NZ GST Component Calculator

Find the GST portion of a New Zealand price that already includes 15% GST.

Calculate the GST component

GST-inclusive amount (NZD):

Why 3 / 23?

A GST-inclusive price contains 15 parts GST for every 100 parts before GST, making 115 total parts. The GST share is therefore 15/115, which simplifies to 3/23.

Example

For NZ$1,150 including GST, the GST component is NZ$1,150 x 3 / 23 = NZ$150.

Worked example: checking a supplier invoice

A builder in Queenstown buys timber for $2,875 including GST and wants to know how much GST he can claim. Multiply by 3/23: $2,875 x 3/23 = $375.00 of GST, leaving $2,500.00 before GST.

He checks it backwards: $2,500 x 1.15 = $2,875. The numbers agree, so the invoice is consistent and he claims $375 in his next GST return.

When the GST component matters

You need the GST component whenever a price already includes GST and you have to split it out:

Working out how much GST you can claim back on business purchases.
Checking that a supplier’s invoice shows the right GST.
Quoting a GST-exclusive price from a GST-inclusive one.

This only works for standard 15% supplies. If the price involves zero-rated or exempt items, split those out first.

Quick examples at other prices

A $230 price including GST contains $30 of GST ($230 x 3/23) and $200 before GST. A $11,500 price contains $1,500 of GST and $10,000 before GST. A $46 price contains $6 of GST and $40 before GST.

A useful pattern to remember: for every $115 of GST-inclusive price, $15 is GST. So $1,150 contains ten lots of $15, which is $150.

NZ GST component calculator FAQs

What is the GST component?
It is the GST already built into a GST-inclusive price. For a $115 price, the component is $15 and the GST-exclusive amount is $100.

Why can’t I just take 15% off the inclusive price?
Because 15% of the inclusive price overstates the GST. For $115, that gives $17.25, which is wrong. The correct GST is $15, found with 3/23.

When should I not use this calculator?
Do not use it for zero-rated or exempt supplies, or to work out your whole GST return. It is a price-splitting tool for standard-rate amounts.

How do I double-check the answer?
Take the GST-exclusive figure and multiply by 1.15. If you land back on the original price, the split is right.

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