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The GST amount on a price is 5% of that price, so $250 before tax carries $12.50 of GST and costs $262.50 in Alberta. In an HST province the federal and provincial parts come as one tax, so the same $250 carries $32.50 in Ontario. Here’s how to work the amount out in either direction, and what changes by province.
How do you calculate the GST amount on a price?
Multiply the price before tax by the rate. At 5% that means the price times 0.05. On a $250 invoice you get $12.50, and you add it to reach $262.50.
For a ballpark in your head, start with 10% by moving the decimal point, then halve it. On $84, 10% is $8.40 and half of that is $4.20. Close enough to know whether a bill looks right.
Going the other way is where people slip. If a receipt shows a total of $105 with GST in it, don’t take 5% of $105. That gives $5.25, which is too much. The CRA’s method is to multiply a tax-included total by 5/105, and here that gives exactly $5.00. Or divide the total by 1.05 to get the $100 price, then subtract.
The GST and HST calculator does the first job, and the reverse tax calculator does the second. Pick the province and both use the current rate.
Which rate applies where you live?
GST is 5% everywhere in Canada. Some provinces then add their own tax on top, or fold theirs into a single HST. This table follows the CRA’s rate page, as we read it in September 2026.
| Where | Federal GST or HST | Provincial tax |
|---|---|---|
| Alberta, Northwest Territories, Nunavut, Yukon | 5% GST | None |
| British Columbia | 5% GST | 7% PST |
| Manitoba | 5% GST | 7% RST |
| Saskatchewan | 5% GST | 6% PST |
| Quebec | 5% GST | 9.975% QST |
| Ontario | 13% HST | Included |
| Nova Scotia | 14% HST | Included |
| New Brunswick, Newfoundland and Labrador, Prince Edward Island | 15% HST | Included |
Nova Scotia dropped from 15% to 14% on April 1, 2025, as the CRA’s page on which GST/HST rate to charge explains. If you’re looking at an invoice from before that date, the old rate is the one that applied.
What does the same $250 cost in different provinces?
We ran one price through the calculators to show how much the province matters. All amounts are before tax.
Alberta gets $12.50 of GST and a total of $262.50. Ontario’s HST is $32.50, which makes $282.50. Nova Scotia’s is $35.00, so you pay $285.00. Manitoba is the odd one out because you pay $12.50 of GST and then $17.50 of provincial tax on top, which is $30.00 of tax and $280.00 at the till, and that’s why a single rate never tells the whole story.
Quebec works out a little differently. On $1,000 the GST is $50.00 and the QST is $99.75, and the QST is worked out on the price before tax, not on the price plus GST. The total is $1,149.75. You can check your own numbers with the GST and QST calculator.
For a purchase in British Columbia, Saskatchewan or Manitoba, use the GST and PST calculator. It applies both taxes to the price before tax.
How do you pull the tax out of a total in an HST province?
Same idea as before, with a bigger divisor. A receipt for $113.00 in Ontario includes 13% HST, so divide by 1.13. The price before tax is $100.00 and the HST is $13.00. In Nova Scotia you’d divide by 1.14, and in New Brunswick by 1.15. A few bucks of error on a small bill won’t matter, but on a $5,000 purchase it will, so do the division properly.
Where do GST amount calculations go wrong?
Rounding is the first trap. The CRA says its own calculator results can be a cent or two off a final total, and that’s normal. Businesses that invoice many lines sometimes round each line, sometimes the total, and the two can differ by a few cents. Take three items at $1.10 each. Tax on each line is 5.5 cents, which rounds to 6 cents, so the line method gives 18 cents. Tax on the $3.30 total is 16.5 cents, which rounds to 17 cents. One cent apart, and both are defensible.
Then there are items that carry no tax at all, and they catch out even careful bookkeepers who assume every line on an invoice is taxable. Some goods and services are zero-rated or exempt, and the calculators can’t know which yours are. The GST/PST tool also applies both taxes to everything, and some items, like certain food or children’s goods, are exempt from one tax but not the other. If a receipt shows less tax than the tool does, the receipt is probably right.
A third mistake is using the wrong rate for the location of the sale. Where a service or product is supplied can differ from where you live, and we haven’t covered those rules here. Check the CRA’s guidance before you charge a customer in another province.
Small suppliers don’t always have to charge GST. The CRA’s guide for GST/HST registrants sets the small supplier line at $30,000 of taxable sales in any single calendar quarter or over the last four consecutive quarters. Go over either test and you have 29 days from the sale that took you over to register.
What should a business put on an invoice?
Show the price, then the GST or HST as its own line, then the total. If you’re registered, your GST/HST number goes on it as well. Customers who claim input tax credits need to see the amount of tax, and it’s easier to give it than to answer questions about it later.
Buying a new home is a special case. The tax can be large and there are rebates, which the new housing rebate calculator estimates.
What this page is based on
The rates come from the Canada Revenue Agency‘s GST/HST rates by province page. The 5 over 105 fraction is our own arithmetic on a 5% rate. We checked the rates on September 30, 2026. Manitoba’s 7% rate comes from the province’s own retail sales tax page. This is an independent guide, separate from any government body.
Frequently asked questions
How do I find the GST amount on a total that already includes tax?
Multiply the total by 5/105 if the tax is 5% GST. A $105 receipt holds $5.00 of GST.
Is GST always 5%?
Yes, the federal rate is 5%. In HST provinces the federal and provincial parts are combined at 13%, 14% or 15%.
Is the QST charged on top of the GST?
In our calculator both are worked out on the price before tax. On $1,000 that is $50.00 GST and $99.75 QST.
Why does my receipt differ from the calculator by a cent?
The CRA says results can differ by a cent or two because of rounding. Stores round in different places.
Do I have to charge GST if I run a small business?
Not always. Small suppliers below the CRA limit can skip it, but we haven't confirmed the current limit, so check the CRA page.
- GST, HST, PST and QST explained for every province
Which GST, HST, PST or QST applies where you shop or sell in Canada, the 2026 rates for every province, who must register and how to add or remove tax