Calculators guide
How to Calculate GST: Add It, Remove It, and Common Mistakes
Updated 27 September 2026 · 3 min read
Whether you are a sole trader writing an invoice, a shopper checking a receipt or a bookkeeper reconciling expenses, you will constantly need to add GST to a price or work out how much GST a price includes. Both take one step once you know the trick — and the trick for removing GST is the one most people get wrong.
Open the free GST / VAT CalculatorAustralian GST in one line
GST in Australia is 10% on most goods and services. Some items — including most basic food, many health and education services — are GST-free.
How to add GST to a price
Multiply the GST-exclusive price by 1.1.
- $250 + GST = 250 × 1.1 = $275
- The GST amount is 250 × 0.1 = $25
How to remove GST from a price
To find the price before GST, divide the GST-inclusive price by 1.1. To find just the GST amount, divide the inclusive price by 11.
- $275 including GST ÷ 1.1 = $250 before GST
- GST included = 275 ÷ 11 = $25
The same method works for any rate
| Country | Standard rate | Add tax | Tax inside an inclusive price |
|---|---|---|---|
| Australia (GST) | 10% | × 1.1 | ÷ 11 |
| New Zealand (GST) | 15% | × 1.15 | × 3 ÷ 23 |
| United Kingdom (VAT) | 20% | × 1.2 | ÷ 6 |
| Singapore (GST) | 9% | × 1.09 | × 9 ÷ 109 |
The general rule: to add a rate of R%, multiply by (1 + R/100). The tax inside an inclusive price is price × R ÷ (100 + R). Rates change, so check your tax authority for the current figure. The GST & VAT Calculator has standard rates for 70 countries built in.
GST on invoices (Australia)
If you are registered for GST, your customers may need a tax invoice to claim GST credits. As a general guide, a tax invoice shows that it is a tax invoice, your business name and ABN, the date, a description of what was sold, the GST amount (or that the total includes GST) and — for larger sales — the buyer’s identity or ABN. Check the Australian Taxation Office’s current requirements for the details.
The Invoice Generator calculates tax automatically and exports a clean PDF.
Do I need to register for GST?
In Australia, businesses generally must register once their GST turnover reaches $75,000 a year ($150,000 for non-profits), and taxi and ride-share drivers must register regardless of turnover. Below the threshold registration is optional. Thresholds can change, so confirm with the ATO or a registered tax agent.
Worked example: a small invoice
| Item | Amount |
|---|---|
| Web design (10 hours at $90) | $900.00 |
| Hosting set-up | $150.00 |
| Subtotal (before GST) | $1,050.00 |
| GST (10%) | $105.00 |
| Total including GST | $1,155.00 |
Check it the other way round: $1,155 ÷ 11 = $105 of GST, and $1,155 ÷ 1.1 = $1,050 before GST.
Rounding
Calculate GST on the total of an invoice where you can, and round to the nearest cent. Rounding each line separately can make the total differ by a cent or two, which is normal, but be consistent.