GST calculator. Add the 10%, or take it back out of a total. The GST inside a price is one eleventh of it, not one tenth, and this does the sum properly.
| Without GST | GST | With GST |
|---|---|---|
| $10.00 | $1.00 | $11.00 |
| $25.00 | $2.50 | $27.50 |
| $50.00 | $5.00 | $55.00 |
| $100.00 | $10.00 | $110.00 |
| $250.00 | $25.00 | $275.00 |
| $500.00 | $50.00 | $550.00 |
| $1,000.00 | $100.00 | $1,100.00 |
| $2,500.00 | $250.00 | $2,750.00 |
| $5,000.00 | $500.00 | $5,500.00 |
| $10,000.00 | $1,000.00 | $11,000.00 |
Australian figures, checked 19 September 2026. Nothing you type leaves your browser.
The one-eleventh rule.
GST in Australia is 10%. Adding it is easy: multiply the price by 1.1. Taking it out of a price that already includes it is where people slip. The GST is a tenth of the price before GST, which makes it one eleventh of the price after. So a $1,100 total holds $100 of GST, and dividing by 10 to get $110 overstates it.
Businesses registered for GST charge it on most sales, pay it on most purchases, and settle the difference with the ATO on their BAS. Anyone can use this calculator: for checking a quote, reading a receipt, or writing an invoice by hand at ten o'clock at night.
What the numbers mean.
Price without GST
The ex-GST amount. What you actually earn on a sale before the tax that passes through to the ATO.
GST
The 10%. Collected on sales, paid on purchases, and the difference goes on your activity statement.
Price with GST
The GST-inclusive amount. What a customer pays, and what has to appear on a consumer price tag.
Registration
Required at $75,000 turnover a year, $150,000 for non-profits. Optional below that, and sometimes worth it.
Tax invoices
Over $82.50 including GST an invoice needs your ABN, the words "tax invoice" and the GST shown. Over $1,000, the buyer's details too.
GST-free
Basic food, most health, most education, exports. No GST charged, but you still claim the GST on what it cost you to supply.
Or never do this sum again.
If you're here because an invoice needs writing, the better fix is invoices that write themselves. The job's marked done, the invoice goes out with the GST right, and it gets chased if it's late. That's automated invoicing, and it's most of what we build for tradies and small businesses.
Questions people ask.
How do I work out the GST in a price that already includes it?
Divide the total by 11. A $1,100 invoice has $100 of GST in it, and the price before GST was $1,000. Dividing by 10 is the common mistake; that gives $110, which is wrong.
How do I add GST to a price?
Multiply by 1.1, or add 10%. $1,000 before GST is $1,100 with it. The GST is $100.
Do I have to register for GST?
You must register once your business turnover reaches $75,000 a year ($150,000 for non-profits), or straight away if you drive for a rideshare or taxi service. Under that you can choose to register, which lets you claim the GST on what you buy but means charging it on what you sell.
What has to be on a tax invoice?
For sales of $82.50 or more (including GST): the words "tax invoice", your business name and ABN, the date, a description of what was sold, the GST amount or a statement that the total includes GST, and for sales over $1,000 the buyer's name or ABN too.
What is GST-free?
Most basic food, most health and medical services, most education courses, childcare, exports and some other things. Financial supplies and residential rent are input-taxed, which is different: no GST is charged but you can't claim the GST on related costs either. When in doubt, check the ATO's list or ask your accountant.
When do I pay the GST I've collected?
On your business activity statement, usually every quarter. You pay the GST you collected on sales minus the GST you paid on business purchases. The BAS calculator on this site works that out.
Photo to come: Cal.
Calum Buchanan.
Melbourne. Ran the systems behind a services business, the phones, the invoices, the marketing, the reporting, and spent the last few years handing them to AI that works. This is that, for yours.