Reverse Quebec GST/QST Calculator

Quebec's 9.975% QST rate looks like a typo until you know where it came from. Before 2013 the province charged a round 9.5% QST — but calculated it on the GST-inclusive price, a tax on a tax. On a $100.00 purchase that meant 5% GST of $5.00, then 9.5% of $105.00, which is $9.975. When Quebec de-compounded the system in 2013 and moved QST onto the same pre-tax base as GST, it set the rate at 9.975% precisely so the total burden would not move. The arithmetic that produced today's odd-looking rate is the arithmetic that keeps the combined figure at 14.975% and the reverse divisor at exactly 1.14975.

The practical consequence is that both taxes now sit on the same base, so a Quebec receipt splits cleanly. Divide the total by 1.14975 for the pre-tax price; the GST is that base × 5% and the QST is the base × 9.975%. Of the tax inside any Quebec total, roughly 33.4% is federal and 66.6% is provincial — a split you can rely on across every taxable purchase, which is not true in a PST province where exemption lists differ between the two taxes.

Quebec is administratively unique in Canada: Revenu Québec collects both the federal GST and the provincial QST. The CRA does not administer GST in Quebec. For anyone reversing a receipt to support a claim, that changes where the claim goes — the GST and QST extracted from a Quebec purchase are reported together on a combined return filed with Revenu Québec, not split across two governments.

It also changes what comes back. Unlike BC's PST, Manitoba's RST, or Saskatchewan's PST — all retail taxes that a business simply absorbs — the QST is a value-added tax. Registered businesses recover the QST through input tax refunds (ITRs), the provincial counterpart to federal input tax credits. So on a Quebec receipt, both extracted slices are potentially recoverable, and both need to be identified separately: the GST as an ITC, the QST as an ITR. A reverse calculation that stops at "total tax paid" has done half the job.

Zero-rated and exempt supplies work as they do federally — basic groceries, prescription drugs, medical devices, and feminine hygiene products are zero-rated, so those lines carry no tax to extract. Financial services are exempt with restricted QST refunds, which is a distinction worth checking before claiming an ITR on a bank or insurance invoice.

A $345.00 tax-included invoice from a Montréal supplier divides by 1.14975 to a pre-tax price of $300.07, leaving $44.93 of combined tax. That splits into $15.00 of GST and $29.93 of QST.

A registered business claims the first figure as an input tax credit and the second as an input tax refund, both on the combined return. An unregistered consumer claims neither — but the split still matters if the purchase is being expensed or reimbursed net of recoverable tax, which is the common case for Quebec businesses reimbursing employee expenses.

To back out the 14.975% sales tax from any Quebec receipt or invoice, use the standard algebraic reverse formula:

For a total of $100.00 CAD:

• Total Paid: $100.00 CAD
• Pre-Tax Base: $100.00 ÷ 1.1498 = $86.98 CAD
• Total Tax Owed: $100.00 - $86.98 = $13.02 CAD

Breakdown: GST Portion (33% of tax): $4.35 CAD | QST Portion (67% of tax): $8.68 CAD