GST on $600
Both answers, because "GST on $600" means two different things depending on whether that figure already includes GST.
How much GST is on $600?
- If $600 is before GST: GST is $90.00 and the total becomes $690.00.
- If $600 already includes GST: the GST portion is $78.26 and the price before GST is $521.74.
- Working: $600.00 × 1.15 = $690.00 · $600.00 ÷ 23 × 3 = $78.26
How to work out GST in your head
There are only two calculations, and they are not symmetrical — which is where nearly every GST mistake comes from.
Adding GST. Your price is GST-exclusive and you want the total. $200 × 1.15 = $230. The GST itself is $30.
Finding the GST inside a price. The total already includes GST. $230 ÷ 23 × 3 = $30. This is the one worth memorising.
Stripping GST out. Gives the GST-exclusive price. $230 ÷ 1.15 = $200. Same job as above, different output.
The mistake that costs real money
If a client agreed to pay you $1,150 including GST, the GST is not 15% of $1,150. Fifteen percent of $1,150 is $172.50, but the correct GST is $150 — because the GST-exclusive price was $1,000. Taking 15% of an inclusive figure overstates the GST by 15% every single time.
It matters in both directions. Overstate the GST and you hand Inland Revenue money that was your income. Understate it and you have a shortfall to make up at return time out of money you have already spent.
GST at a glance
| Amount | + GST | Total | GST inside | Ex GST |
|---|---|---|---|---|
| $100.00 | $15.00 | $115.00 | $13.04 | $86.96 |
| $250.00 | $37.50 | $287.50 | $32.61 | $217.39 |
| $500.00 | $75.00 | $575.00 | $65.22 | $434.78 |
| $1,000.00 | $150.00 | $1,150.00 | $130.43 | $869.57 |
| $2,500.00 | $375.00 | $2,875.00 | $326.09 | $2,173.91 |
| $5,000.00 | $750.00 | $5,750.00 | $652.17 | $4,347.83 |
Left three columns treat the amount as GST-exclusive. Right two treat the same figure as a GST-inclusive total.
Do you need to register for GST?
In New Zealand, registration becomes compulsory once your turnover passes $60,000 in any twelve-month period. That test looks backwards over the last twelve months and forwards over the next twelve, so a single large contract that will clearly push you over the line triggers it even before the money arrives.
Below the threshold it is a genuine choice, and the right answer depends entirely on who your customers are:
- Selling to GST-registered businesses? Register. They claim the GST back, so your price does not effectively change for them, and you get to claim GST on your own costs.
- Selling to consumers? Usually do not. Registering means either raising your price 15% or absorbing it — and consumers cannot claim anything back.
- Large startup costs? Registering early lets you claim the GST on equipment and setup, which can be worth thousands in year one.
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.
invoice.amit.marketing →Send a quote first
Price the job, send a professional quote, and convert it to an invoice in one click when the client says yes.
quote.amit.marketing →Never file a GST return again
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 questions, answered
How do I calculate 15% GST in New Zealand?
What is the divide by 23 multiply by 3 rule?
Is GST 15% on everything in New Zealand?
When do I have to register for GST?
Why does adding then removing GST not return the same number?
What GST rate does Australia use?
Does the calculator store what I type?
GST on common amounts
The rest of the toolkit
Ten free tools that talk to each other — send hours or an accepted quote straight into an invoice without retyping a thing. No signup on any of them.