How this calculator works
GST (Goods and Services Tax) works the same way as VAT: it is a tax on the sale of goods and services, and the same add/extract arithmetic applies whether you are pricing an invoice net of tax or working out how much tax was inside a receipt total. This page defaults to Canada's federal GST rate of 5%, but the calculator works for any GST-style rate — enter your own to match your province or country.
Canada's system is more layered than a single flat rate. Some provinces harmonize the federal GST with a provincial sales tax into a single HST (Harmonized Sales Tax) rate charged as one line; others charge GST and a separate provincial sales tax (PST) side by side. Australia and New Zealand, by contrast, each apply one flat national GST rate. Treat any specific rate mentioned here as a labeled example only — confirm the current rate for your province or country before relying on it.
The formulas
Add GST: tax = net × (rate ÷ 100); gross = net + taxExtract GST: net = gross ÷ (1 + rate ÷ 100); tax = gross − netAdding tax and then extracting it at the same rate returns the original net price exactly, whether the rate represents GST alone or a combined HST rate.
Worked example: 13% HST on an Ontario-style purchase
- A service is billed at $100.00 net, in a province that charges 13% HST (the harmonized combination of federal GST and provincial tax).
- Tax: 100 × 0.13 = $13.00.
- Gross price charged to the customer: 100 + 13 = $113.00.
- In a GST-only province at 5% instead, the same $100 net service would show $5.00 tax and a $105.00 gross price — always enter the rate that actually applies where the sale happens.
Frequently asked questions
What is the difference between GST, HST, and PST?
GST is Canada's federal 5% goods and services tax. In five provinces (as commonly published examples: Ontario at 13%; New Brunswick, Newfoundland and Labrador, and Prince Edward Island at 15%; and Nova Scotia at 14% since a 2025 rate cut), GST is combined with the provincial sales tax into one HST rate charged as a single line. In other provinces, GST and a separate PST (or, in Quebec, QST) are charged side by side instead of harmonized. Combined rates and provincial rules change from time to time, so check your province's current rate before relying on a figure.
What GST rate should I enter?
Whatever combined rate actually applies to your purchase. As labeled examples: Canada's federal GST alone is 5%; combined HST reaches 13-15% depending on province; Australia charges a flat 10% GST; New Zealand charges a flat 15% GST. Always confirm the current figure for your jurisdiction rather than assuming one of these applies.
Why can't I just take the tax rate as a percentage of the total price?
Because the rate applies to the net price, not the tax-inclusive total. On a $113 gross price at 13% HST, the tax is $13 (13% of the $100 net), not $14.69 (13% of $113). Divide by 1 + rate ÷ 100 first to find the net price, then subtract to find the tax.
Do businesses need to register to charge GST/HST?
That depends on revenue and is a business decision this calculator doesn't make for you. Registration thresholds and rules are set by the Canada Revenue Agency (or the equivalent tax authority in Australia or New Zealand) and change periodically — check the current requirement before assuming you do or don't need to register.
Does this calculator work for Australian or New Zealand GST?
Yes — the underlying math is identical. Just replace the default 5% with Australia's flat 10% rate or New Zealand's flat 15% rate (or your own figure), since neither country splits GST into separate harmonized/provincial components the way Canada does.