NZ Reverse GST Calculator
A reverse GST calculation starts from a GST-inclusive total and works out how much of it is GST and how much is the underlying GST-exclusive price. In New Zealand, GST is 15%, so an inclusive price is 115% of the exclusive price. To find the GST, divide the inclusive total by 23 and multiply by 3; to find the exclusive amount, divide the total by 1.15. This is the calculation you need when a receipt or quoted price already includes GST and you want to record the GST separately, for example on a business expense. Enter a GST-inclusive amount below to see the GST content and the exclusive price. The 15% rate traces to the Inland Revenue GST pages, checked on the date shown.
A GST-inclusive total of $115.00 contains $15.00 of GST, leaving $100.00 exclusive.
Applies to: New Zealand GST at the standard 15% rate. Source: Inland Revenue GST, checked 20 June 2026.
What this tool does
It takes a GST-inclusive total and splits it into the 15% GST content and the GST-exclusive amount.
The formula
GST content = inclusive x 3 / 23
GST-exclusive = inclusive / 1.15
(the two are consistent: inclusive - exclusive = GST content)
GST rate (Inland Revenue)
| Item | Value | Source |
|---|---|---|
| Standard GST rate | 15% | IRD GST, checked 20 June 2026 |
| Inclusive to GST ratio | 3 / 23 | IRD charging GST, checked 20 June 2026 |
Worked example
An invoice total of 230 dollars including GST:
- GST content = 230 x 3 / 23 = 30.00
- GST-exclusive = 230 / 1.15 = 200.00
- Check: 200 + 30 = 230.00, matching the inclusive total
Who this is for
Anyone recording the GST inside a GST-inclusive receipt or quoted price, such as sole traders coding expenses or buyers checking an invoice.
What this assumes
It assumes the input is a GST-inclusive amount at the standard 15% rate. It does not handle zero-rated or exempt supplies.
Reverse GST: frequently asked questions
How do I work out the GST in a GST-inclusive price?
Divide the inclusive total by 23 and multiply by 3, which gives the GST. Equivalently, divide the total by 1.15 to get the GST-exclusive amount, then subtract it from the total.
Why divide by 23 and multiply by 3?
At 15% GST, an inclusive price is 115% of the exclusive price, a ratio of 23 to 20. The GST is 3 parts out of those 23, so GST equals the inclusive total times 3 divided by 23.
What is the GST in 115 dollars?
115 divided by 23 times 3 is 15 dollars. The GST-exclusive amount is 100 dollars.
Is this the same rate as the forward GST calculator?
Yes. Both use the standard 15% New Zealand GST rate. This tool starts from a GST-inclusive total and works backwards.
Is the rate official?
Yes. The 15% rate is published by Inland Revenue, checked live on 20 June 2026.
Official sources and verification
- GST rate: Inland Revenue, GST, checked 20 June 2026.
- Charging GST: Inland Revenue, charging GST, checked 20 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 20 June 2026. See our methodology. General information, not tax advice.