Choose the jurisdiction before calculating
New Zealand Inland Revenue describes a 15% GST standard-rate calculation for most taxable supplies by registered businesses. IRAS states Singapore’s current standard rate is 9%, subject to its zero-rated and exempt categories. These are separate systems, despite both using the label GST.
A standard-rate calculator performs arithmetic for one amount. It does not decide registration status, classification, place of supply, input-tax eligibility or the contents of a return. Verify those questions using the relevant official guidance and actual transaction records.
Compare two equal base prices, not two exchange rates
For a fictional NZD 100 base at 15%, GST is NZD 15 and the inclusive total is NZD 115. The included amount can be recovered as 115 × 15/115 = 15; Inland Revenue also expresses this fraction as 3/23.
For a separate fictional SGD 100 base at 9%, GST is SGD 9 and the inclusive total is SGD 109. Included GST is 109 × 9/109 = 9. The table compares arithmetic in two different currencies. It makes no currency conversion or claim that the underlying purchases have equal purchasing power.
Reconcile the result with the invoice
Confirm whether discounts, delivery or other charges belong in the taxable base for the actual supply. Do not use an inclusive total as the exclusive input and add GST again. Differences can also arise when a full invoice rounds individual lines rather than one aggregate amount.
Numbriv’s country-specific tools show their scope and exclusions before reliance. The examples are not invoices and do not reproduce every return adjustment. For Australia, use the separate Australia GST tool and its own official source rather than carrying either of these rates across borders.
Worked example
| Item | Illustration |
|---|---|
| New Zealand: separate base | NZD 100.00 |
| New Zealand: GST / inclusive total | NZD 15.00 / 115.00 |
| New Zealand included fraction | 15/115 = 3/23 |
| Singapore: separate base | SGD 100.00 |
| Singapore: GST / inclusive total | SGD 9.00 / 109.00 |
Try the relevant tools
Use each calculator only for its displayed jurisdiction and assumptions. Choose your country and check available coverage.
Common questions
Does GST always use the same rate worldwide?
No. Use the relevant jurisdiction, supply treatment and current official guidance.
Is this a foreign-exchange comparison?
No. Each example uses its own currency and an invented base price; no exchange rate is supplied.
Sources and editorial responsibility
Official references checked October 21, 2026 for the background described in this guide. Fictional amounts and scenario arithmetic are Numbriv illustrations, not market data or official reference cases.
Calculation methodology · Report a correction · Financial disclaimer. No licensed professional review is claimed.