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Calculating GST or QST on Their Own

In Quebec, GST and QST aren't a single combined 14.975% tax: they're two separate calculations that can each be done, quoted and reported on their own. Here's how to isolate either one, with worked examples.

Hand signing a form with columns of amounts, like a GST and QST return

Nothing changes in the method: each tax remains a percentage of the price before tax, applied independently of the other. The federal GST is 5%; Quebec's QST is 9.975%. Neither depends on the amount of the other: QST isn't calculated on GST, and vice versa, since the 2013 reform.

Diagram showing GST at 5% and QST at 9.975% calculated independently on the same price before tax, neither applied on top of the other

The Formula for a Single Tax

Tax amount = price before tax × that tax's rate

It's exactly the same operation as calculating both taxes together, except you stop after one multiplication instead of two. No conversion or rate adjustment is needed.

Example: a service billed at $850.00 before tax, in Quebec

Price before tax $850.00
GST only5% $42.50
QST only9.975% $84.79
TOTAL (both) $977.29

$850.00 × 5% gives $42.50 of GST. $850.00 × 9.975% gives $84.7875, rounded to $84.79 of QST. Each result stands on its own: to report “GST collected: $42.50” on a return, the first line is all you need, without touching the second.

Calculation receipt with the QST line highlighted, separate from the GST line, to show it can be quoted on its own

Why Isolate a Single Tax

  • GST and QST returns. A registrant files two returns, a federal one for GST and a provincial one for QST, each with its own amount of tax collected over the same period. Each tax calculation has to stay separate to fill out both forms correctly.
  • A purchase outside Quebec. A Quebec business buying in person from a supplier in Alberta pays only GST (5%) on that specific purchase, with no QST: you then need to calculate GST alone for that item, even if the business charges both taxes to its own customers.
  • A partial tax credit. Some input tax credits or rebates cover only one of the two taxes; isolating the exact amount of that tax avoids an incorrect claim.

Isolating a Tax in a PST Province

The same principle applies in British Columbia, Manitoba and Saskatchewan, where GST (5%) and the provincial tax (PST or RST, 6% or 7% depending on the province) are also two separate calculations on the price before tax. On a $400.00 purchase in British Columbia, GST alone gives $20.00 and PST alone gives $28.00; the difference from Quebec is the rate of the second tax, not the method.

Do the Calculation Automatically

The sales tax calculator already shows each tax on its own line (GST, QST, HST or PST depending on the province chosen), so there's no need to isolate them by hand. For the full formula for both taxes together and the QST detail, see the sales tax guide.

Calculate my sales tax

Sources

Article provided for informational purposes, current with the rates in effect in 2026. CalculatriceTaxes.ca is an independent site, not affiliated with the Canada Revenue Agency or Revenu Québec.