If you need to quickly calculate Canadian GST and Quebec QST, this tool gives you a fast and clear breakdown. Use it to add tax to a pre-tax amount, or work backward from a tax-included total.
GST + QST Calculator (Quebec)
Default rates are set to GST 5% and QST 9.975%.
What is GST and QST?
In Quebec, many purchases include two sales taxes:
- GST (Goods and Services Tax) — federal tax, typically 5%
- QST (Quebec Sales Tax) — provincial tax, typically 9.975%
For most standard taxable goods and services, both are applied to the price before taxes. That means the combined rate is usually 14.975%.
How to use this GST QST calculator
1) Add taxes to a subtotal
Choose Add GST/QST to a subtotal, enter your pre-tax amount, then click Calculate. You will get:
- Subtotal (before taxes)
- GST amount
- QST amount
- Total including taxes
2) Extract taxes from a total
Choose Extract GST/QST from a total if you only know the final amount paid. The calculator will estimate the pre-tax subtotal and split the included taxes into GST and QST portions.
Formulas used
When adding taxes
Let S = subtotal, g = GST rate, and q = QST rate:
- GST = S × g
- QST = S × q
- Total = S + GST + QST
When extracting taxes
Let T = total (tax included):
- Subtotal = T ÷ (1 + g + q)
- GST = Subtotal × g
- QST = Subtotal × q
Rates in formulas are decimals (for example, 5% = 0.05).
Example
If your subtotal is $100.00 with GST 5% and QST 9.975%:
- GST = $5.00
- QST = $9.98 (rounded)
- Total = $114.98 (rounded)
If you start from a total of $114.98 and extract tax, the calculator estimates the original subtotal and tax components using the same rates.
Helpful tips for invoices and budgeting
- Always confirm current tax rates before issuing invoices.
- Keep pre-tax and tax amounts separated in your records.
- Round at the final invoice stage according to your accounting policy.
- For complex scenarios (exemptions, mixed supplies, refunds), confirm with a tax professional.
Frequently asked questions
Is this calculator only for Quebec?
The default setup is for Quebec (GST + QST), but you can edit the rates for other scenarios.
Does this replace professional tax advice?
No. This is a practical estimation tool for everyday calculations, not legal or accounting advice.
Why can one-cent differences happen?
Rounding rules can differ by system and invoice line method. Small cent-level differences are normal in real-world billing systems.