Odds Converter
Type odds in any format and get all four at once — American, decimal, fractional 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. American (+110 / −110) is what every US sportsbook quotes: a plus price is the profit on a $100 bet, and a minus price is the stake needed to win $100 — plus for underdogs, minus for favorites. Decimal (2.10) is the total return per dollar staked, including your stake back — it is what most books outside North America quote, 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. 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 favor. 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 sportsbook prices both sides so the percentages add up to more than 100%, and the excess is its margin — the vig. 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 −110 — the standard two-sided price on a spread or total — is 1.91 decimal, 10/11 fractional, and an implied probability of 110 ÷ 210 = 52.38%. A price of +110 is 2.10 decimal, 11/10, and 100 ÷ 210 = 47.62%. Two prices of −110 in the same market add to 104.76%, and that 4.76% is the sportsbook’s margin.
Odds are easy. Honest probabilities are hard.
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FAQ
What are American odds?
American (moneyline) odds are what US sportsbooks quote. A plus price is the profit on a $100 stake: +150 means a $100 bet wins $150. A minus price is the stake needed to win $100: -110 means you risk $110 to win $100. Plus prices are underdogs; minus prices are favorites.
How do I convert American odds to a probability?
For a minus price, divide the odds by the odds plus 100, ignoring the sign: -110 is 110 ÷ 210 = 0.5238, or 52.38%. For a plus price, divide 100 by the odds plus 100: +150 is 100 ÷ 250 = 0.40, or 40%. Note that this includes the sportsbook’s margin, so it overstates the true chance.
How do I convert American odds to decimal?
For a plus price, decimal = 1 + odds ÷ 100, so +150 is 2.50. For a minus price, decimal = 1 + 100 ÷ odds, ignoring the sign, so -110 is 1.91. Decimal odds show the total return per dollar staked, including the stake — the format most books outside North America use.
Why is even money +100 and not −100?
At exactly even money both American formulas give 100 and the sign is a convention: even money is quoted +100, which is 2.00 in decimal. It is a small thing that flips the sign on every coin-flip price if a converter gets it wrong.