How to calculate US import duty when tariffs stack on one HTS line

Short answer: to calculate US import duty, take each entry line’s HTSUS (Harmonized Tariff Schedule of the United States) number, find the line’s dutiable value under 19 USC 1401a, and multiply that value by every ad valorem rate the line carries: the Column 1 General (MFN) rate plus each Chapter 99 additional duty that applies to it. Add any specific duty (rate times quantity). Each rate is applied to the same value and the results are added, and the HTS number, the country of origin and the entry date decide which rates apply at all. Then add the fees: the merchandise processing fee (MPF) of 0.3464%, held between $34.58 and $670.86 per formal entry, and the harbor maintenance fee (HMF) of 0.125% on ocean cargo.

Most bad estimates go wrong before the arithmetic starts: a subheading off by one, freight left in the value, or a Chapter 99 duty added to a line that is exempt from it. Below are the five steps, the rules on which US tariffs stack, and two hypothetical entries worked to the cent. Rates, dates and Chapter 99 numbers were checked on October 23, 2026 against CBP CSMS messages 69326983, 68855869 and 67844987, Proclamations 11021 and 11032, USTR’s July 2026 forced-labor notice, CBP Dec. 26-14 and the eCFR. Confirm current figures in the HTSUS (hts.usitc.gov) and CBP’s CSMS messages before you file.

What is the duty formula?

For each entry line, duty equals the line’s value times the sum of its ad valorem rates, plus the line’s quantity times any specific rate. Written out:

Line duty = (value x (Column 1 ad valorem rate + each Chapter 99 ad valorem rate)) + (quantity x specific rate)

Duty is calculated line by line. Each line of an entry summary (CBP Form 7501) has its own HTS number, value and quantity, so a 40-line entry is 40 small calculations added together. MPF is the exception: it is figured on the whole formal entry and then held between the minimum and maximum.

Which duty layers can sit on one HTS line?

As of October 2026, five duty layers and two fees can attach to a single entry summary line, each keyed to something different.

Two layers are history and should not appear on new entries. CBP stopped collecting IEEPA duties on goods entered from February 24, 2026, after the Supreme Court held that IEEPA does not authorize tariffs, and the 10% Section 122 surcharge (9903.03.01) ran from February 24 to July 24, 2026, then expired at its 150-day limit. A 25% Section 301 duty on certain Brazilian goods works like the actions below. Not every new action carries a rate: the wind turbine proclamation of October 22, 2026 opens negotiations and leaves the metals duties as they are.

Step 1: Why does the HTS code come first?

The HTS code comes first because almost every program writes its scope in HTS terms (AD/CVD is the exception, covered below). The 8-digit subheading fixes the Column 1 rate, and the 10-digit number fixes the unit of quantity. The metals proclamation lists covered subheadings in annexes carried into U.S. note 16 to subchapter III of Chapter 99; the China Section 301 lists name 8-digit subheadings in U.S. note 20; the forced-labor action exempts named subheadings through U.S. note 52. A move from a steel-tube heading in Chapter 73 to a machinery heading in Chapter 84, or from one 8-digit subheading to its neighbor, can add a 50% Section 232 duty, remove a 12.5% forced-labor duty, or move a product from a 25% Section 301 list to a 7.5% one.

A household electric rice cooker shows how close the choice can be. Heading 8516 covers “other electrothermic appliances of a kind used for domestic purposes”, and two subheadings compete: 8516.60 (“Other ovens; cooking stoves, ranges, cooking plates, boiling rings, grillers and roasters”, with US line 8516.60.40 for cooking stoves, ranges and ovens) and the residual 8516.79. In a headquarters protest decision on steam-type countertop rice cookers, CBP held that they are not ovens and not in the same class as cooking stoves and ranges, so they go to 8516.79.00. A multi-cooker that bakes or roasts may reopen the question.

That 8516.60 versus 8516.79 decision is made at the sixth digit, and it is the part TariffWolf works on. It returns the 6-digit HS subheading with the GRIs applied, the Section and Chapter notes and the CBP rulings behind it, asks about heating method and functions when a description is too thin, and leaves the last four digits of the US line to your classifier or customs broker.

Step 2: What value is duty charged on?

Under 19 USC 1401a, US duty is charged on transaction value, which starts from the “price actually paid or payable” in the export sale and adds certain costs. The statute excludes international transportation, insurance and related services from that price, so the US does not simply use “FOB” or “CIF”. Start from what the buyer pays the seller, take out identified international freight and insurance, and add these if they are not already in the price:

• packing costs incurred by the buyer
• selling commissions incurred by the buyer
• the apportioned value of any assist (molds, tools, materials or design work the buyer supplies free or at reduced cost)
• royalties or license fees the buyer must pay as a condition of the sale
• proceeds of any later resale that accrue to the seller

Post-importation costs that are identified separately (US assembly, inland freight after arrival, US duties and certain taxes) stay out. When buyer and seller are related, or the buyer supplies assists, the value needs more work. Value is also a line-level figure. If an assist or a packing charge is invoiced once for a whole shipment, apportion it to the lines it relates to before you apply each line’s rates.

Step 3: How do you apply each rate type?

The Column 1 rate is written in one of three forms, and each needs a different input.

A specific rate needs the quantity in the rate’s unit: if the rate is per kilogram, you need net kilograms even when the line reports “No.” A “Free” Column 1 rate says nothing about Section 232 or 301, which are charged on value whatever the MFN rate is.

Step 4: Which Chapter 99 layers stack, and which exclude each other?

Tariff stacking is the set of rules that decides which additional duties are charged together on one line. Each has its own Chapter 99 number and, when ad valorem, is multiplied by the same line value. The pairings below decide most stacks as of October 2026: “stacks” means both duties are charged and added, “excludes” means one program’s text switches the other off.

The 2024 review row is the one most often misread. The September 2024 notice raised the Section 301 rate on named lines (electric vehicles to 100%, semiconductors to 50% from 2025, non-EV lithium-ion batteries to 25% from 2026 and others), and the new rate takes the place of the list rate. A hypothetical line that paid 7.5% under List 4A and now falls under a 25% review heading pays 25%, not 32.5%, plus the 12.5% forced-labor duty.

The net-of-MFN rule also needs care. For goods of the EU and Taiwan, the forced-labor duty tops the Column 1 rate up to a combined 10% and is zero if the Column 1 rate is already 10% or more; USTR’s own example is a 4% MFN item that pays 6%. Japan, Korea and Switzerland work the same way at 12.5%. CBP gives each of them two headings, so the EU uses 9903.05.38 (Column 1 rate of 10% or more) or 9903.05.39 (below 10%). Our table of 9903.05 headings by origin country lists the rest.

A hypothetical German machine entered at $200,000 with a 2.5% Column 1 rate shows both rules. In no metals annex, it pays $5,000 MFN plus 7.5% under 9903.05.39 ($15,000): $20,000. In Annex I-B, it pays $5,000 MFN plus 25% Section 232 on the full $200,000 ($50,000) and no forced-labor duty: $55,000, however small the steel content. Machinery has two more outcomes. Certain industrial and grid equipment in Annex III pays the Section 232 rate that brings Column 1 plus Section 232 to 15% through December 31, 2027. And Proclamation 11032, effective June 8, 2026, added an Annex I-C whose aluminum and steel articles pay 25%, or a combined 15% for products of the EU, Japan, Korea, Switzerland, the UK and several other partners, through 2027.

The reporting order is fixed as well. CSMS 69326983 has filers report any Chapter 98 number first, then the Chapter 99 number for Section 301, then the other Chapter 99 numbers such as Section 232, and last the Chapter 1 to 97 number, which carries the entered value. To build the stack for one line, check in this order:

1. Origin under CBP’s rules (substantial transformation, or the agreement’s rules for a preference claim).
2. Section 232: the annex and origin rate for the subheading, and whether the vehicle and metals programs exclude each other for it.
3. For Chinese goods, U.S. note 20 for the list, U.S. note 31 for a review rate that replaces it, and any exclusion under 9903.88.69 or 9903.88.70 (the 178 exclusions are scheduled to expire on November 9, 2026).
4. The origin’s forced-labor heading, then every exemption: Section 232 coverage, the note 52 lists, USMCA and country-specific headings.
5. The scope of any AD/CVD order on the product and country.

Step 5: How are MPF and HMF calculated?

MPF on a formal entry is 0.3464% of the value of the merchandise, subject to a minimum and maximum per entry that CBP adjusts every fiscal year. From October 1, 2026 (FY2027, CBP Dec. 26-14) the minimum is $34.58 and the maximum is $670.86. The minimum bites below about $9,983 of value and the cap above about $193,666. Informal entries pay a flat fee instead: $2.77 for an automated informal entry not prepared by CBP. Goods originating under USMCA and most other US free trade agreements are exempt from MPF under 19 CFR 24.23(c).

HMF is 0.125% of the value of commercial cargo unloaded from a vessel at a port covered by 19 CFR 24.24. It does not apply to air or truck shipments, and import shipments eligible for informal entry are exempt. Unlike MPF, HMF has no cap. Freight, insurance, brokerage and inland costs belong in landed cost, not in the duty calculation.

Worked example 1: a rice cooker entry, two codes, two answers

This entry is hypothetical; every figure is invented except the MPF and HMF rates and the 12.5% forced-labor rate for China. An importer brings in 1,600 countertop rice cookers made in China by ocean on one formal entry. The invoice shows a CIF price of $19,810 (goods $18,400, ocean freight $1,350, insurance $60, each identified), and the importer gave the factory, free, a $2,000 lid mold expected to make 8,000 units.

1. Start from the invoice: $19,810.
2. Deduct the identified international freight and insurance: $19,810 – $1,350 – $60 = $18,400.
3. Add the assist, apportioned per unit: $2,000 / 8,000 units = $0.25 each; $0.25 x 1,600 = $400.
4. Transaction value: $18,400 + $400 = $18,800.

Assume Column 1 rates of 2.7% for 8516.79.00 and 4% for 8516.60.40, and no Section 301 list duty on either line. That is not a statement about the real lines; many Chinese lines do carry a list duty, so check U.S. note 20. The third column is a what-if: the line listed in Annex I-B of the metals proclamation at 25%.

MPF of $65.12 is inside the limits, so it stands. On this one entry the classification moves the bill by $244.40, and if the losing code also sat in a Section 232 annex the gap would be $2,594.40. Across 52 weekly entries of the same size, the $244.40 gap becomes $12,708.80. Following CBP’s position on these cookers, the right line is 8516.79.00 and the duty is $2,857.60.

Worked example 2: a steel tube from China, and what reclassification changes

Take a hypothetical entry of welded steel tube from China, customs value $50,000, shipped by ocean. For the example, assume its Chapter 73 subheading has a free Column 1 rate, appears in Annex I-A of Proclamation 11021 (50%) and is on Section 301 List 3 (25%). Since April 6, 2026 the metals duty applies to “the full customs value of the imported product, regardless of metal content”, so there is no steel-content calculation.

Now change one fact. Suppose the tube is imported cut, bent and fitted with brackets as a dedicated part of a machine, and the GRIs place it in a Chapter 84 parts subheading that is not in any metals annex. The 50% layer disappears, 12.5% under 9903.05.31 comes on because the Section 232 exemption no longer applies, and the Section 301 rate becomes whatever list (if any) that subheading is on. The reclassification has to follow from the product facts and the notes; a heading chosen to escape a duty is a misclassification.

How does AD/CVD fit into the calculation?

AD/CVD is a separate layer that the HTS code does not decide. Each Commerce order’s scope is a written product description, and under 19 CFR 351.225 Commerce reads scope questions from that language and, where needed, the petition, earlier scope rulings and the ITC’s determinations. The HTS numbers in an order help CBP flag entries, but a product can be in scope under an unlisted number. Chinese pipe and tube is the standard case: in worked example 2, an in-scope tube would carry the AD and CVD cash deposits for its producer and exporter on top of the $37,500.

Which calculation mistakes come up most?

These errors recur in duty estimates:

• Taking a supplier’s code, or a 6-digit code, and assuming the US 10-digit line, its rate and its Chapter 99 exposure without checking the notes.
• Leaving international freight and insurance in the value, or forgetting an assist, packing or royalty that belongs in it.
• Compounding rates (applying 12.5% to a value that already includes the MFN duty) instead of applying each rate to the same value.
• Applying a specific rate to the wrong unit, for example gross weight instead of net, or pieces instead of kilograms.
• Calculating MPF per line, or charging HMF on air freight.
• Keeping IEEPA or Section 122 in the spreadsheet, adding the forced-labor duty to a Section 232 line, or adding a 2024 review rate on top of the list rate it replaced.
• Charging metals duty on steel content only, a method that ended on April 6, 2026.

Related reading

• How to classify a product from description to HTS code
• Section 301 China tariffs: lists, rates, exclusions and how to lower the duty
• The 100,000-Line Problem That Followed Me for Eight Years
• The Most Reliable Tariff Classification Workflows in 2026

Frequently asked questions

How do you calculate import duty when several tariffs apply to one line?

Multiply each ad valorem rate (the Column 1 rate and every Chapter 99 duty that applies) by the same customs value and add the amounts; the rates do not compound. A 2.7% MFN rate and a 12.5% additional duty on $10,000 give $270 plus $1,250, or $1,520. Then add MPF and HMF, which are fees calculated separately.

Is US import duty calculated on FOB or CIF value?

Neither, strictly. The US uses transaction value under 19 USC 1401a: the price paid or payable for the goods, excluding international freight and insurance, plus additions such as assists, packing, commissions and royalties. In practice that often lands near the FOB price, but the additions can push it higher.

Do Section 232 and Section 301 tariffs stack?

Yes, for Chinese goods covered by both, the Section 232 duty and the China Section 301 list or review rate are both charged and added. The 2026 forced-labor Section 301 duty is different: as of October 2026 Chinese goods pay it at 12.5% on top of the China Section 301 rate, but goods subject to the Section 232 metals, vehicle, wood or semiconductor duties are exempt from it under 9903.05.90.

What are MPF and HMF, and how much are they?

They are user fees, not duties. As of October 2026 (fiscal year 2027), MPF on a formal entry is 0.3464% of the entry’s value, but never less than $34.58 or more than $670.86, and CBP resets those limits each October 1. HMF is 0.125% of the value of cargo unloaded from a commercial vessel, with no cap; air and truck shipments do not pay it.

When a new tariff action is announced, the method stays the same: read which HTS lines it covers, what it excludes and how it is reported, and run the line again.

If you are re-checking duty across a catalog, TariffWolf’s bulk classification service takes your SKU list through its web interface or a Google Sheets or Excel add-on and hands back each product’s 6-digit HS code with the notes, GRIs and CBP rulings that support it, so your classifier or broker can pick the 10-digit line and its Chapter 99 layers from a documented base. Send a sample of SKUs and read the justifications before you build a duty model on them.

Sources

• 19 USC 1401a, Value (transaction value)
• 19 CFR 24.23, Merchandise processing fee and CBP Dec. 26-14, Customs user fees for fiscal year 2027, 91 FR 48398 (July 31, 2026)
• 19 CFR 24.24, Harbor maintenance fee
• CBP CSMS 69326983 on the forced-labor Section 301 duties (July 23, 2026) and the presidential memorandum, 91 FR 47717 (July 28, 2026)
• Proclamation 11021, 91 FR 18201 (April 9, 2026), Proclamation 11032, 91 FR 34085 (June 4, 2026) and CBP CSMS 68855869
• USTR, Section 301 four-year review modifications, 89 FR 76581 (September 18, 2024) and CBP CSMS 62411889
• Congressional Research Service, IN12545, Section 232 auto tariffs (May 11, 2026)
• 19 CFR 351.225, Scope rulings
• Census Bureau, 2026 Schedule B, Chapter 85 (heading 8516 text)