FORMWISE GUIDE
How to Calculate GST on a Price
A plain-language explanation of the arithmetic behind adding and extracting GST. Tax treatment depends on the actual transaction and applicable rules.
Adding GST
GST amount = pre-tax price × GST rate ÷ 100. Add the GST amount to the pre-tax price for the mathematical inclusive amount.
Removing GST
For a purely mathematical inclusive-price calculation, divide the inclusive amount by 1 + rate/100 to obtain the pre-tax amount.
Verify tax treatment
Use the FormWise calculator for arithmetic, but verify applicable GST rules with authoritative sources or a qualified tax professional.