GST Calculator NZ

Calculating NZ GST: the three formulas

To calculate GST in New Zealand you need only three formulas, because the rate is a single 15% on almost everything that carries GST. Inland Revenue's own worked example uses $100 headphones: $100 × 0.15 = $15 GST, so the price including GST is $115. Working backwards, $115 × 3 ÷ 23 = $15.

• Add GST: price excluding GST × 1.15 = price including GST.
• GST in an inclusive price: price including GST × 3 ÷ 23 (the GST fraction).
• Remove GST: price including GST ÷ 1.15 = price excluding GST.

Why 3/23 and not 15%

The GST fraction is 3/23 because GST is 15/115 of a GST-inclusive price, and 15/115 reduces to 3/23 (about 13.04%). Taking 15% off an inclusive price is the most common mistake: 15% of $115 is $17.25, not $15, and $115 less 15% gives $97.75 rather than the true $100 ex-GST price. On a $25,000 invoice that error overstates the GST by $489.13.

GST included in common prices

Each row applies the 3/23 fraction to a GST-inclusive amount, as the calculator does in Remove GST mode.

Adding GST to a quote

If you are GST-registered and quote "plus GST", the customer pays your price × 1.15. A GST-registered business customer can usually claim that GST back in its own return; a consumer cannot, so for them the GST-inclusive figure is the real price.

Worked example: a six-monthly GST return

A GST return nets the GST you charged (output tax) against the GST you paid on business costs (input tax). Suppose a sole trader on the payments basis receives $82,800 including GST from customers over six months and pays $27,600 including GST on materials, fuel and phone. GST on sales is $82,800 × 3 ÷ 23 = $10,800; GST on expenses is $27,600 × 3 ÷ 23 = $3,600. The return shows $7,200 to pay. If expenses had been larger than sales – common in a start-up or capital-heavy period – the difference would be a GST refund.

Keep taxable supply information (what used to be called tax invoices) for every expense you claim; since 1 April 2023 the record-keeping rules are more flexible and can be met through e-invoicing, but the claim still needs a record behind it. A purchase used only partly in the business gets only a partial GST claim.

Zero-rated vs exempt supplies

Zero-rated and exempt supplies both carry no GST for the customer, but they are treated very differently in a GST return. Zero-rated supplies are taxable at 0%: you include them in your return and can still claim GST on the related costs. Exempt supplies sit outside GST altogether: you leave them out of the return and cannot claim GST on costs that relate to them.

GST filing frequency and due dates

Once your turnover reaches $60,000 in any 12 months you must register for GST (you can register voluntarily below that), and then you file a return for every period, even a nil one. Your filing frequency depends on turnover:

• Monthly – compulsory if sales exceed $24 million in any 12 months.
• Two-monthly – available to anyone under $24 million.
• Six-monthly – available if sales are under $500,000 in any 12 months.
• Payments basis (cash accounting) – allowed while annual sales stay at $2 million or less.

When GST returns and payments are due

A GST return and payment are due on the 28th of the month after the period ends – for example, a period ending 31 May is due 28 June. There are two exceptions: a period ending 31 March is due 7 May, and a period ending 30 November is due 15 January. Inland Revenue does not grant extensions for GST returns, and late filing and payment penalties apply. Your filing periods must line up with your income tax balance date, which for most businesses is 31 March.