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

Find the GST-exclusive amount and the 15% GST content from any New Zealand total. Enter a GST-inclusive figure to strip the GST out, or switch to add GST to an exclusive price. The calculator uses the IRD 3/23 method to extract the GST cleanly, which is the approach Inland Revenue uses and avoids rounding errors.

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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