GST, the Goods and Services Tax, is a 10 per cent tax on most goods and services sold in Australia. A business registered for GST includes it in its prices, pays the GST it collects to the ATO, and claims back the GST it paid on its own business purchases, such as materials, fuel and tools. A business must register once its GST turnover reaches $75,000 a year, and can choose to register below that. A business that is not registered cannot charge GST and must not show it on a quote or invoice.
In practice
For a trade quoting homeowners, the plain approach is to quote prices that already include GST and say so. A homeowner cannot claim the GST back, so the number that matters to them is the total they will pay. Business customers often think in prices before GST, because they claim the GST back, so a quote to a builder or a property group may show both.
To find the GST inside a GST-inclusive price, divide by 11. A quote total of $1,320 including GST contains $120 of GST, and the price before GST is $1,200. To add GST to a price that excludes it, multiply by 1.1: $2,400 before GST becomes $2,640.
Most GST arguments on trade jobs come from silence. A quote that says $4,800 with no mention of tax lets the customer believe it includes GST and the trade believe it does not, and the gap is $480. One sentence settles it either way: "Price includes GST", or "We are not registered for GST". If you are close to the registration threshold, keep an eye on it monthly, because crossing it changes what you must charge from that point on. For anything about when to register or how to account for GST, check with the ATO.
In Quote Desk
Quote Desk does no tax calculation and adds no GST line. A quote's total is the sum of its lines, so registered businesses enter GST-inclusive prices on the price list and state that in the note. See GST, quantities and what the builder does not do.