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.

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, and the format of every moneyline bet you see there. 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, usually 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.

Here is why that matters. Say one book offers a team at +150 and another quotes the same team at decimal 2.45. Convert 2.45 and it is +145 (40.82% implied), so the +150 pays $5 more profit on every winning $100 stake. You cannot see that until both prices share a format, and taking the better one every time is the habit called line shopping.

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. The full American to decimal chart, with every common line, is in American odds to decimal.

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%. The implied probability calculator guide goes deeper on this one formula.

Quick Reference: Common Odds Conversions

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

The decimal column is rounded to two places. The fractions are exact, which is why −110 is 10/11 and not the 91/100 that a rounded 1.91 would suggest.

The −110 row is worth memorizing. It is the standard price on a point spread or total. 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. As an illustration, if you think a team wins 45% of the time and the book prices it at +150 (40% implied), the book is paying as if the event is less likely than you believe. That gap is the edge you think you have, and it is only as good as your 45% estimate.

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. How sportsbooks make money breaks down where it comes from.

To find the true, fair probability you have to strip the vig back out. That is what a no vig calculator does, no vig fair odds explains what the result means, 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. The expected value calculator guide runs that comparison one bet at a time.

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.

Odds Formats Inside SmartStake

You only need the converter for prices you find outside SmartStake. Inside the app, one account setting picks the format every tool shows: American (the default), decimal, or percent, which is implied probability.

The setting lives in Display and behavior and applies to bet cards, the Arbitrage Finder, the Bet Tracker, and the Odds Screen. Change it once and every price across every book reads in the same format. Fractional is not one of the in-app formats, so use the converter above when you want a price as a fraction.

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 $1 if it wins, before any exchange fee.

That maps straight onto the implied probability column above, which makes these markets easy to line up against a sportsbook. Prediction market betting explains how event contracts work.

To turn a Kalshi or Polymarket price into American or decimal odds, use the prediction market converter. The walkthroughs for the Kalshi odds converter and the Polymarket odds converter cover each exchange's fees.

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.