Calculator
Enter odds
Fractional odds should be entered like 5/2.
How to use this tool
Enter the requested figures, press the calculate button and review the result. The explanation below shows what each output means.
Enter a price in American, decimal or fractional format and instantly see it converted to the other two formats, along with the implied probability. The sections below explain how each format works and why converting between them matters for serious bettors.
Why three different odds formats exist
American, decimal and fractional odds all express exactly the same underlying information, the price being offered on a bet, but evolved in different regions and remain the convention in different markets today: American odds dominate in the United States, decimal odds are standard across most of Europe, Australia and exchanges, and fractional odds remain traditional in UK horse racing and some bookmakers.
Because different sportsbooks and regions default to different formats, being comfortable converting between all three is a practical necessity for any bettor comparing prices across multiple platforms.
How American odds work
American odds use a plus or minus sign: a negative number shows how much must be staked to win 100 units, while a positive number shows how much is won on a 100-unit stake. A -150 favourite requires risking 150 to win 100, while a +130 underdog wins 130 on a 100 stake.
This format can feel unintuitive at first specifically because favourites and underdogs are expressed with different signs and different reference points, unlike decimal odds where every price uses the same consistent calculation regardless of favourite or underdog status.
How decimal odds work
Decimal odds express the total return, including the original stake, for every one unit staked. A decimal price of 2.50 means a 100 stake returns 250 total if the bet wins, made up of 150 profit plus the original 100 stake returned.
Decimal odds are generally considered the most straightforward format for calculation purposes, since multiplying stake by decimal odds directly gives total return with no additional steps, which is why they are the standard format across most quantitative betting models and exchanges.
How fractional odds work
Fractional odds express profit relative to stake as a fraction, such as 6/4, meaning a 4-unit stake profits 6 units if the bet wins, on top of the original stake being returned. This format has deep historical roots in UK horse racing and remains common in some traditional bookmaking contexts today.
Fractional odds can be less intuitive for quick mental calculation than decimal odds, particularly for prices that do not reduce to simple, familiar fractions, which is part of why decimal odds have become increasingly dominant even in markets where fractional odds were traditionally the default.
Implied probability across all three formats
Regardless of which format a price is expressed in, it always implies the same underlying probability once converted using the appropriate formula for that specific format, covered in more depth in the implied probability guide on the main Betting Academy.
This calculator shows implied probability directly alongside the converted odds, letting you see at a glance not just what a price looks like in another format, but what probability of winning that price actually represents before any margin is removed.
Worked conversion example
Consider a price of -150 in American odds. Converting this to decimal odds produces approximately 1.67, meaning a 100 stake returns 167 total if the bet wins. Converting the same price to fractional odds produces approximately 2/3, reflecting the same underlying value expressed in yet another format.
The implied probability for this specific price works out to approximately 60%, before removing any sportsbook margin, illustrating how all three formats and the implied probability all describe exactly the same underlying price from different angles.
Why format familiarity matters for price shopping
When comparing the same bet across multiple sportsbooks that use different default odds formats, quickly converting every price into a single common format is essential for making a genuine apples-to-apples comparison, since it is easy to misjudge which of two differently formatted prices is actually better without converting them first.
This is particularly relevant for bettors who use exchanges, which almost universally default to decimal odds, alongside traditional sportsbooks that may default to American or fractional formats depending on region.
Rounding and precision considerations
Converting between formats occasionally introduces small rounding differences, particularly for fractional odds which do not always convert to clean, simple fractions, worth being aware of when comparing very tight price differences across formats, since a rounded conversion might obscure a genuinely meaningful but small difference in the underlying price.
For most practical purposes this rounding is immaterial, but bettors doing precise, quantitative price comparison across a large number of bets should be aware that some minor precision loss can occur, particularly when going through fractional odds.
Common mistakes when converting odds
A frequent error is misreading the sign on American odds, confusing a favourite's negative price with an underdog's positive price, particularly when working quickly across multiple games and formats simultaneously.
A second common mistake is forgetting that decimal odds include the returned stake in the total figure shown, sometimes leading to confusion when comparing a decimal odds return figure against an American odds profit figure, which represents only the profit rather than the total return.
Using this calculator for price shopping
A practical habit is converting every sportsbook's price for a specific bet into the same single format, most commonly decimal odds given its straightforward calculation properties, before comparing them side by side, removing any risk of format-related confusion when judging which specific price actually offers better value.
Building this conversion habit into a regular price-shopping routine, covered in more depth throughout this site's Trading Academy, is a small but genuinely valuable practice for any bettor who regularly compares prices across multiple sportsbooks using different default formats.
Odds conversion and mobile betting
Many bettors now compare prices across sportsbooks using mobile apps that may default to different odds formats depending on region and platform settings, making quick, reliable conversion skills, or a tool like this one, increasingly practical for real-time price shopping on the go.
A closing note on building fluency
With enough practice, converting between formats becomes close to automatic for common price ranges; until that fluency develops, keeping this calculator readily accessible during active price shopping is a practical, low-effort habit.
Odds conversion in live, in-play markets
Live betting odds update rapidly during an event, and having quick access to format conversion becomes especially valuable when comparing a live price against multiple sportsbooks that may display different formats by default during fast-moving in-play situations.
The same price in three formats
The table below shows one example price expressed in all three common odds formats, alongside its implied probability.
| American | -150 |
| Decimal | 1.67 |
| Fractional | 2/3 |
| Implied probability | Approximately 60% |
All four figures in this table describe exactly the same underlying price; converting between them changes only the presentation, not the actual value being offered.
Key takeaways
- American, decimal and fractional odds all express the same underlying price in different regional conventions.
- Decimal odds are generally the most straightforward format for direct calculation purposes.
- Every price format implies the same underlying probability once converted using the correct formula.
- Converting all prices to a single common format before comparing is essential for accurate price shopping.
- Small rounding differences can occur when converting through fractional odds, worth noting for precise comparisons.
Frequently asked questions
Does this calculator guarantee a profit?
No. It performs the stated conversion but cannot remove model error, price movement, limits or settlement risk.
Which format should I use for calculations?
Decimal odds are generally the most straightforward for direct calculation, since multiplying stake by decimal odds gives total return directly.
Does the tool store my information?
No. Calculations run locally in your browser and are not saved by the calculator.
Why do American odds use plus and minus signs?
Favourites and underdogs are expressed from different reference points, showing either the stake needed to win 100 or the profit from a 100 stake.
Can converting odds introduce rounding errors?
Occasionally with fractional odds specifically, since not every price reduces to a clean, simple fraction, though this is rarely material for practical purposes.