How to Calculate GST in Australia: Add 10%, Divide by 11

Short answer: To calculate GST in Australia, take 10% of the price before GST, or multiply that price by 1.1 to get the GST-inclusive total. To find the GST inside a GST-inclusive total, divide it by 11, and to get the price before GST, divide the total by 1.1. So $500 plus GST is $550, of which $50 is GST. The rate is the same 10% in every state, and you only charge it once you’re registered for GST.

GST is a federal tax of 10% on most goods, services and other items sold or consumed in Australia, and the Australian Taxation Office (ATO) administers it. The rate is the same for the 2025–26 and 2026–27 income years, so the maths below works for anything you’re pricing, quoting or checking now. It’s written for sole traders and small businesses, whether you’re pricing a job, invoicing it or checking a receipt. For what has to appear on the invoice itself, see how to invoice as a sole trader. For where these numbers end up each quarter, see what a BAS is.

How do you add GST to a price?

Multiply the price excluding GST by 1.1. That adds 10% in one step and gives you the GST-inclusive total. If you want the GST on its own, multiply by 0.1 instead.

• GST = price excluding GST × 0.1
• Price including GST = price excluding GST × 1.1

A tiler quoting $1,840 of labour and $1,260 of materials has $3,100 excluding GST. The GST is $310 and the client pays $3,410. Work out the GST on the subtotal, not on each line in your head, and show it once. Our quote template is laid out that way.

How do you calculate the GST from a total?

Divide the GST-inclusive total by 11. Because GST is 10% of the pre-GST price, it’s one-eleventh of the total once it’s been added. The ATO uses this method itself: when a tax invoice only says the price includes GST, you work out the GST by dividing the price by 11.

• GST in a total = GST-inclusive total ÷ 11

A $190 receipt that says “includes GST” contains $17.27 of GST, since $190 ÷ 11 = $17.2727, rounded to $17.27. This is the calculation you’ll do most often: on supplier receipts, on payments you’ve received and on your own quarterly figures.

How do you work out the price excluding GST?

Divide the GST-inclusive total by 1.1. You get the same answer by subtracting the GST, so total − (total ÷ 11).

• Price excluding GST = GST-inclusive total ÷ 1.1

A $350 total is $318.18 excluding GST, and the GST is $31.82. The two figures always add back to the total, which is a quick way to check your working: $318.18 + $31.82 = $350.00.

What do GST calculations look like in practice?

The two tables below cover both directions. In the first you start from a price before GST; in the second you start from a total that already includes it.

Adding GST to a price

Price excluding GST	GST (× 0.1)	Total including GST (× 1.1)
$100.00	$10.00	$110.00
$450.00	$45.00	$495.00
$1,250.00	$125.00	$1,375.00
$3,100.00	$310.00	$3,410.00
$49.95	$5.00 (4.995, rounded)	$54.95

Taking GST out of a total

Total including GST	GST (÷ 11)	Price excluding GST (÷ 1.1)
$110.00	$10.00	$100.00
$82.50	$7.50	$75.00
$190.00	$17.27	$172.73
$350.00	$31.82	$318.18
$1,000.00	$90.91	$909.09
$27,500.00	$2,500.00	$25,000.00

If you’d rather use a spreadsheet than a calculator, these formulas do the same work, with the amount in cell A2:

To get	Spreadsheet formula
GST on a price excluding GST	=ROUND(A2*0.1,2)
Total including GST	=ROUND(A2*1.1,2)
GST inside a GST-inclusive total	=ROUND(A2/11,2)
Price excluding GST from a total	=ROUND(A2/1.1,2)

What are the most common GST calculation mistakes?

The most common mistake is taking 10% of a total that already includes GST. GST is 10% of the price before GST, so 10% of the total overstates it.

Mistake	On a $1,100 total	Correct
Taking 10% of the total as the GST	$110 GST	$1,100 ÷ 11 = $100 GST
Subtracting 10% to get the ex-GST price	$990	$1,100 ÷ 1.1 = $1,000
Adding GST to a price that already includes it	$1,210	$1,100 stays $1,100

Three other errors come up often:

• Charging GST before you’re registered. If you’re not registered, you don’t add GST and you don’t issue tax invoices. Registration becomes compulsory at $75,000 GST turnover, and you then have 21 days to register.
• Quoting consumers a price that leaves GST out. When you advertise a price to consumers, business.gov.au says the total price must include all taxes, GST included. “$500 + GST” on a sign aimed at households is a problem.
• Dividing a mixed total by 11. This only works when everything in the total is taxable. See the GST-free section below.

How does rounding work when you calculate GST?

Round to the nearest cent, and round half a cent up. That’s the ATO rule when an invoice has a single taxable sale: $49.95 × 0.1 = $4.995, which rounds to $5.00.

When an invoice has several taxable sales, the ATO allows two methods:

• Total invoice rule: add up the GST-exclusive values, work out the GST on that total and round once. You can use this when every taxable item carries GST at exactly one-eleventh of its price.
• Taxable supply rule: work out the GST on each item, add those amounts together and round the total to the nearest cent.

You and your customer don’t have to use the same rule. A difference of a cent between your figure and theirs isn’t an error.

When should you not add GST at all?

Don’t add GST if you aren’t registered for GST, or if what you’re selling is GST-free or input-taxed.

• GST-free sales include most basic food, some education courses and some medical, health and care products and services. You charge no GST, but you can still claim GST credits on what you bought to make the sale.
• Input-taxed sales, mainly financial supplies and residential rent, carry no GST, and you can’t claim credits on the inputs.

Mixed invoices are where the divide-by-11 shortcut fails. Say an invoice has $600 of taxable items (excluding GST) and $80 of GST-free items. The GST is $60, on the taxable part only, and the total is $740. Dividing $740 by 11 gives $67.27, which is wrong. That’s why the ATO lets a tax invoice simply say “total price includes GST” only when the GST is exactly one-eleventh of the total. A mixed invoice has to show which items are taxable and how much GST is payable.

How does the GST you calculate end up on your BAS?

On each BAS you report the GST you collected on sales at label 1A and the GST you paid on business purchases at 1B. The difference is the GST you pay, or the refund you get.

Say a sole trader receives $27,500 including GST in a quarter. The GST on sales is $27,500 ÷ 11 = $2,500 at 1A. Their business purchases came to $7,040 including GST, so the GST credits are $7,040 ÷ 11 = $640 at 1B. Their net GST for the quarter is $1,860, payable to the ATO.

To claim a credit on a purchase that cost more than $82.50 including GST, you need a valid tax invoice from the supplier. That’s why $82.50 sits in the table above: it’s $75 plus GST. Expenses and receipts for sole traders covers keeping those documents, and how to do a BAS walks through the labels.

Where do the GST figures live, and where does Keel fit?

Every GST figure on a BAS comes from an invoice you issued or a receipt you kept, and if one is missing, you can’t back up the number.

Keel: Invoice Maker & Receipts, by Ilura Technology OÜ, is an iPhone app for keeping those documents. You write estimates, and an accepted estimate becomes the invoice in one tap. Each invoice is a PDF, and receipts and expenses are filed under the job they belong to. Mileage is logged as well, and a “who owes you” list drafts reminders that you review and send yourself. Records stay on your iPhone: there’s no account, no bank connection and no cloud sync, and the App Store privacy label reads “Data Not Collected”.

Keel doesn’t calculate the tax you owe, lodge your BAS or connect to the ATO. It’s a record keeper. It’s free with no invoice limit, and free invoices carry a small “Made with Keel” footer. Keel Lifetime is a one-time purchase ($249.99 USD; the App Store shows your local price) that adds custom branding, a signature, premium templates and accountant-ready exports. Keel on the App Store. There’s more on GST, ABNs and BAS in the Australia guides.

Frequently asked questions

How do I calculate GST from a total? Divide the GST-inclusive total by 11. Because GST is 10% of the price before tax, it makes up one-eleventh of the final total. A $1,100 total contains $100 of GST, and a $190 total contains $17.27. Round to the nearest cent, rounding half a cent up. This works only when everything in the total is taxable at the full rate.

How do I work out a price excluding GST? Divide the GST-inclusive total by 1.1, or subtract one-eleventh of the total. A $350 total is $318.18 excluding GST, with $31.82 of GST. The two figures should always add back to the original total, so adding them is a quick check. Subtracting 10% from the total gives the wrong answer, because it takes off too much.

Is GST 10% of the total price? No. GST is 10% of the price before GST, which works out to one-eleventh of the GST-inclusive total, or about 9.09% of it. On a $1,100 total the GST is $100, not $110. Taking 10% of a total that already includes GST is the most common GST calculation mistake, and it overstates both what you collected and what you can claim.

Is GST calculated differently in NSW or Queensland? No. GST is a federal tax, so the rate is 10% in New South Wales, Queensland and every other state and territory, and the same maths applies everywhere. A “GST calculator NSW” and a “GST calculator QLD” do exactly the same thing. State taxes such as stamp duty and payroll tax are separate and don’t change how you calculate GST.

Do I add GST to my invoices if I am not registered for GST? No. If you aren’t registered for GST, you don’t add GST, you don’t show a GST amount and you don’t call the document a tax invoice. Registration becomes compulsory once your GST turnover reaches $75,000, current or projected, and you then have 21 days to register. Ride-sourcing drivers must register before their first trip, whatever they earn.

Can I claim back the GST on things I buy for my business? Yes, once you’re registered for GST, you can claim the GST included in the price of business purchases as GST credits on your BAS. For anything that cost more than $82.50 including GST, you need a valid tax invoice from the supplier. Work out the credit by dividing the GST-inclusive price by 11, and keep the document as your record.

---

This article is general information, not tax advice. Consult a qualified Australian tax professional.