How to Add & Remove GST in Australia (10% Formula)
Australian GST is 10%. Whether you are quoting a client, checking a supplier invoice, or setting a retail price, you only need two formulas — and a free calculator when you want zero mistakes.
Skip the maths: free GST calculator Australia.
Formula 1: Add GST (exclusive → inclusive)
Inclusive price = Exclusive price × 1.10
GST amount = Exclusive price × 0.10
GST amount = Exclusive price × 0.10
Example: a $200 exclusive quote becomes $220 inclusive ($20 GST).
Formula 2: Remove GST (inclusive → exclusive)
Exclusive price = Inclusive price ÷ 1.10
GST amount = Inclusive − Exclusive
GST amount = Inclusive − Exclusive
Example: a $1,100 inclusive invoice is $1,000 exclusive + $100 GST. Do not multiply by 0.10 on an inclusive price — that overstates GST.
Remember: exclusive × 0.10 = GST; inclusive ÷ 11 = GST (same as inclusive − inclusive÷1.10).
Worked examples
| Exclusive | GST (10%) | Inclusive |
|---|---|---|
| $50.00 | $5.00 | $55.00 |
| $100.00 | $10.00 | $110.00 |
| $1,000.00 | $100.00 | $1,100.00 |
| $2,750.00 | $275.00 | $3,025.00 |
Common mistakes
- Taking 10% of an inclusive price (wrong — use ÷ 1.10).
- Forgetting GST-free items on mixed invoices.
- Rounding each line differently from your accounting software.