GST Explained: Adding vs Removing Tax

To add GST, multiply the base amount by the rate: 10,000 at 18% adds 1,800 for a gross of 11,800.

To remove GST from an inclusive price, divide rather than subtract: 11,800 ÷ 1.18 = 10,000. Subtracting 18% of the gross would wrongly give 9,676.

Invoices must show the base, the tax and the total separately, so getting the direction of the calculation right matters for compliance as much as arithmetic.