Reverse Sales Tax Calculator: find the amount before taxes

You have a $114.98 total and need to know how much of it is GST, QST and pre-tax amount? Divide by 1.14975. Enter the total below and the calculator breaks out all three figures instantly, in your browser, with no signup.

Enter the total amount paid, taxes included.

GST included (5%)
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QST included (9.975%)
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Amount before taxes
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Rates updated on July 27, 2026 · Source: Revenu Québec

This tool is provided for information purposes only and is not a substitute for professional tax advice.

Frequently asked questions

How do I calculate the pre-tax amount from a total?

Divide the total by 1.14975. For example, $114.98 ÷ 1.14975 = $100.00 before taxes. This calculator applies the formula and breaks out the GST and QST included.

What is the reverse sales tax formula in Quebec?

GST included = total × 0.05 ÷ 1.14975. QST included = total × 0.09975 ÷ 1.14975. Pre-tax amount = total − GST − QST. Calculating the taxes first guarantees that the three amounts add up to exactly the total you entered, with no one-cent discrepancy.

Why divide by 1.14975 instead of subtracting 14.975%?

Because the percentage applies to the pre-tax amount, not to the total. Subtracting 14.975% from a $114.98 total would give $97.76, which is wrong. Division is the only exact method.

When do you need a reverse sales tax calculation?

Mostly to record a receipt that only shows a total, to check a supplier invoice, or to claim input tax credits (ITC) and input tax refunds (ITR) on an expense.

Does this work if only GST applies?

No — this calculator assumes both GST and QST apply, which is the case for most taxable supplies in Québec. For a purchase outside Québec, use the rate of the relevant province.

The reverse sales tax formula in Quebec

Starting from a total that includes GST and QST:

GST included    = total × 0.05    ÷ 1.14975
QST included    = total × 0.09975 ÷ 1.14975
Pre-tax amount  = total − GST − QST

On a $114.98 total:

LineCalculationAmount
GST included114.98 × 0.05 ÷ 1.14975$5.00
QST included114.98 × 0.09975 ÷ 1.14975$9.98
Amount before taxes114.98 − 5.00 − 9.98$100.00

Note the order: the taxes are calculated first, then the pre-tax amount is derived by subtraction. That guarantees the three lines add up to exactly the amount you entered. Doing it the other way around — dividing by 1.14975 first for the pre-tax figure, then recomputing taxes on it — can leave a one-cent gap against the starting total after rounding. On an invoice, that gap is visible and awkward.

Why divide instead of subtracting 14.975%?

This is the most common mistake. The percentage applies to the pre-tax amount, not to the total. Taking 14.975% off $114.98 would give:

114.98 − (114.98 × 0.14975) = $97.76     ← WRONG
114.98 ÷ 1.14975            = $100.00    ← EXACT

A $2.24 gap on a $100 invoice — over 2%. Repeated across a year of expenses, the error becomes material in your ITC and ITR claims.

The mental shortcut

For a quick sanity check without a calculator, remember that the pre-tax amount is roughly 87% of the total (1 ÷ 1.14975 = 0.8698). A $500 total therefore contains about $435 before taxes. That is enough to spot an odd invoice; use the calculator for the exact figure you will book.

When do you need this calculation?

  • Recording a receipt that only shows a total — restaurant, fuel, small supplies.
  • Claiming ITCs and ITRs: the refund covers the taxes paid, so they have to be isolated from the total.
  • Checking a supplier invoice: recomputed taxes do not match? The rate applied may be wrong, or a line may be zero-rated or exempt.
  • Setting a tax-included display price: start from the target total and work back to the pre-tax amount to confirm your margin.

Limits of this calculator

It assumes both GST and QST apply at the full rate. That is not always true:

  • Zero-rated supplies (0% rate): most basic groceries, certain drugs and medical devices.
  • Exempt supplies: most health services, financial services and residential rents — no tax, and no ITC available on the related inputs.
  • Purchases outside Quebec: use the HST or PST rate of the relevant province, not 1.14975.

When in doubt, trust the tax lines printed on the invoice rather than a reverse calculation.

Need the calculation the other way round? Use the GST/QST sales tax calculator.