Fractional odds

Fractional odds are the odds traditionally favoured by British and Irish bookmakers. They are written in fraction form with a slash (/) or hyphen (-), and show the ratio of returns to stake.

Fractional odds consist of a numerator - the first number - and a denominator - the second number.

Fractional odds present the profit the bettor makes per stake placed. The numerator demonstrates the returns and the denominator shows the stake.

For example, odds of 5/2 would see returns of £5 for every £2 stake placed.

How to read fractional odds

Outcomes with fractional odds of over 1/1 - where the first number is bigger than the second - are considered underdogs, meaning the outcome is regarded by the bookmaker as less likely to happen.

Outcomes with fractional odds under 1/1 - where the first number is smaller than the second - are considered favourites, meaning the outcome is regarded by the bookmaker as more likely to happen than not.

Fractional odds of 1/1 are also referred to as evens, meaning the bookmaker is suggesting that the outcome has a 50/50 chance of happening.

Calculating returns using fractional odds

To calculate returns using fractional odds, the following formula is used:

Stake * (numerator / denominator)

For example

5 * (3 / 1) = 15

Therefore returns would be £15

Converting fractional odds into decimal odds

To convert fractional odds into decimal odds, the following formula is used:

(numerator / denominator) + 1

For example

(5 / 6) + 1 = 1.83

Converting decimal odds into fractional odds

There is no formula to convert decimal odds into fractional odds, just a little bit of maths to do instead.

Step 1) Convert decimal odds into fraction form by subtracting 1 from the decimal

Step 2) This number becomes the numerator (the first number), and use the number 1 as the denominator (the second number)

Step 3) Convert the fraction into its simplest form by finding the nearest whole number that the numerator divides into.

Step 4) The number by which you times the numerator by to make it into a whole number becomes the denominator.

For example

  • Atalanta vs Roma - over 2.5 goals at odds of 3.40

Step 1) 3.40 - 1 = 2.40

Step 2) 2.4/1

Step 3) 2.4 * 5 = 12

Step 4) 5/12

Converting fractional odds into American odds

Fractional odds above 1/1 will provide positive American odds. To convert fractional odds of above 1/1 into American odds, the following formula is used:

(numerator / denominator) *100

For example

(7 / 4) * 100 = +175

Fractional odds of under 1/1 will provide negative American odds. To convert fractional odds under 1/1 into American odds, the following formula is used:

-100 / (numerator / denominator)

For example

  • Juventus vs Roma - Juventus to win at odds of 1/4

-100 / (1 / 4) = -400

Converting American odds into fractional odds

In order to convert American odds into fractional odds, the odds are arranged in a certain way and then reduced to their simplest form.

For positive odds, to convert American odds into fractional odds, the odds are arranged as follows:

Odds/100

And then reduced into simplest form.

For example

  • Barcelona vs Real Madrid - Real Madrid to win at odds of +300

300/100 reduces down into 3/1

For negative odds, to convert American odds into fractional odds, the odds are arranged as follows:

100/odds

And then reduced into simplest form.

For example

  • Atletico Madrid vs Valencia - Atletico Madrid to win at odds of -250

100/250 reduces down to 2/5

Converting fractional odds into implied probability

Implied probability is the conversion of odds into a percentage to show the expected probability of an outcome.

The formula to convert fractional odds into implied probability is as follows:

denominator / (denominator + numerator) * 100

For example

  • Manchester United vs Chelsea - Manchester United to win at odds of 1/2

(1 / (1+2)) * 100 = 66.7%

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