New Zealand GST Calculator
Add or remove New Zealand GST instantly. Calculate GST at the standard 15% rate — enter a price and get GST-inclusive or GST-exclusive amounts.
Did this tool work for you?
How to use this calculator
- 1
Enter an amount in New Zealand dollars.
- 2
Choose “Add GST” if the amount excludes GST, or “Extract GST” if the amount already includes it.
- 3
Leave the rate at the default built into the tool, 15%, or type another rate to test a different percentage; a rate of 0 is respected.
- 4
Read the GST amount together with the price excluding GST and the price including GST. All three are shown to two decimal places.
Frequently asked questions
Which formulas does this tool use?
To add GST it multiplies the amount by the rate to get the GST, and the inclusive price is the amount plus that GST. To extract GST it divides by one plus the rate: GST = inclusive amount × rate ÷ (1 + rate), and the exclusive price is the inclusive amount minus that GST. At 15% the extraction fraction is 15 ÷ 115, which simplifies to 3 ÷ 23.
Why not just multiply a GST-inclusive price by 15%?
Because the GST is 15% of the exclusive price, not of the total. On $1,234.56 including GST the tool shows $161.03 of GST; taking 15% of $1,234.56 directly would give $185.18, which overstates it by $24.15. Use the extract option when the amount you hold already contains GST.
What rate does the tool use?
The default is 15%, the figure built into the tool, and you can overwrite it. The field accepts decimals, so 12.5% is shown as 12.5% in the label, not rounded. Clearing the rate box counts as 0%, which gives no GST and leaves the price unchanged. Negative rates are treated as zero. The tool never looks up a rate.
How does rounding work?
The tool works with unrounded values and rounds only for display, to two decimals. On rare occasions the displayed exclusive price and GST amount may therefore differ from the displayed total by one cent. Business records and invoices should follow your own rounding policy and Inland Revenue guidance.
Does the tool know whether GST applies?
No. It applies the rate to whatever number you enter. It does not know whether a supply is taxable, zero-rated or exempt, whether you are registered, or whether a particular cost can be claimed back. Those questions depend on your circumstances and are decided by Inland Revenue rules.
Can I use it for other countries?
The arithmetic works for any value-added or sales tax that is charged on top of a price, because you can type any percentage. Labels and currency symbol are fixed to New Zealand dollars, though, and other systems may have rounding or inclusion rules that this tool does not reproduce.
Does the rate stay current?
The default is a fixed value in the tool and is not updated automatically. Tax rates and rules can change, so check with Inland Revenue or a qualified adviser before relying on a figure for filing or invoicing.
GST arithmetic: adding to a price and extracting from one
Two directions, two formulas
Adding GST is a multiplication: GST = amount × rate, and the inclusive price is the amount plus that. Extracting GST is a division. When the price already includes GST, the exclusive price is the inclusive price ÷ (1 + rate), and the GST is whatever is left over, which is inclusive × rate ÷ (1 + rate). The default rate built into this tool is 15%, but the field is editable so you can test other percentages. Results are shown to two decimal places, rounded only for display.
Worked examples at 15%
Adding GST to $50 gives $7.50 of GST and a $57.50 total. Adding it to $1,234.56 gives $185.18 of GST and a total of $1,419.74. Extracting from the same $1,234.56 treated as GST-inclusive gives $161.03 of GST and an exclusive price of $1,073.53. The difference between the last two, $24.15, is the cost of using the wrong direction: multiplying an inclusive amount by 15% overstates the GST because the 15% belongs to the smaller exclusive price. At 12.5%, a $1,000 amount plus GST becomes $1,125.00, while extracting from $1,000 gives $111.11 of GST and $888.89 excluding.
Five runs side by side
The table puts adding and extracting next to each other. Rows two and three use the same amount of $1,234.56 and show how much the answer depends on the option selected, while the last two rows show that the same logic holds at a different percentage.
| Amount entered | Option and rate | GST amount | Price excluding GST | Price including GST |
|---|---|---|---|---|
| $50.00 | Add, 15% | $7.50 | $50.00 | $57.50 |
| $1,234.56 | Add, 15% | $185.18 | $1,234.56 | $1,419.74 |
| $1,234.56 | Extract, 15% | $161.03 | $1,073.53 | $1,234.56 |
| $1,000.00 | Add, 12.5% | $125.00 | $1,000.00 | $1,125.00 |
| $1,000.00 | Extract, 12.5% | $111.11 | $888.89 | $1,000.00 |
What the tool cannot determine
It does not know whether a supply is taxable, whether you are registered, which return period applies or how much can be claimed as input tax. It treats the number you type as the only fact. It handles one line at a time, so a multi-line invoice with mixed treatment needs separate runs. Check the tax status of your supplies separately.
About the default rate
The default rate of 15% is the figure built into this tool and is not updated automatically. Tax rules can change, so Inland Revenue, or a qualified adviser, governs how GST applies to your own sales and purchases. The calculator is only a way to run the arithmetic quickly and consistently.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →