GST Calculator
Add or remove GST and HST for Canada and Australia — at any rate, in seconds.
How to use this GST calculator
Pick your currency — Canadian dollars (C$) or Australian dollars (A$) — then choose whether you want to add GST to a pre-tax price or remove GST to find the pre-tax price hidden inside a tax-inclusive total. Type your amount, set the GST or HST rate, or just tap a preset chip like “Canada GST 5%” or “Australia GST 10%”. The result updates instantly, breaking out the tax amount, the base price and the grand total.
How this is calculated
When you add GST, the calculator multiplies your amount by the rate to find the tax, then adds it on: GST = amount × rate ÷ 100 and total = amount + GST. When you remove GST from a tax-inclusive figure, it divides the total by one plus the rate to recover the pre-tax base: pre-tax = total ÷ (1 + rate ÷ 100), and the GST is whatever is left over. Rates vary by country and region and change over time, so confirm the rate that applies to your sale before relying on the figures.
Educational estimate, not tax advice — see our disclaimer.
A worked example
Say you sell a product in Australia for A$100 before tax and need to add 10% GST. The GST is A$100 × 10 ÷ 100 = A$10, so the customer pays A$110. Now flip it: a customer hands you a GST-inclusive total of A$110 and you want the pre-tax price. Divide by 1.10 to get A$100, leaving A$10 of GST. Notice you cannot simply subtract 10% of A$110 — that would give A$11, which is wrong. Removing tax always means dividing by one plus the rate, never subtracting the same percentage.
Canada vs Australia
In Canada, the federal GST is 5%. Some provinces fold the federal portion together with a provincial sales tax into a single Harmonized Sales Tax (HST) — for example 13% in Ontario or 15% in several Atlantic provinces — while others charge a separate provincial sales tax (PST or QST) on top of the 5% GST. Choose the rate that matches your province. In Australia, GST is a flat 10% applied nationwide on most goods and services, which keeps the maths simple. Whichever country you are in, set the rate to match the actual tax on your invoice.
Tips for getting it right
- Match the rate to the region — Canadian rates differ by province; Australia is a flat 10%.
- Know which direction you need — “add” starts from a pre-tax price, “remove” starts from a tax-inclusive total.
- Never subtract the percentage to strip tax — divide by one plus the rate instead.
- Rates change — governments adjust tax rates, so double-check the current figure.
Working with other tax systems? Try our VAT calculator for the UK and EU, or our sales tax calculator for the United States.