How do I find the GST-exclusive amount?

Divide the GST-inclusive total by 1.15. For example, a $115 total divided by 1.15 is $100 GST-exclusive, with $15 of GST. Do not subtract 15%, which gives the wrong answer.

What is the IRD 3/23 method?

To extract the GST content from a GST-inclusive total, multiply the total by 3 and divide by 23. For $115, that is 115 times 3 divided by 23, which equals $15. This is the method Inland Revenue uses and avoids rounding drift.

Why is 15% of the total not the GST?

Because the GST is 15% of the exclusive price, not the inclusive total. Taking 15% of a $115 total gives $17.25, which is too high. The correct GST is $15, found by dividing by 1.15 or using the 3/23 fraction.

GST Exclusive Calculator

This calculator finds the GST-exclusive amount and the 15% GST content from any New Zealand price, or works the other way and adds GST onto an exclusive figure, so you always know exactly how a total splits between GST and the underlying charge. It matters whenever you are pricing invoices, checking a supplier bill, filling in a GST return, or simply want to know how much of a receipt is tax. You choose whether your figure is GST-inclusive (to remove GST) or GST-exclusive (to add GST), then enter the dollar amount. If you are removing GST, the calculator returns the GST-exclusive amount as the headline result, alongside the GST content at 15 percent and the original GST-inclusive total for reference. If you are adding GST, it flips around and shows the GST-inclusive total as the headline figure, with the GST content and your original exclusive amount underneath. The maths follows the method Inland Revenue uses: dividing an inclusive total by 1.15 gives the exclusive amount, and multiplying by 3 then dividing by 23 gives the GST content directly, both of which avoid the rounding drift that comes from simply taking 15 percent off the total. For example, a $115 GST-inclusive total is $100 exclusive of GST, with $15 of GST content. Use it to check invoices, prepare a GST return, or quote a price either way with confidence.

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Your amount is

Amount

$100.00

GST-exclusive amount

GST content (15%)$15.00

GST-inclusive total$115.00

How to remove GST

To find the GST-exclusive amount, divide the GST-inclusive total by 1.15. To find the GST content directly, multiply the total by 3 and divide by 23 (the IRD method). Both give the same answer. To add GST to an exclusive price, multiply by 1.15.

Worked example

A $115 invoice total divided by 1.15 is $100 GST-exclusive, leaving $15 of GST. Using the 3/23 fraction, 115 times 3 divided by 23 is also $15.

Frequently asked questions

Why not just take 15% off?

Because the GST is 15% of the exclusive amount, not the total. Taking 15% of the total over-states the GST. Always divide by 1.15 or use 3/23.

Related calculators

GST Calculator: add or remove GST with full examples.
Reverse GST Calculator: extract GST from a total.
GST Registration Threshold: the $60,000 rule.
PAYE Calculator: take-home pay after tax.

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