The rule for consumers
Under the Australian Consumer Law you must state a single total price whenever you quote or advertise a price to a consumer: the minimum amount they'll pay, including GST and any unavoidable charges. You may show the components ("$1,200 + $120 GST") as long as the total ($1,320) is at least as prominent.
"Two hours, $90 plus GST" in a text message to a homeowner is a price representation to a consumer. The ACCC's guidance is blunt: prices quoted to the general public should include GST, and saying that 10% will be added at payment can mislead. Breaches carry penalties.
The rule for businesses
If you only quote to other businesses, you may leave GST out of the headline figure, because they claim it back and compare prices without it. Say so on the document: "All prices exclude GST", or "+ GST" on every line. The exception disappears the moment the same price is put in front of consumers: on your website, on social media, on a flyer.
If you're not registered for GST
Then there is no GST to add. Quote the full price and never write "plus GST": you can't charge it, and a customer who pays it can't claim it.
What "$1,200" means when you didn't say
If you're registered and the quote just said $1,200, treat it as inclusive. The customer certainly will. That $1,200 contains $109.09 of GST (divide by 11), and $1,090.91 is yours. Invoicing $1,320 after the fact is where the argument starts, and with a consumer it's an argument you lose.
Worked example
The same $1,200 quote, three ways.
| Quote said | Customer | Invoice total | GST on the invoice | You keep |
|---|---|---|---|---|
| "$1,200 including GST" | anyone | $1,200.00 | $109.09 | $1,090.91 |
| "$1,200 + GST" | a business | $1,320.00 | $120.00 | $1,200.00 |
| "$1,200" | anyone | $1,200.00 | $109.09 | $1,090.91 |
Quoted "$1,200 + GST" to a household? The ACCC's rule is that $1,320 should have been the prominent figure. Put it there on the next quote.
Wording that ends the argument
Paste one of these on every quote, and say it out loud when you quote over the phone:
- Registered, quoting a household: "Total $1,320.00 including GST."
- Registered, quoting a business: "All prices exclude GST. GST of 10% ($120.00) applies; total $1,320.00."
- Not registered: "No GST has been charged. This business is not registered for GST."