Formula for adding GST
Let’s start by calculating the GST component of a GST exclusive amount. To do this you simply multiply the value, excluding GST by 15% or by 0.15. To find the total including GST simply add the two values together.
In the example below B5 has been multiplied by 0.15, which is the same as 15%. You can type either value into the formula and Excel will give you the correct answer.
In cell B7 the GST exclusive amount held in B5 and the GST amount held in cell B6 have been added together to give the GST inclusive amount.
Formula for calculating the total including GST
There are times when you only want to calculate the Total figure including the GST. So let’s now have a look at calculating the total including GST.
This time we multiply the total by 115% or by 1.15.
In the example below cell B12, which is the figure without GST (exclusive figure) is being multiplied by 1.15 to calculate the Total including GST. The same result would have been found if you had used 115% instead of the 1.15.