How do I calculate GST in Australia?

To add GST, multiply the price by 1.1. To take GST out of a GST-inclusive price, divide by 11 to get the GST, or divide by 1.1 to get the price before GST. GST in Australia is 10% of the GST-exclusive price, which is the same as one-eleventh of the GST-inclusive price.

How do I add GST to a price?

Multiply the GST-exclusive price by 1.1. The GST is 10% of the price before GST, and the total is that price plus the GST.

Example: a job priced at $850 before GST.

• GST: $850 × 0.10 = $85
• Total: $850 + $85 = $935 (or $850 × 1.1)

Only add GST if you are registered for it. If you are not sure whether you need to be, read when to register for GST.

How do I work out the GST in a price that already includes it?

Divide the GST-inclusive price by 11. Do not take 10% of the total, because that overstates the GST.

Example: a customer pays $1,100 including GST.

• GST: $1,100 ÷ 11 = $100
• Price before GST: $1,100 − $100 = $1,000

The ATO's ruling on the subject (GSTR 2001/8) explains that GST on a taxable supply is one-eleventh of its price, which is why the divide-by-11 method works.

How do I remove GST from a price?

Divide the GST-inclusive price by 1.1, or subtract the GST you worked out by dividing by 11. Both give the same answer.

Example: $330 including GST.

• $330 ÷ 1.1 = $300 before GST
• GST is $30

Why is taking 10% off a GST-inclusive price wrong?

Because 10% of the total is more than the real GST. On $1,100, 10% is $110, but the GST is $100. If you quote on that basis, you under-charge yourself by $10 on every $1,100 and your BAS will not add up.

If the price is...	GST is...	Quick method
Before GST (ex GST)	10% of the price	× 0.1, or × 1.1 for the total
Including GST (inc GST)	one-eleventh of the price	÷ 11, or ÷ 1.1 for the ex-GST price

How should I round GST on an invoice with several lines?

Add up the GST-exclusive amounts first, work out the GST on the total, then round to the nearest cent. The ATO's guidance for invoices with several taxable items is to do it this way, rounding half a cent upwards, rather than rounding the GST on each line.

Example: three lines of $33.33, $45.45 and $12.12 before GST. The total is $90.90, so the GST is $9.09 and the invoice total is $99.99.

What if part of the sale is GST-free?

Then the GST is less than one-eleventh of the total, so you cannot divide the whole invoice by 11. Calculate GST only on the taxable lines and show the GST-free lines separately. Some supplies, such as basic food, are GST-free, and others are input-taxed. Most trade work is taxable. If you are unsure about a particular item, ask your accountant or check with the ATO.

What does GST look like on a tax invoice?

For a sale under $1,000, the ATO lets you write "Total price includes GST" instead of showing a separate GST amount, as long as the GST is exactly one-eleventh of the total. For $1,000 or more, the invoice must show the GST amount or the GST-exclusive price. The full list of what an invoice must show is in tax invoice requirements in Australia.

Can software do the GST maths for me?

Yes, and it removes the most common slip, which is dividing by the wrong number late at night. Invogo adds GST and your verified ABN to every invoice automatically, so you enter the price and it shows the GST and total. The free plan covers 5 invoices or quotes a month, with no card needed. You can create a free account and try it on your next job. Tradies in a specific trade can also see the plumber or electrician pages for examples.

This is general information, not advice. Check with your accountant or the ATO for your situation.