How to calculate GST in New Zealand: add, remove and check 15% GST
By GrowThenDraw Editorial Team · Updated August 11, 2026 · 8 min read · Editorial policy
New Zealand's standard GST rate is 15%. The arithmetic is simple once you know whether the starting price excludes GST, includes GST or represents the GST component alone.
The harder question is whether standard-rate GST applies to the transaction. This guide explains the arithmetic and the calculator's limits; it does not determine registration or classify a supply.
Add GST to a price that excludes GST
Multiply the exclusive price by 0.15 to find the GST. Add that result to the exclusive price, or multiply the exclusive price by 1.15 to reach the inclusive total.
Example: a $200 exclusive price has $30 GST. The inclusive total is $230. For multiple units, multiply the unit amount by quantity first, apply any genuine pre-GST discount, then calculate GST on the discounted exclusive subtotal.
Remove GST from a price that includes GST
Divide the GST-inclusive price by 1.15 to find the exclusive amount. Subtract that amount from the inclusive price to find GST. The direct GST-component formula is inclusive price multiplied by 3/23.
Example: $230 including GST divided by 1.15 is $200 excluding GST. The GST component is $30. Simply subtracting 15% from $230 would give $195.50, which is wrong because the 15% rate applies to the exclusive base, not the inclusive total.
Work backwards from a known GST amount
When the GST amount itself is known, divide it by 0.15 to find the exclusive amount. Add the GST to obtain the inclusive total. A $30 GST amount therefore implies $200 excluding GST and $230 including GST, assuming the whole supply is standard-rated.
Keep the required taxable supply information
Inland Revenue replaced the old single-document tax-invoice requirement with broader taxable supply information rules from 1 April 2023. The information required depends on the value and type of supply.
For relevant standard-rated supplies, records may show the GST-exclusive amount, GST amount and GST-inclusive amount, or show the inclusive amount with a statement that GST is included. A calculator result is not a substitute for the seller, buyer, date, description and other information required for the transaction.
Check zero-rated and exempt supplies before using 15%
Zero-rated supplies are taxable supplies charged at 0% when the statutory requirements are met. Examples can include certain exports, some services supplied to non-residents and qualifying land transactions between registered persons.
Exempt supplies are treated differently and can include common financial services and residential renting. The correct treatment depends on facts beyond a price, so do not use the standard-rate result as a tax-classification decision.
Use a consistent rounding policy
GrowThenDraw keeps full precision in the engine and displays New Zealand dollars to cents. Accounting systems can round per line, per tax component or at document total, which can create small differences across many invoice lines.
Use the same documented policy throughout your records and confirm software or adviser treatment when cents-level matching matters. This calculator shows one transparent line calculation rather than filing a GST return.