GST on $120
Both answers, because "GST on $120" means two different things depending on whether that figure already includes GST.
How much GST is on $120?
- If $120 is before GST: GST is $18.00 and the total becomes $138.00.
- If $120 already includes GST: the GST portion is $15.65 and the price before GST is $104.35.
- Working: $120.00 × 1.15 = $138.00 · $120.00 ÷ 23 × 3 = $15.65
$120, worked both ways
| Treating $120 as… | GST | Ex GST | Inc GST |
|---|---|---|---|
| a price before GST | $18.00 | $120.00 | $138.00 |
| a total that includes GST | $15.65 | $104.35 | $120.00 |
| an Australian price at 10% | $12.00 | $120.00 | $132.00 |
The two NZ rows are the ones people mix up. Charging $18.00 of GST on an invoice whose total is meant to be $120 would leave you $2.35 short once Inland Revenue takes its cut — the GST inside $120 is only $15.65.
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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The rest of the toolkit
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