Master Odds Converter

Betting odds exist in three formats: Decimal (Europe/Australia), American/Moneyline (USA), and Fractional (UK/Ireland). All three express the same underlying probability — they simply present it differently. A professional bettor must be fluent in all three because the same event may be quoted in different formats across different bookmakers. The sections below break down how to read each format, when you'll encounter it, and how to convert between all three by hand.

Decimal odds are the default in Europe, Australia, Canada, and among professional bettors and betting exchanges like Betfair. A decimal odd of 2.50 means you receive $2.50 total for every $1 wagered — your $1 stake back plus $1.50 profit. Even money is exactly 2.00. A heavy favorite might sit at 1.20 (20% profit); a longshot might be 8.00 (700% profit).

Implied probability is the simplest of the three formats to compute: p = 1 / decimal. Decimal 1.50 → 66.67% implied probability. Decimal 4.00 → 25%. Anything below 2.00 means the bookmaker rates the outcome more likely than not to happen. Because decimal odds convert to probability and to total return in one step, they are the format used internally by virtually every professional betting model — including the calculator above.

American odds are the standard at US sportsbooks. A positive number like +130 shows how much profit a $100 bet returns. A negative number like −150 shows how much you must stake to win $100 profit. Every even-money price is written as +100 (equivalent to −100 and to decimal 2.00).

To convert to decimal: positive American → (American / 100) + 1; negative American → (100 / |American|) + 1. So −150 becomes (100/150) + 1 = 1.667, equivalent to fractional 2/3. The standard US spread and totals price is −110 — decimal 1.909, implied probability 52.38%. Because both sides of a spread are usually −110, the book totals 104.76%, a 4.76% theoretical hold for the sportsbook.

Fractional odds (e.g., 5/2, read "five-to-two") are the traditional format in UK and Irish horse racing and bookmaking. They express net profit relative to stake: 5/2 means you profit $5 for every $2 staked, a total return of $7 on a $2 bet. A fraction with a smaller numerator than denominator, like 1/4, describes an odds-on favorite — profit smaller than stake.

To convert fractional odds to decimal: decimal = (numerator / denominator) + 1. So 5/2 → 3.50, 7/4 → 2.75, and 1/4 → 1.25. Implied probability from a fraction is denominator / (numerator + denominator): for 5/2 that's 2/(5+2) = 28.57%. Fractional notation can be ambiguous — 5/2 and 10/4 describe the identical price, but a book may quote either depending on convention, which is one more reason decimal is easier to work with at scale.

Which format you see is almost entirely a function of geography, not of the underlying odds. European, Australian, and Canadian books default to decimal. US sportsbooks default to American/moneyline. UK and Irish bookmakers — especially in horse racing — still favor fractional, though most now also show decimal on request.

For calculation, the answer is unambiguous: use decimal. Expected value, Kelly stake sizing, and no-vig fair-odds math are all one-step operations in decimal; American requires branching on sign, and fractional requires an extra division. Serious bettors typically think and calculate in decimal even when the sportsbook displays American or fractional, converting only at the point of placing the bet.