Work backwards from a GST-included price to find the price before tax.
Divides the inclusive price back out to recover the pre-tax value.
Taxable value: Inclusive price × 100 ÷ (100 + rate)
When would I need to remove GST from a price?
This is common when a price already includes GST, and you need to know the price before tax — for accounting, or to check an invoice is correct.