odds, divide 100 by the absolute value and add 1, so −200 becomes 100 / 200 + 1 = 1.50. Even money, +100, is exactly 2.00 in decimal.

What does −110 mean?

−110 is American odds meaning you stake $110 to win $100, the standard price on a point spread or total. In decimal it is 1.91, in fractional it is 10/11, and its implied probability is 52.4%. The reason it is not a clean 50% is the vig, the book's built-in margin.

Which odds format is best?

No format is more accurate; they all describe the same price. Decimal is the easiest to calculate with because its implied probability is simply one divided by the number. American is standard at United States sportsbooks, and fractional is traditional in the United Kingdom. A converter lets you work in whichever you prefer.

How do you convert odds to implied probability?

Convert the odds to decimal, then take one divided by the decimal figure and multiply by 100. Decimal 2.50 gives 1 / 2.50 = 40%. Implied probability is the break-even win rate a price bakes in, which is the number you compare against your own estimate to spot value.

Convert Any Price Instantly

Converting one price by hand is quick. Converting every line across every book, fast enough to act before the number moves, is not. That is what the tool is for.

Drop any American, decimal, or fractional price into the Odds Converter and it returns all four formats at once, including the implied probability you need before you can measure value. Open the Odds Converter and stop doing the arithmetic in your head.