A product rarely owes a single duty. Its base duty from the tariff schedule can be joined by one or several additional duties of Chapter 99, under Sections 301, 232, 201 or 338. They do not always simply add up: the texts of each measure, in the notes of Chapter 99, say how it combines with the others. Here are the rules that matter most.
Most duties add up
Each duty is calculated on the same customs value (or on its own quantity, for a rate per unit), and the amounts are added. A product of China on a Section 301 list owes its base duty, that list's rate and, since July 24, 2026, the Section 301 rate on all goods of China, one after the other.
Some duties exempt goods from others
A measure can leave out goods that another already covers. The Section 301 actions of 2026 on 60 economies and on Brazil do not apply to goods subject to a Section 232 duty, while the older Section 301 duties on China still do. Among the Section 232 duties, a product made of steel, aluminum and copper pays the metals duty once, not once per metal.
Some rates include the base duty
Several deals set a total rather than an addition: "15% in total" for many Section 232 goods from the European Union, Japan or South Korea, or the 10% and 12.5% of the 2026 Section 301 action for goods of the European Union, Taiwan, Japan, South Korea and Switzerland. The additional duty then tops the base duty up to that total, and adds nothing when the base duty already reaches it.
Agreements lower the base, not the rest
Claiming a trade agreement lowers the base duty to its Special rate, often free. It changes an additional duty only where that duty's own text says so: goods of Canada and Mexico entered free under the USMCA are spared the 2026 Section 301 rate, and the Section 232 duty on a qualifying vehicle falls on its non-US content only. See how trade agreements lower duties.
Three examples, calculated today
Each for goods worth $10,000, without the entry fees, calculated on 2026 HTS Revision 22.
Men's cotton T-shirts from China (6109.10.00.12)
| Duty | Heading | Amount | Share of the value |
|---|---|---|---|
| Base duty | — | $1,650.00 | 16.5% |
| Section 301: Note 52 additional duty — China | 9903.05.31 | $1,250.00 | 12.5% |
| Section 301: Products of China, heading 9903.88.15 (list 4A) | 9903.88.15 | $750.00 | 7.5% |
| Total | $3,650.00 | 36.5% |
Steel bolts from China (7318.15.20.65)
| Duty | Heading | Amount | Share of the value |
|---|---|---|---|
| Base duty | — | $0.00 | 0% |
| Section 232: Metals — 50 percent | 9903.82.02 | $5,000.00 | 50% |
| Section 301: Products of China, heading 9903.88.03 | 9903.88.03 | $2,500.00 | 25% |
| Total | $7,500.00 | 75% |
Leather footwear from Germany (6403.99.90.65)
| Duty | Heading | Amount | Share of the value |
|---|---|---|---|
| Base duty | — | $1,000.00 | 10% |
| Section 301: Note 52 additional duty — a member state of the European Union | 9903.05.39 | $0.00 | 0% |
| Total | $1,000.00 | 10% |
The T-shirts add up three duties. The bolts owe the Section 232 metals duty and a Section 301 list, but not the 2026 Section 301 rate, since their Section 232 duty exempts them from it. The footwear's base duty already reaches the European Union's 10% total, so the 2026 Section 301 rate adds nothing.
Each layer has its date
Every measure has its own start, its changes and sometimes its end, and an official action can change a measure days before the USITC writes it into the tariff. The stack is therefore always for one date of entry. The entry fees come after: they are calculated on the customs value, not on the duties.
How TariffTrust stacks them
The calculator applies every measure that concerns the code, the origin and the date, combined as their texts say, each line with its heading and its official source. The measures it examined and did not apply are listed under "Sources and details", each with its reason, such as an exemption by another measure. See how to read a TariffTrust estimate.
Updated October 30, 2026. General information as of that date, not legal or customs advice: the official texts prevail, and a licensed customs broker can confirm what applies to your goods.