Adding versus removing GST
GST (Goods and Services Tax) is a percentage added to the price of most goods and services. The maths depends on whether your starting figure already includes the tax:
The common mistake is "removing" GST by simply subtracting the rate — taking 10% off a GST-inclusive $110 gives $99, which is wrong. Because the 10% was added to the smaller net figure, you must divide by 1.10, giving a net of $100 and $10 of GST.
Worked example
A product is listed at $110 including 10% GST. What was the price before tax?
GST & VAT rates around the world
"GST" and "VAT" are the same idea under different names. This calculator works with any rate; common standard rates as of 2026 include:
| Country | Tax name | Standard rate |
|---|---|---|
| Australia | GST | 10% |
| New Zealand | GST | 15% |
| Singapore | GST | 9% |
| India | GST (slabs) | 5% / 12% / 18% / 28% |
| Canada | GST (+ provincial) | 5% federal (HST up to 15%) |
| United Kingdom | VAT | 20% |
Rates and the items they apply to are set by each tax authority and change periodically; confirm the current rate with your local revenue agency before issuing an invoice. The United States, notably, uses sales tax (added at checkout, varying by state and city) rather than a national GST/VAT — for that, use the sales tax calculator.
Rounding and invoicing notes
- Round at the end, on the tax line. Most tax authorities expect GST shown to the cent on the invoice. Calculate the exact figure, then round the displayed tax to two decimals.
- Per-line vs invoice-total rounding can differ by a cent on multi-item invoices. Pick one method and apply it consistently; many systems compute GST on the invoice subtotal.
- Registration thresholds matter. Businesses below a turnover threshold may not charge GST at all. Whether you must register is a rule of your jurisdiction, not a calculation.