The formula for calculating GST in New Zealand has changed since the rise in GST, however it is still relatively straight forward.

Before we start, we should understand that all GST calculation is relative to the "base" which is the original figure that you have. If you are wanting to add GST, then the base would be the price without GST alternatively if you are looking at finding the GST content of a figure, then the base is the GST inclusive figure. For the example below, the base will always be \$100 to keep things simple.

In the example you see below, we have started with a base figure of \$100. Given that the rate of GST that we are using is 15% (which is written as 0.15 as a decimal) we can see that in this example we have the base (\$100) and to that we have to add the GST of the original amount which in this case is (15% of \$100). From that point, all we have to do is add the new found GST content (\$15) to the base figure (\$100) to get the new GST inclusive figure of \$115.

Finding GST Content

In the example below, we can see that this calculation is slightly harder, but using the formula can be found quite easily. The base in this example is \$100 again. Firstly we can see that overall the formula is GST Content =((BASE*3)/23) which on \$100 is \$13.04.