GST on $100
Both answers, because "GST on $100" means two different things depending on whether that figure already includes GST.
How much GST is on $100?
- If $100 is before GST: GST is $15.00 and the total becomes $115.00.
- If $100 already includes GST: the GST portion is $13.04 and the price before GST is $86.96.
- Working: $100.00 × 1.15 = $115.00 · $100.00 ÷ 23 × 3 = $13.04
$100, worked both ways
| Treating $100 as… | GST | Ex GST | Inc GST |
|---|---|---|---|
| a price before GST | $15.00 | $100.00 | $115.00 |
| a total that includes GST | $13.04 | $86.96 | $100.00 |
| an Australian price at 10% | $10.00 | $100.00 | $110.00 |
The two NZ rows are the ones people mix up. Charging $15.00 of GST on an invoice whose total is meant to be $100 would leave you $1.96 short once Inland Revenue takes its cut — the GST inside $100 is only $13.04.
The two calculations
Adding GST to a GST-exclusive price.
Finding the GST already inside a total.
Stripping GST out to get the ex-GST price.
Taking 15% of a GST-inclusive figure is the common error — it overstates the GST every time. Full guide, with the registration rules and the $60,000 threshold →
Do the next bit too
The number is the easy part. These take it the rest of the way.
Make the invoice
Turn this figure into a compliant GST tax invoice with your logo and download the PDF. The amount carries across automatically.
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Hnry takes your income, works out the GST, ACC and income tax, pays them and files the returns. Built for NZ sole traders.
See Hnry →GST on other amounts
The rest of the toolkit
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