No. Under Revenu Québec’s general guidance, when a register calculates Québec GST and QST separately, it applies each tax to the sale price—not QST to a price that already includes GST. A register that calculates both taxes together can instead apply the 14.975% combined rate to the sale price. Neither method means QST compounds on GST.
Choose the calculation method your register supports
Revenu Québec describes two ways to calculate GST and QST on a taxable sale. The calculation method changes how the register arrives at the tax total; it does not change the underlying sale price used for the calculation.
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| Method | Calculation | When it applies |
|---|---|---|
| Two-step | Calculate 5% GST on the sale price, then calculate 9.975% QST on that same sale price. | Use when the register calculates GST and QST in separate steps. |
| One-step | Calculate both taxes together at 14.975% of the sale price. | Use when the register calculates both taxes with one combined rate. |
These are the methods and rates in Revenu Québec’s “Calculating the Taxes” guidance. The guidance does not establish a universal preference between the methods; use the one your register can process correctly.
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Keep GST out of the QST tax base
For a $100 taxable sale using the two-step method, calculate GST as $100 × 5% = $5. Calculate QST as $100 × 9.975% = $9.975 before rounding. Do not calculate QST as 9.975% of $105: that would incorrectly feed the GST-inclusive amount into the QST calculation.
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Revenu Québec’s example rates produce combined tax of $14.975 before cent rounding. This $100 calculation is an application of the published rates, not a separate example quoted from the authority.
Handle rate precision and receipt display separately
Use the 9.975% QST rate for the two-step method and the 14.975% combined rate for the one-step method when the register can process three decimal places. Revenu Québec permits using 9.97% or 14.97%, respectively, only if the register cannot process three-decimal numbers.
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Those are calculation rates, not rates to print on the sale document. Revenu Québec says the sale document must not show 9.975%, 14.975%, 9.97% or 14.97% as a tax rate, regardless of the calculation method.
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Revenu Québec states that only fractions equal to or greater than half a cent—$0.005—must be rounded to a whole cent. On the $100 two-step example, QST of $9.975 rounds to $9.98; GST is $5.00.
If a sale includes multiple properties or services, the authority says the taxes may be calculated on their total price before rounding fractional cents. For checkout implementation, keep sufficient precision in intermediate calculations so early rounding of a component does not change the final amount.
Apply the documented cash-discount rule narrowly
For a credit sale with a cash or early-payment discount, Revenu Québec’s cash-discount example calculates GST and QST on the total sale price before the discount. In its example, a $100 purchase carries $5 GST and $9.98 QST. If the customer takes a 2% discount, those tax amounts remain unchanged and the total paid is $112.98.
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This is the rule for the described credit-sale discount scenario. Do not assume that coupons, rebates, trade-ins or other price adjustments use the same tax treatment.
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The general calculation method explains how to calculate the taxes; it does not determine whether every sale is taxable or what tax base applies to every transaction. Revenu Québec’s used-property guidance, for example, describes a net-amount treatment for some used-property trade-ins and identifies an exception for road vehicles. For motor vehicles and other specialized transactions, check the applicable transaction-specific guidance rather than extending the general rule by assumption.
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