How are Canadian duty, surtax and GST calculated on a commercial import?

In what order is a Canadian import line calculated?

Every amount on a commercial CAD line except the GST is a share of one number: the value for duty, in Canadian dollars. The GST is then charged on that value plus everything else. Written as steps, with the provision that sets each one:

Steps 2 to 5 do not compound. A 25% surtax on a line with 9.5% duty is 25% of the value, not 25% of the value plus the duty. Only the GST sees the other amounts. Section 215 of the Excise Tax Act defines the value for GST as the value for duty "whether the goods are in fact subject to duty", plus "the amount of all duties and taxes, if any, payable on the goods under the Customs Tariff, the Excise Act, 2001, the Special Import Measures Act" and other customs laws. Surtaxes and safeguard surtaxes are imposed under the Customs Tariff, and anti-dumping duty under SIMA, so all of them are in the GST base.

CBSA's own worked examples follow this order. In Customs Notice 26-23, example 3 takes a value for duty of $150, a 5% MFN rate, $34 of anti-dumping duty and a 25% surtax: duty $7.50, surtax $37.50, value for tax $229.00, GST $11.45. The surtax there is 25% of $150, not of $157.50.

Step 1: what goes into the value for duty, and which exchange rate?

The value for duty is usually the transaction value under section 48 of the Customs Act: the price paid or payable, adjusted for the items the Act adds and deducts. What counts and what does not is set out in value for duty in Canada; this page starts from the value once it is right.

Section 55 of the Customs Act says the value for duty "shall be computed in Canadian currency in accordance with regulations made under the Currency Act". Those are the Currency Exchange for Customs Valuation Regulations. Section 3 uses "the rate prevailing on the date of direct shipment to Canada", and section 5 defines that as the rate "communicated to the ports of entry by the Minister for that date". It is not the release date and not the invoice date. A line converted at the release-date rate has a different value for duty, and every amount after it moves with it.

SIMA duties use their own date: section 4 of the same regulations uses the date of sale to a Canadian importer or the date of direct shipment, whichever the Special Import Measures Regulations make applicable.

Step 2: which tariff rate applies to the line?

Section 20 of the Customs Tariff levies customs duty "at the rates set out in" the List of Tariff Provisions. Each tariff item carries an MFN rate and the preferential rates, listed by tariff treatment code (UST for the United States Tariff under CUSMA, CEUT for CETA, CPTPT for CPTPP, and so on). The rate on the line is the one for the treatment claimed and supported by proof of origin.

A trade-agreement rate changes this step only. It does not touch steps 3 to 5, and the GST in step 6 still falls on whatever those steps produce. Unclaimed preferences on past lines are covered in unclaimed CUSMA, CETA and CPTPP preference.

Steps 3 and 4: how do surtaxes and safeguards fit in?

Canada imposes surtaxes by order in council under the Customs Tariff, each with its own goods, origin test and dates. On November 11, 2026 those included the United States Surtax Order (2026), the US steel and aluminum and motor vehicle orders, the China Surtax Order (2024), the melt-and-pour order, the steel quota order, the Steel Derivative Goods Surtax Order, and two provisional safeguard orders on canned vegetables and on wood cabinets and vanities. Which one applies to a line, and which one wins when two could, is set out in why your CAD shows the wrong surtax.

For the calculation, they share three features:

• Same base. Each order sets the surtax as a percentage of the value for duty determined under sections 47 to 55 of the Customs Act.
• Separate field for safeguards. Customs Notice 26-17 says that, "unlike standard surtaxes for which surtax owing is entered in field 85 'Surtax' of the CAD, the amount of safeguard owing is entered in field 87 'Safeguard'". CBSA's notices use these numbers; Memorandum D17-1-10 numbers the same Surtax and Safeguard fields 68 and 90 in its electronic coding, and the CAD field by field explains both numberings.
• Self-calculated. Customs Notice 26-23 says that if the importer uses the self-declare option in CARM, "the amount of surtax owing must be calculated by the importer".

Step 5: how does SIMA duty enter the line?

Section 3 of the Special Import Measures Act levies anti-dumping duty equal to the margin of dumping and countervailing duty equal to the amount of subsidy, on goods covered by a Tribunal order or finding. The amount comes from the measure in force: an exporter-specific normal value, or a rate the CBSA sets for exporters without one. It sits on top of customs duty and any surtax, and goes into the GST base. Checking past SIMA lines is covered in SIMA duties on past Canadian entries.

Step 6: what does the GST fall on?

Section 212 of the Excise Tax Act charges tax "at the rate of 5% on the value of the goods", and section 215 builds that value from the value for duty plus the duties and taxes above. Customs Notice 26-23 adds two points: the value for tax "is inclusive of surtax even when customs duties are remitted", and GST "is not payable on non-taxable importations, even if the importation is subject to the surtax".

On provincial tax: section 212.1 adds a provincial component for participating provinces, but subsection 212.1(3) says the residence-based part does not apply to goods accounted for as commercial goods under section 32 of the Customs Act.

Worked line 1: wooden kitchen cabinets from China, with a safeguard

The figures are illustrative and round, and the exchange rate is an assumption. A CAD line of wooden kitchen cabinets for permanent installation, tariff item 9403.40.00, origin China, invoiced at USD 20,000 (transaction value, freight to the place of direct shipment included), released on October 20, 2026. Assume the rate communicated for the date of direct shipment is 1.3800 and that no SIMA measure applies to the goods.

• The Customs Tariff 2026, Chapter 94, lists 9403.40.00 at an MFN rate of 9.5%.
• The Certain Wood Cabinet and Vanity Goods Surtax Order applies a 25% surtax from July 31, 2026, for up to 200 days, to cabinets "made in whole or in part of wood products and intended for permanent installation". Classification number 9403.40.00.10 is in its schedule. Its exclusions cover goods originating in the US, Mexico, Chile, Israel or another CIFTA beneficiary and the developing countries in its Schedule 2; China is not among them. The CAD code is 26169A, in field 87. Under section 3 of the order, once the Canadian International Trade Tribunal submits its safeguard report the surtax applies only to the goods that report finds injurious; the Tribunal's active safeguard inquiries page lists that report for January 15, 2027, so the full order applied to this October 2026 line.

The same line entered wrong, in both directions:

• Safeguard on the duty-paid value, 25% of 30,222.00 = 7,555.50. Overpaid by 655.50, plus 32.78 of GST on it.
• GST before the safeguard was added, 5% of 30,222.00 = 1,511.10. Underpaid by 345.00 of GST.
• Safeguard in field 85 instead of field 87. The money may be right, but the line no longer matches what Customs Notice 26-17 asks for, and a reconciliation by field will not tie.
• Converted at the release-date rate. Every amount on the line moves; a one-cent difference in the rate on USD 20,000 moves the value for duty by CAD 200 and the total payable by CAD 82.45.

Worked line 2: steel screws from Chinese Taipei, with a surtax and SIMA

Again illustrative. A CAD line of carbon steel machine screws, M6 by 30 mm, tariff item 7318.15.00, from an exporter in Chinese Taipei that has not been issued its own normal values, value for duty CAD 10,000, released on October 20, 2026, not imported for motor vehicle or aerospace manufacturing. Assume the SIMA export price is also CAD 10,000; in practice it is determined under SIMA and can differ from the value for duty.

• The Customs Tariff 2026, Chapter 73, lists 7318.15.00 as free under the MFN tariff.
• 7318.15.00 is on the schedule of the Steel Derivative Goods Surtax Order, which applies a 25% surtax to every origin (Canada excepted since June 22, 2026), subject to its exceptions. Its end-use exceptions cover goods imported before July 1, 2027 for use in manufacturing motor vehicles or their parts, and for use in aircraft or spacecraft. Plain machine screws are not among the 7318.15.00 goods named in the schedules of the Steel Derivative Goods Surtax Remission Order, which since SOR/2026-227 (in force October 23, 2026) lists specific goods such as weld studs, rail bolts and bolts and screws for commercial greenhouses; check that list before treating a fastener line as owing the full surtax.
• The CBSA's fasteners measure in force covers certain carbon steel fasteners from China and Chinese Taipei, continued by the Tribunal's order of March 11, 2026, and machine screws of M3 to M10 are among the subject goods. For an exporter without its own normal values, "the anti-dumping duty is equal to 170% of the export price". Countervailing duty applies only to goods from China.

A free duty rate does not make this a cheap line. The common errors here are leaving the derivative surtax off because the screws are not Chinese, leaving the SIMA duty out of the GST base (GST short by 850.00), and missing the SIMA duty altogether because the duty rate reads "Free".

How do you check the calculation on your own CAD lines?

1. Rebuild the value for duty from the invoice and the exchange rate for the date of direct shipment, and compare it with the declared value.
2. Recompute the duty at the rate for the tariff treatment claimed, and check that proof of origin supports the treatment.
3. List every surtax and safeguard order that held the tariff item on the release date, test origin the way each order tests it, and recompute each at its rate on the value for duty. Safeguards go in field 87, other surtaxes in field 85.
4. Check SIMA exposure against the CBSA's measures in force for the product and origin.
5. Recompute the GST on the value plus everything in steps 2 to 4, and compare it line by line.
6. Sort differences by direction. Underpayments go to a correction or adjustment; overpayments to a refund adjustment. The routes and clocks are in correcting a Canadian entry.

TariffSense reads CAD/B3 lines and broker accounting exports, rebuilds each line in this order with the measures in force on its date, and flags lines where the surtax base, the GST base or the field used does not match, in either direction. Filing stays with your broker or your CARM account. You can price a single line in the duty calculator or see what a full review covers on the post-entry audit page; the CAD audit guide covers the rest of the line.

What should you do next?

Take your largest surtax or safeguard lines from the last year and recompute two numbers by hand: the surtax as a share of the value for duty alone, and the GST on the value plus duty plus surtax plus any SIMA duty. If either differs from the declared amount, widen the check to every line with the same tariff item. Confirm any correction or refund route with a licensed customs broker before you file.