Betting Odds Formats: American, Decimal, and Fractional Explained

Date: 27.10.2025

Betting Guide

All betting odds formats: American, Decimal, and Fractional, express the same two fundamental pieces of information: the potential payout relative to your stake and the implied probability of the event occurring. They are simply different ways of writing the same number.

For example, odds quoted as $\mathbf{3/2}$ (Fractional) are equivalent to $\mathbf{2.50}$ (Decimal) and $\mathbf{+150}$ (American). All three mean a $\$100$ bet will result in $\$150$ profit (a total return of $\$250$ ) and imply a $\mathbf{40\%}$ chance of winning.

Understanding how to read and convert these formats is essential for any bettor who shops for lines or uses international sources.

American Odds (Moneyline) 🇺🇸

American odds are the standard format in the United States and are expressed as a number with a plus ( $\mathbf{+}$ ) or minus ( $\mathbf{-}$ ) sign. This format is centered around a $\$100$ baseline.

How to Read American Odds

Positive Odds ( $\mathbf{+}$ ): These indicate the underdog and show the net profit you would earn on a $\mathbf{\$100}$ stake.

Example: $\mathbf{+150}$ means a $\$100$ bet wins $\mathbf{\$150}$ profit (total payout $\$250$ ).
A higher positive number indicates a bigger underdog and a larger potential profit.

Negative Odds ( $\mathbf{-}$ ): These indicate the favorite and show the amount you must bet to profit $\mathbf{\$100}$ .

Example: $\mathbf{-150}$ means you must wager $\mathbf{\$150}$ to win $\mathbf{\$100}$ profit (total payout $\$250$ ).
A larger negative number (e.g., $-300$ , $-500$ ) indicates a bigger favorite, requiring a larger stake for the same $\$100$ profit.

Note: For both positive and negative odds, your original stake is always returned in a winning bet. Even odds (a $50/50$ chance) are commonly expressed as $\mathbf{+100}$ , though due to the bookmaker’s vig, you often see both sides listed at $\mathbf{-110}$ .

Decimal Odds (European Odds) 🌍

Decimal odds are used widely across Europe, Canada, Australia, and many other international markets. This format is often favored for its simplicity in calculating payouts and implied probability.

How to Read Decimal Odds

A decimal odd represents the total amount returned for every $\mathbf{\$1}$ staked, which includes your original stake. It is a straightforward payout multiplier.

Example: Decimal odds of $\mathbf{2.50}$ mean that for every $\$1$ bet, the total return is $\$2.50$ .

Profit is the decimal number minus $\mathbf{1}$ (to remove the stake): $\$2.50 - \$1.00 = \mathbf{\$1.50}$ profit per $\$1$ staked.

Calculating Payout: Simply multiply your stake by the decimal odd.

Formula: $\text{Total Payout} = \text{Stake} \times \text{Decimal Odds}$ .
A $\$50$ wager at $\mathbf{3.00}$ odds yields $\mathbf{\$150}$ total payout $(\$50 \times 3.00)$ , meaning $\$100$ profit.
Even money odds are $\mathbf{2.00}$ . Faves are below $2.00$ (e.g., $1.50$ ), and underdogs are above $2.00$ (e.g., $4.00$ ).

Decimal odds are highly convenient for calculating parlays: you just multiply the decimal odds of all legs to get the overall parlay odd.

Fractional Odds (British Odds) 🇬🇧

Fractional odds are the oldest format, traditionally used in the United Kingdom and Ireland, particularly for horse racing. They are written as a ratio, such as $\mathbf{X/Y}$ .

How to Read Fractional Odds

Fractional odds quote the net profit relative to the stake.

Interpretation: An odd of $\mathbf{X/Y}$ means “you win X units of profit for every Y units staked.” You get your stake back in addition to the profit.

Example: $\mathbf{5/1}$ (read “five-to-one”) means you win $\$5$ profit for every $\$1$ wagered. A $\$10$ bet at $5/1$ profits $\mathbf{\$50}$ (total return $\$60$ ).
Example: $\mathbf{1/2}$ (read “one-to-two,” an odds-on favorite) means you must bet $\$2$ to win $\$1$ profit. A $\$20$ bet profits $\mathbf{\$10}$ (total return $\$30$ ).

Even Money: $\mathbf{1/1}$ is called “evens” and means you double your money (e.g., a $\$10$ bet wins $\$10$ profit).

Calculating Payout:

Formula: $\text{Profit} = \text{Stake} \times (\mathbf{X} \div \mathbf{Y})$ .
A $\$40$ bet at $\mathbf{3/2}$ odds yields a profit of $\$40 \times (3 \div 2) = \mathbf{\$60}$ (total return $\$100$ ).

Conversion Formulas and Implied Probability

Being able to convert between formats is key to finding the best value. Converting odds to Implied Probability is the easiest way to compare different lines.

Key Conversion Formulas

To Convert	Formula	Example
Fractional ( $X/Y$ ) to Decimal	$(X \div Y) + 1$	$3/2 \implies (3 \div 2) + 1 = \mathbf{2.50}$
Decimal (D) to American (+)	$(D - 1) \times 100$	$2.50 \implies (2.50 - 1) \times 100 = \mathbf{+150}$
Decimal (D) to American (-)	$-100 \div (D - 1)$	$1.50 \implies -100 \div (1.50 - 1) = \mathbf{-200}$
American ( $+X$ ) to Decimal	$(X \div 100) + 1$	$+150 \implies (150 \div 100) + 1 = \mathbf{2.50}$
American ( $-Y$ ) to Decimal	$(100 \div Y) + 1$	$-200 \implies (100 \div 200) + 1 = \mathbf{1.50}$

Implied Probability

Implied probability is the chance of winning (in percentage form) that the odds represent.

Decimal (D): $\text{Implied Probability} = (1 \div D) \times 100\%$

Example: Decimal $\mathbf{2.50} \implies (1 \div 2.50) = 0.40 \implies \mathbf{40\%}$

Fractional ( $\mathbf{X/Y}$ ): $\text{Implied Probability} = \mathbf{Y} \div (\mathbf{X} + \mathbf{Y}) \times 100\%$

Example: Fractional $\mathbf{3/2} \implies 2 \div (3+2) = 0.40 \implies \mathbf{40\%}$

American ( $\mathbf{+X}$ ): $\text{Implied Probability} = 100 \div (X + 100) \times 100\%$

Example: American $\mathbf{+150} \implies 100 \div (150 + 100) = 0.40 \implies \mathbf{40\%}$

American ( $\mathbf{-Y}$ ): $\text{Implied Probability} = Y \div (Y + 100) \times 100\%$

Example: American $\mathbf{-200} \implies 200 \div (200 + 100) \approx 0.667 \implies \mathbf{66.7\%}$

Fractional	Decimal	American	Implied Probability
$\mathbf{1/5}$	$1.20$	$\mathbf{-500}$	$83.3\%$
$\mathbf{1/1}$ (Evens)	$2.00$	$\mathbf{+100}$	$50.0\%$
$\mathbf{2/1}$	$3.00$	$\mathbf{+200}$	$33.3\%$
$\mathbf{5/1}$	$6.00$	$\mathbf{+500}$	$16.7\%$

Pros and Cons of Each Format

Format	Pros	Cons
Decimal	Easiest for payout and parlay calculations. Simplest conversion to implied probability ( $1 \div D$ ). Most used internationally.	Includes stake in the number (can confuse new bettors). Unfamiliar to US/UK bettors by tradition.
Fractional	Culturally traditional in the UK/Ireland. Clearly expresses profit:stake ratio. Used widely for horse racing.	Confusing for newcomers. Requires remembering to add the stake back for total return. Harder to use for quick calculations of non-standard fractions.
American	Instantly identifies favorites ( $\mathbf{-}$ ) vs. underdogs ( $\mathbf{+}$ ). Tied to the familiar $\$100$ betting baseline in the US.	Dual-scale system (positive/negative) can be unintuitive. Requires different formulas for calculating probability for favorites and underdogs.

Today, most online sportsbooks allow you to select your preferred format, making the choice a matter of personal preference and regional convention.

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