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In Québec, QST is not calculated on top of GST when a checkout uses the standard two-step method. Calculate both taxes on the taxable sale price: 5% GST and 9.975% QST. A register that calculates them together can instead apply the combined 14.975% rate to that same sale price.
Does Québec calculate QST on top of GST?
No. Under Revenu Québec’s two-step method, calculate 5% GST on the sale price, then calculate 9.975% QST on that same sale price—not on a subtotal that already includes GST. Revenu Québec describes this method on its Calculating the Taxes page.
For a $100 taxable sale, the two-step calculation is $5.00 GST plus $9.975 QST before rounding. Under Revenu Québec’s fractional-cent rule, the QST amount is ordinarily rounded to $9.98. The combined tax is $14.975 before rounding.
Which calculation method should a checkout use?
Revenu Québec describes two methods. The appropriate one depends on how the register handles tax calculations and rate precision; the guidance does not establish a universal preference between them.
#1 Best Overall
| Method | Calculation on the sale price | When it applies |
|---|---|---|
| Two-step | 5% GST, then 9.975% QST | The register calculates GST and QST separately. |
| One-step | 14.975% combined rate | The register calculates both taxes together using one rate. |
The 14.975% figure is a calculation rate for the one-step method, not a rate to print on the customer’s sale document.
How should checkout code handle precision and rounding?
Revenu Québec says only fractions equal to or greater than $0.005 must be rounded to a whole cent. It also allows taxes on multiple properties or services to be calculated on their total price before rounding the fractional amounts.
Rank #2
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- Keep sufficient precision during intermediate calculations so early rounding does not change the final amount.
- When a sale includes multiple properties or services, the taxes may be calculated on their combined price before rounding fractions.
- Use 9.975% for the two-step method and 14.975% for the one-step method when the register supports three decimal places.
Revenu Québec permits the rates to be rounded to 9.97% or 14.97% only if the register cannot process three-decimal numbers. Regardless of the method, the sale document must not show 9.97%, 14.97% or 14.975% as a tax rate.
What happens when a customer takes an early-payment discount?
For the credit-sale cash or early-payment discount scenario in Revenu Québec’s Cash Discounts guidance, calculate GST and QST on the full sale price before the discount. Its example uses a $100 purchase, $5 GST and $9.98 QST. When the customer takes a 2% discount, the taxes remain unchanged and the amount paid is $112.98.
This example concerns the described credit-sale discount. It does not establish that every coupon, rebate, trade-in or price adjustment uses the same treatment.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When does the general calculation rule need a separate check?
The two calculation methods explain how to calculate GST and QST on a sale price; they do not determine whether every transaction is taxable or what tax base applies in every case. Some special transactions have separate rules. For example, Revenu Québec’s Used Property guidance describes net-amount treatment for some used-property trade-ins and identifies an exception for road vehicles. Check the applicable transaction-specific guidance rather than extending the general calculation rule to those cases.
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Rank #4
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