Sales tax maths looks fiddly because Canada has thirteen different combinations of rates, but the arithmetic is the same everywhere. Once you know the combined rate for a province, three short formulas handle almost everything.
The three formulas
- Add tax: total = price × (1 + rate)
- Remove tax: price = total ÷ (1 + rate)
- Tax inside a total: tax = total × rate ÷ (1 + rate)
Write the rate as a decimal: 13% = 0.13, 14.975% = 0.14975.
1. Adding tax to a price
Multiply the pre-tax price by one plus the rate. For a $250 item:
| Where | Rate | Calculation | Total |
|---|---|---|---|
| Alberta | 5% | $250 × 1.05 | $262.50 |
| Saskatchewan | 11% | $250 × 1.11 | $277.50 |
| British Columbia | 12% | $250 × 1.12 | $280.00 |
| Ontario | 13% | $250 × 1.13 | $282.50 |
| Nova Scotia | 14% | $250 × 1.14 | $285.00 |
| Quebec | 14.975% | $250 × 1.14975 | $287.44 |
| New Brunswick | 15% | $250 × 1.15 | $287.50 |
2. Removing tax from a total
Divide the total by one plus the rate. Don't subtract the percentage from the total: the tax was calculated on the smaller pre-tax amount, so subtracting overstates it.
Example: a $339 receipt in Ontario. $339 ÷ 1.13 = $300 before tax, so the HST was $39. Subtracting 13% from $339 would give $294.93, which is wrong by more than $5.
3. Splitting a two-tax receipt
In British Columbia, Manitoba, Saskatchewan and Quebec, the GST and provincial tax are both calculated on the same pre-tax price, so you can split them once you know that price.
Example: a $114.98 total in Quebec.
- Pre-tax price: $114.98 ÷ 1.14975 = $100.00
- GST: $100.00 × 5% = $5.00
- QST: $100.00 × 9.975% = $9.98 (rounded)
Rounding
Tax is normally rounded to the nearest cent, and retailers usually calculate it on the invoice total rather than line by line. Your hand calculation may differ by a cent from a receipt. That's normal. Cash totals are also rounded to the nearest five cents since the penny was withdrawn, but tax itself is still calculated to the cent.
Common mistakes
- Using the seller's province instead of yours. For goods, the delivery province usually decides the rate.
- Stacking QST on GST. Since 2013, Quebec's QST is charged on the pre-GST price.
- Using an old Nova Scotia rate. It's been 14% since April 1, 2025.
- Taxing zero-rated items. Basic groceries and prescription drugs carry no GST or HST.
Skip the maths entirely with the calculator, which handles all thirteen jurisdictions in both directions.
Frequently asked questions
How do I find the tax rate from a receipt?
Divide the total tax by the pre-tax subtotal. A $15.60 tax on a $120 subtotal is 0.13, or 13%.
Why doesn't subtracting 13% give me the original price?
Because the tax was a percentage of the smaller pre-tax price. Removing it requires dividing by 1.13, not subtracting 13% of the larger total.
Is sales tax calculated before or after a discount?
On the discounted price. A store discount reduces the amount the tax is calculated on. A manufacturer's coupon can be handled differently.
Sources
- Canada Revenue Agency, Charge and collect the tax: which rate to charge
- Revenu Québec, GST/HST and QST