GST on $20
Both answers, because "GST on $20" means two different things depending on whether that figure already includes GST.
How much GST is on $20?
- If $20 is before GST: GST is $3.00 and the total becomes $23.00.
- If $20 already includes GST: the GST portion is $2.61 and the price before GST is $17.39.
- Working: $20.00 × 1.15 = $23.00 · $20.00 ÷ 23 × 3 = $2.61
$20, worked both ways
| Treating $20 as… | GST | Ex GST | Inc GST |
|---|---|---|---|
| a price before GST | $3.00 | $20.00 | $23.00 |
| a total that includes GST | $2.61 | $17.39 | $20.00 |
| an Australian price at 10% | $2.00 | $20.00 | $22.00 |
The two NZ rows are the ones people mix up. Charging $3.00 of GST on an invoice whose total is meant to be $20 would leave you $0.39 short once Inland Revenue takes its cut — the GST inside $20 is only $2.61.
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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