GST on $100: Added, Included, and the Tax Invoice Line

Just above the $82.50 tax invoice line

Section 29-80 of the GST Act removes the need for a tax invoice when the value of the taxable supply does not exceed a set amount, which regulation 29-80.01 fixes at $75. Value means the price before GST, so the test on a GST-inclusive receipt is $82.50. A $100 purchase has a value of $90.91: over the line. For a business buying office supplies, fuel or a software subscription at around $100, the docket from the counter is not enough if it lacks the supplier's ABN and the GST; ask for a tax invoice, or download it from the supplier's account.

Why the cents land where they do

$100 ÷ 11 is 9.0909… dollars. Section 9-90 rounds GST to the nearest cent, half a cent up, so the GST is $9.09 and the value $90.91. Going the other way, 10% of $100 is exactly $10.00, no rounding needed. That is why a price list built on round ex GST figures ($100, $200, $500) gives clean GST amounts, while one built on round GST-inclusive prices gives cents.

Two prices people confuse

A tradesperson quoting "$100 an hour" to a household and a supplier quoting "$100 + GST" to a business are not asking the same price. The first should be $100 all in; the second is $110.00. If a quote says neither, ask before work starts. For an invoice with several amounts, use the GST calculator; for a docket that mixes GST-free items, the reverse GST calculator.