How to convert betting fractions to decimals (& vice versa)
Converting betting fractions to decimals can be confusing.
In this post I’ll show you how to quickly convert fractional odds to decimal odds and vice versa.
The origins of fractional and decimal odds
Betting odds in the UK were traditionally expressed as fractions. Still in common use and originating from the on-course bookmakers, it wasn’t until the introduction of betting exchanges that decimal odds were introduced into the UK.
Decimal odds were the norm in Europe and Australia. UK sportsbooks adopted the format to appeal to the widened audience brought about by the explosion of the internet.
To those not familiar with the UK fractional odds, they could appear confusing. It was widely perceived that decimal odds were easier to understand.
Being able to quickly convert fractional odds to decimals and also in reverse, is of primary use when you are weighing up which are the best odds and across a range of bookmakers. Odds for the same bet may be expressed in a mixture of formats.
How to convert betting fractions to decimals
To convert betting fractions to decimals, you need to apply this simple formula to the fractional odds.
Divide the first number (the numerator) by the second number (the denominator) and add 1 = decimal odds.
Numerator / denominator +1 = decimal odds
For example, to convert fractional odds of 7/2 into decimal odds
7/2+1 = 4.5
How to convert decimal odds to betting fractions
Converting decimal odds to fractional odds is a slightly more complex calculation, but can be done following this 4 step process.
In this example, we’ll use decimal odds of 3.25. Take the decimal odds and minus 1
Then divide by 1
Multiply both the top and bottom number by multiples of 10 until the decimal point is removed from the top number and both the top and the bottom number are whole numbers.
In the case of our example
Simplify the fraction. To do this divide both the top and the bottom number by the same value until it reaches its lowest whole number.
The fractional odds of 3.25 are 9/4.
Another example using decimal odds Of 1.80
Step 1 – Decimal odds minus 1
1.80 – 1 = 0.80
Step 2 – Divide by 1
0.80 / 1
Step 3 – Remove the decimal point
Multiply the top and bottom number by 10. So, 0.80 X 10 = 8 and 1 X 10 = 10. Leaves a fraction of
8 / 10
Step 4 – Fraction down
Simplify the fraction, divide top and bottom number by 2. So, 8 / 2 = 4 and
10 / 2 = 5.
Fractional odds of 1.80 = 4 / 5
Note, you will find that not all decimal odds translate to fractional odds that are recognisable as ones regularly used traditionally in betting markets.
For example, decimal odds of 1.74 equates in its simplest form to fractional odds of 37/50.
This is down in one part to the tradition of the fractions that UK bookmakers originally used, and secondly because the expression of odds in decimals uses a fuller scale.
With the traditional UK fractional odds, bands in the odds were straddled. I.e. the next step up from 11/10 in fractional odds would traditionally be 6/5. Convert these fractional odds to decimals 2.10 and 2.20. All decimals in the range in between were not offered.
This was one-way bookmakers could build margin into their books and also to the less informed punters it was easy to disguise the books total overround and profit margin by speaking in a fractional odds language that was quite niche.
It’s fair to say that the general introduction of decimal odds into the UK betting markets has made the odds more understandable to the masses.
To make the whole process of cross calculation easier, I’ve added the conversion table below.
Betting fractions to decimals – odds conversion table (and vice versa)
As well as the fractional and equivalent decimal odds the third and sixth column in the table titled ‘percentage chance’ shows the implied probability for these odds.
If you want to read about how a ‘book’ is formed and bookmakers margins and overrounds then you can find it here.
|Fractional Odds||Decimal Odds||Percentage Chance||Fractional Odds||Decimal Odds||Percentage Chance|
Calculating returns from fractional odds
Some returns from betting fractions are relatively easy to calculate.
For example, £10 at odds of 5/1 is five times your initial stake £50, plus your £10 stake added, equals £60 returns.
Similarly £4 at 11/4, for every £4 you bet, you win £11 plus your initial stake returned equals a total of £15.
These relatively simple examples are referred to as ‘money to money’.
Where it becomes a little more complicated with the money to money calculations is where you have a stake amount that isn’t the same as, or easily divisible with the denominator number in the bet. For example a £13 bet at 11/4?
The calculation for working out returns on all fractional odds bets is…
Stake x numerator / denominator + stake = returns
For the example above £13 at 11/4
£13 X 11 / 4 + £13 = £48.5
Calculating returns from decimal odds
Calculating the returns from bets placed at decimal odds is far more straightforward.
Stake x odds = returns
For example, £13 at 3.75
£13 X 3.75 = £48.75