Odds Converter

The Compare.bet odds converter lets you convert fractional, decimal and American odds instantly – it even tells you the implied probability! Try it out below.


Different types of odds explained

Let’s take a closer look at the differences between each odds type.


Fractional odds are traditionally most common at betting sites in Ireland, but you’ll find them at Ireland’s newest bookies too. With fractional odds, the numerator tells you how much you’ll win when you place a bet equal to the value of the denominator. The numerator reflects the net profit, so a €10 bet with odds 2/1 will see you win €20 profit.


Decimal odds now rival fractional odds as the most popular format and are the default format in most of Europe, Australia and Canada because of their simplicity. To calculate your potential winnings, you simply multiply your stake by the decimal odds.

The decimal odds reflect your total returns, meaning both your profit and original stake. So if you win a €10 bet with 2.5 odds, you’ll get €25 back – your €10 stake plus €15 profit.


As the name suggests, these odds are used at US sportsbooks. With American odds, positive odds tell you how much you’ll win from placing a €100 wager, while negative odds show you how much you need to wager to win €100. 

American odds reflect your net profit, so a €10 bet on +130 odds would net you €23 – €13 profit. A €10 bet on -160 odds would win you €6.25 profit.

How it works

The maths behind the odds converter

Odds conversion calculations vary depending on the odds formats in question. Luckily, our odds converter does the hard work for you, so you don’t need to get your calculator out. However, if you’re interested in how the odds converter works, here’s a look at the maths behind it.

Fractional and decimal odds

To convert fractional odds to decimal odds, you need to turn the fraction into decimal form and then add 1. To convert a fraction to a decimal, you simply divide the numerator (the number left of the divider) by the denominator (the number right of the divider).

Let’s say you want to convert fractional odds of 1/5 into decimal format. To do this, you’d do the following calculations:

1/5 = 0.2

0.2 + 1 = 1.2

To convert decimal odds to fractional odds, you need to do the reverse. This means positioning the decimal number as the numerator and 1 as the denominator. You then multiply the top and bottom numbers by ten until there are no decimal places left.

For example, to convert odds of 1.4, you do the following:

1.4 – 1 = 0.4

(0.4/1) x 10 = 4/10

You then simplify the fraction by dividing both numbers by the largest common denominator. In this case, the largest common denominator is 2, so the fractional odds you’re left with are 2/5.

Fractional and American

The calculation for converting fractional odds to US odds differs depending on whether you’re converting odds over 1/1 (an underdog) or under 1/1 (a favourite). However, you’ll always need to convert the fraction into a decimal, dividing the numerator by the denominator.

For odds over 1/1, you then multiply the fraction by 100. So to convert odds 3/2, you’d carry out the following calculation:

3/2 = 1.5

1.5 x 100 = +160

If you want to convert odds on a favourite, such as 2/3, you first convert the fraction to a decimal and then divide -100 by the decimal. The calculation for this is:

2/3 = 0.67

-100/0.67 = -150

So here you would divide -100 by 0.67 to give you -150.

Converting American odds to fractional odds requires the reverse calculations. For positive odds, this means multiplying the odds by 100, converting the answer to a fraction and then reducing the fraction to its simplest form. To convert negative US odds, you divide 100 by the odds, turn the decimal into a fraction and then reduce to its simplest form.

Decimal and American

The calculation for decimal to American odds also depends on whether you’re converting odds on an underdog or favourite. For decimal odds of 2.00 or greater, you simply minus 1 and multiply by 100. So for decimal odds of 3.00, you do this:

3 – 1 = 2

2 x 100 = +200

To convert odds of less than 2.00, you minus 1 from the decimal and then times the answer by -100. So the calculation for decimal odds of 1.50 is:

1.50 – 1 = 0.5

0.5 x -100 = -200

To convert American odds to decimals, you simply carry out the reverse calculations. So for positive odds, you divide by 100 and plus 1, and for negative US odds, you disregard the negative sign, divide by 100 and then add 1. 

Implied probability

Betting sites don’t tend to display the implied probability of bets, but it is very useful for bettors to understand. The implied probability provides the simplest reflection of how likely a bookie believes a particular event is to happen. For example, an implied probability of 10% shows that a bookie believes there is around a 1 in 10 chance of that event occurring. 

The calculation for converting odds to a percentage depends on the odds format. For fractional odds you use the following equation:

(Denominator / (denominator + numerator)) x 100 = implied probability 

For decimal odds, the calculation is:

(1/decimal odds) x 100 = implied probability

And finally, to work out the implied probability from US odds you do the following:

(Negative odds / (negative odds + 100)) x 100 = implied probability 

(100 / (positive odds + 100)) x 100 = implied probability

Examples table

Browse some common conversions between different odds types

Here are a few examples of converted odds to see how different formats compare. 

Fractional Decimal American Implied Probability
1/5 1.20 -500 83.3%
2/9 1.22 -450 81.8%
1/4 1.25 -400 80%
2/7 1.29 -350 77.8%
3/10 1.30 -333.3 76.9%
1/3 1.33 -300 75%
4/11 1.36 -275 73.3%
4/9 1.44 -225 69.2%
1/3 1.33 -300 75%
5/4 2.25 125 44.4%
11/8 2.38 137.5 42.1%
9/1 10.00 900 10%
10/1 11.00 1000 9.1%
20/1 21.00 2000 4.8%
50/1 51.00 5000 2%
100/1 101.00 10000 1%

The people behind this page

Compare.bet's online gambling content experts helped write, edit and check the content on this page:

Noel is a writer for Compare.bet with over a decade of experience writing on topics including online casino and sports betting.