Who this is for
Contractors, consultants, cleaners, online sellers, creators, agents and anyone whose sales are approaching or have passed $30,000. Our GST registration guide has worked examples; this one lists the mistakes.
The seven mistakes
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Measuring profit. The test is on taxable supplies: what you charged customers for taxable goods and services, before any expenses.
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Missing the single-quarter test. One big quarter over $30,000 means immediate registration, effective no later than the sale that took you over. It does not matter what the other quarters look like.
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Miscounting the four quarters. The second test adds the last four calendar quarters together, on a rolling basis. It is not a calendar year total. Each quarter end, add the last four.
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Not knowing when charging starts. Under the four-quarter test, you stop being a small supplier at the end of the month after the quarter that took you over. Your first sale after that must include GST. Under the single-quarter test, the sale that took you over already includes it.
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Forgetting zero-rated sales count. Basic groceries, exports and services to non-residents can be zero-rated, charged at 0%. They are still taxable supplies and count toward the $30,000.
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Treating registration as optional after the line. It is not. You have 29 days from the effective date to register, and GST is owed from that date whether or not you collected it.
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Ignoring voluntary registration before the line. Registering early lets you claim back GST on equipment, rent and other costs. For a business selling to other businesses, or buying a lot of equipment at the start, it can be worth it.
One thing many people do not realize
There are two different $30,000 tests, with different timing. Pass $30,000 inside one calendar quarter and you stop being a small supplier on the very sale that took you over. GST applies to that sale. Pass $30,000 only across four quarters together and you stop being a small supplier at the end of the month after that quarter. People who know the number rarely know the timing, and the timing decides what is owed.
What to prepare
- Sales by calendar quarter for the last five quarters
- What kind of goods or services, and whether any are zero-rated or exempt
- Whether you already have a business number
- Expected sales for the next two quarters
When professional help may make sense
If you crossed the line in a past quarter and did not register, the GST for the period since is owed. The cost is smaller the sooner it is handled, and the Voluntary Disclosures Program can apply.
How Rex Tax may be able to help
We register you, set the effective date correctly, set up the filing schedule, and prepare the returns. Our guide on GST for food products covers the zero-rated question for food businesses.
Official sources
This guide is general information, not advice about your situation. It reflects the rules for the 2026 tax year. It has not yet been reviewed by a practitioner. The information was checked against the official sources listed above on the date shown. Rules change. Check the official sources above or ask us. How we prepare these guides.