Odds Converter
Type odds in any format and get all four at once — decimal, fractional, American and the implied probability behind them. Everything runs in your browser; nothing is stored.
The four formats, and who uses which
All four say the same thing in different words. Decimal (2.10) is the total return per dollar staked, including your stake back — it is what every Australian bookmaker quotes and it is the easiest to compare. Fractional (11/10) is the British convention and shows profit over stake, so your $1 back is implied rather than shown. American (+110 / −110) quotes profit on a $100 bet for underdogs and the stake needed to win $100 for favourites. Implied probability (47.62%) is the one that actually means something: how often the price says this has to win.
Why implied probability is the number that matters
Converting between formats is arithmetic. Converting to a probability is the step that lets you have an opinion. Once a price is a percentage you can compare it with your own estimate of how often the thing happens — and betting is just the business of finding places where those two numbers disagree in your favour. Everything else on this site is machinery for producing the second number honestly.
The catch: implied probability includes the margin
The percentage this tool shows is what the price implies, not what is true. A bookmaker prices both sides so the percentages add up to more than 100%, and the excess is their margin. Add up every outcome in a market and you will see it. To get the fair probability behind a price you have to take the margin out first — that is what the no-vig calculator does.
The formula
fractional n / d = (D − 1) as a fraction
American D ≥ 2 → +(D − 1) × 100
American D < 2 → −100 / (D − 1)
probability p = 1 / D
where D is decimal odds and p is the implied probability as a fraction.
Worked example
A price of 2.10 decimal is 11/10 fractional, +110 American, and an implied probability of 1 ÷ 2.10 = 47.62%. A price of 1.91 — the standard two-sided price — is 10/11, −110, and 52.36%. Two prices of 1.91 in the same market add to 104.71%, and that 4.71% is the bookmaker’s margin.
Odds are easy. Honest probabilities are hard.
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FAQ
What are decimal odds?
Decimal odds show the total return per dollar staked, including the stake. At 2.10, a winning $10 bet returns $21 — $10 back plus $11 profit. Australian bookmakers quote decimal, which is why it is the default here.
How do I convert odds to a probability?
Divide one by the decimal odds. At 2.50 the implied probability is 1 ÷ 2.50 = 0.40, or 40%. Note that this includes the bookmaker’s margin, so it overstates the true chance.
What does +110 or −110 mean?
American odds quote profit on a $100 stake for underdogs and the stake needed to win $100 for favourites. +110 means a $100 bet wins $110. −110 means you must stake $110 to win $100. In decimal those are 2.10 and 1.91.
Why does 2.00 convert to +100 and not −100?
At exactly evens both American formulas give 100 and the sign is a convention: evens is quoted +100. It is a small thing that flips the sign on every line-ball price if a converter gets it wrong.