If you’ve ever stared at a receipt wondering how the tax numbers actually add up, you’re not alone. Quebec’s dual tax system — GST (TPS) plus QST (TVQ) — catches plenty of people off guard, especially when the math doesn’t work the way most calculators assume. Below is a step-by-step guide that walks through the exact formulas, shows where rounding kicks in, and explains what changes when discounts enter the picture. By the end, you’ll know exactly how to work backwards from a final price too.

4 related posts

TPS Rate (Quebec): 5% · TVQ Rate (Quebec): 9.975% · Standard VAT (France): 20% · Income Tax Bands (Ireland): 20% / 40%

Quick snapshot

1Confirmed facts
2What’s unclear
  • 2026 Irish budget adjustments to income tax bands may shift thresholds — this depends on Irish government policy decisions not yet announced
  • Full list of QST exemptions beyond groceries and baby items requires verification from Revenu Québec official guidance
  • Detailed FPZ-500 filing nuances for mixed-rate businesses — complexity varies by business type
3Timeline signal
4What happens next
  • Quebec rates remain stable; no announced changes to TPS or TVQ — businesses can plan with current rates
  • Businesses should verify SAAQ valuations for used vehicle purchases post-2025 — the 14-year rule requires updated valuation checks

The following table summarizes current tax rates and structures across jurisdictions covered in this guide.

Tax / Region Rate / Structure Source
TPS (Quebec GST) 5% on most goods Revenu Québec official rules
TVQ (Quebec QST) 9.975% on subtotal + TPS Revenu Québec calculation guide
Irish Standard Rate 20% up to €42,000 Revenu Québec official rules
French Impôt Tranches Progressive 0–45% Revenu Québec official rules

How do you calculate taxes?

Every sales tax calculation starts with the same logic: multiply the pre-tax price by the rate, then divide by 100. Quebec complicates things slightly because it applies two separate taxes sequentially rather than a single harmonized rate.

Basic formula

The foundational equation for any single tax is straightforward:

Formula

Tax amount = Pre-tax price × Rate ÷ 100

For Quebec’s GST, that means taking your sale price and multiplying by 0.05. For QST, you multiply the subtotal (price after GST) by 0.09975.

Step-by-step process

  • Start with the pre-tax sale price.
  • Calculate GST: Pre-tax price × 5%.
  • Add GST to get the subtotal.
  • Calculate QST on that subtotal: Subtotal × 9.975%.
  • Round any fraction of $0.005 or more up to the nearest cent.
  • Add both taxes to the pre-tax price for the final total.

The implication: because QST applies to the price including GST, you cannot simply stack the two rates (5% + 9.975% = 14.975%) and multiply the pre-tax price directly — that slightly overstates the final amount. Revenu Québec confirms the QST must be calculated on the subtotal after GST is added.

How to calculate TPS and TVQ taxes?

Quebec differs from provinces using HST (Harmonized Sales Tax) by keeping GST and QST separate. This creates two accepted calculation methods depending on your cash register setup.

TPS first then TVQ

In the two-step method, your register calculates GST first, adds it to the price, then applies QST to that new subtotal. Revenu Québec specifies that you must use the 9.975% rate for QST when using this approach.

Example

On a $100 sale: GST = $5.00. Subtotal = $105.00. QST = $105.00 × 0.09975 = $10.47 (rounded). Total = $115.47.

2021 rates reference

Rates have remained stable since 2013 when QST was set to 9.975% and the calculation methodology shifted so QST applies to the original price, not the price plus GST. The combined effective rate works out to approximately 14.975% when calculated correctly.

What this means: if your cash register cannot handle three decimal places, Revenu Québec allows rounding to 9.97% and 14.97% internally — however, these rounded figures must not appear on any sale documents.

What is the formula to calculate taxes?

Beyond the standard forward calculation, tax formulas also cover reverse-engineering the pre-tax price from a final total and accounting for compound application.

Percentage formula

Compound formula

Total = Pre-tax price × (1 + 0.05) × (1 + 0.09975)
Total = Pre-tax price × 1.14975

For a single tax, the standard percentage formula holds: Amount = Price × (Rate ÷ 100). TaxCloud provides the QST formula as QST = Sales Amount × 0.09975, rounded to the nearest cent.

Reverse calculation

When you have the final price and need to work backwards, Omni Calculator provides the reverse formula:

Reverse formula

Pre-tax = Post-tax ÷ (1 + 0.05 + 0.09975)
Pre-tax = Post-tax ÷ 1.14975

This becomes useful when you receive an invoice with tax already included and need to verify the base amount or claim input tax credits.

How to calculate taxes and discounts?

Discounts complicate the calculation because the order of operations matters. Apply the discount before calculating tax, not after.

Order of operations

  • Take the original list price.
  • Subtract any discounts or rebates.
  • Calculate GST on the reduced price.
  • Calculate QST on the subtotal after GST.

The catch: if you apply a discount after tax, you effectively refund less money than the customer expects — the tax portion gets calculated on the full pre-discount total. Quebec’s rules require the discount be applied to the pre-tax price first.

Rabais before taxes

In French business practice, “rabais avant taxes” (discount before tax) is the standard approach. TaxCloud confirms the calculation sequence: discount first, then GST at 5%, then QST at 9.975% on the discounted subtotal.

The trade-off: while this method benefits the buyer by reducing the tax burden proportionally, it requires careful record-keeping to demonstrate the discount was applied pre-tax in case of an audit.

How to calculate TPS from the total?

Extracting the TPS component from a final bill is essentially the reverse calculation problem applied to a specific tax tier.

Reverse TPS formula

Reverse TPS

Pre-tax = Total ÷ 1.05
TPS extracted = Total − Pre-tax

Because TPS is the first layer in Quebec’s compound system, you can isolate it by dividing the subtotal (after TPS but before QST) by 1.05.

Tools and calculators

Several tools help ensure compliant calculations. Omni Calculator offers a free GST/QST calculator that handles the compound math automatically. MWM’s Québec TPS TVQ app is designed specifically to adhere to Quebec’s regulatory requirements. Bankeo notes that businesses report GST/QST via form FPZ-500, declaring collected taxes and net payable.

For frequent transactions, automated tools reduce rounding errors and ensure consistency. For occasional calculations or verification purposes, the manual formulas above work reliably.

Bottom line: Quebec’s two-step tax system (5% GST + 9.975% QST) requires calculating GST first, then applying QST to the subtotal. Quebec-based businesses that qualify for the Quick Method can reduce their GST remittance to 1.8% or 3.6% of taxable sales, simplifying compliance for eligible vendors. Businesses should always apply discounts before tax, use rounded figures only internally (never on receipts), and verify SAAQ valuations for used vehicles under 15 years old as of 2025.

Confirmed facts

  • TPS at 5% and TVQ at 9.975% apply to most goods and services in Quebec
  • QST rate set to 9.975% since 2013 on original price, not on price plus GST
  • SAAQ estimated value rule applies to vehicles 14 years old or less as of January 1, 2025
  • Rounding: fractions of $0.005 or greater round up to the nearest cent

What’s uncertain

  • 2026 Irish budget changes to income tax thresholds are not yet confirmed
  • Complete QST exemption list beyond groceries and baby items requires further verification
  • Detailed FPZ-500 filing nuances for businesses with mixed rate categories

You must use the 9.975% rate to calculate the QST if your cash register calculates the GST and QST in two steps.

— Revenu Québec (Official Tax Authority)

Since 2013, QST (9.975%) is calculated on the original price, NOT on (price + GST).

— WOWA.ca (Financial Calculator Site)

Related reading: Registraire des Entreprises Mon Dossier – Guide to REQ Access · Royal Bank Stock TSX – Price, Dividend and Performance Guide

Additional sources

omnicalculator.com, mwm.ai, apps.apple.com, taxcloud.com, apps.apple.com, en.bankeo.ca, revenuquebec.ca

For comparisons across Canadian provinces, the Ontario salary after-tax calculator breaks down 2025 CRA brackets alongside provincial rates for precise take-home pay estimates.

Don't miss these

Frequently asked questions

What order to apply discounts and taxes?

Always apply discounts to the pre-tax price first. Calculate GST on the reduced amount, then QST on the GST-inclusive subtotal. This approach ensures the customer receives the full benefit of the discount and keeps your records consistent with Revenu Québec guidelines.

How does property tax differ from sales tax?

Property tax (like France’s Impôt Foncier) is assessed on real estate value by local municipalities and uses progressive rate bands, whereas sales tax applies to individual transactions at a flat or compound percentage. Quebec’s TPS/TVQ system applies to goods and services at the point of sale, not property ownership.

Are there online calculators for TPS/TVQ?

Yes. Omni Calculator offers a free GST/QST tool that handles both forward and reverse calculations. MWM’s Québec TPS TVQ app is designed specifically for Quebec compliance. Both handle the compound calculation correctly, unlike many generic calculators that simply stack the rates.

What if taxes are compounded?

Quebec’s system is inherently compound because QST applies to the price after GST is added. The effective combined rate is approximately 14.975%, not 14.975% as a simple sum. If you’re calculating manually, ensure you add GST first, then apply QST to that subtotal — never multiply the pre-tax price directly by 14.975%.

How to verify tax calculations?

Cross-check using the reverse formula: divide the total by 1.14975 to get the pre-tax amount, then multiply by 0.05 to verify GST and by 0.09975 to verify QST. Revenu Québec also recommends keeping detailed transaction logs and reconciling against form FPZ-500 filings quarterly.

Differences between TPS and TVQ?

TPS (Taxe de Vente du Québec / QST) is the federal GST collected by the Canada Revenue Agency. TVQ is the Quebec provincial sales tax collected by Revenu Québec. Quebec is the only province that maintains these as separate taxes rather than harmonizing them into a single HST rate like Ontario or Nova Scotia.

Can I calculate income tax the same way?

No. Income tax (like Ireland’s PAYE system or France’s Impôt sur le Revenu) uses progressive marginal bands based on annual income, not a flat percentage applied to individual transactions. Quebec’s TPS/TVQ are consumption taxes on purchases, while income tax is assessed on earnings and reported annually.