How US Import Duties Stack: MFN + Section 301 + Section 232
The base duty rate on your customs entry is just the beginning. Additional tariffs from multiple authorities can stack to 50%, 80%, or even 130%+ on certain products from certain countries.
The layers
US import duties are not a single rate. They're built from multiple independent authorities, each adding their own percentage:
| Layer | Authority | Typical range | Applies to |
|---|---|---|---|
| MFN rate | USITC HTS Schedule | 0-25% | All countries (base rate) |
| Section 301 | USTR (Trade Act 1974) | +7.5% or +25% | China only |
| Section 232 | Commerce Dept | +25% | Steel/aluminum from most countries |
| Reciprocal tariffs | Various | +10% to +50% | Country-specific |
| AD/CVD | Commerce/ITC | Varies widely | Specific products from specific countries |
These rates are additive. Each layer is calculated on the entered value of the goods and added to the total duty owed.
Real examples
Each example shows two numbers. Schedule rate + Section 301 is from the USITC schedule on 2026-10-03: the base rate plus Section 301 when the code is on USITC's China Tariffs table (July 28, 2026); the other Chapter 99 lines that name the country are not added. Paid is the US Census Bureau figure for July 2026: duty collected over dutiable value on entries from that country that paid Chapter 99 duties (all dutiable entries when none did), for the 6-digit subheading. Neither is a quote for your shipment.
Example 1: Steel plate from China
The base rate is "Free"; Section 301 alone adds 25 points, and Section 232 on steel stacks on top. Census had too little recent trade in steel plate from China for a paid rate. On steel fasteners from China (7318.15.20, also Free plus 25% Section 301), importers paid 77.1% in July 2026. An importer looking only at the MFN rate would miss all of it.
Example 2: Surgical face masks from China
Face masks from China were hit by several tariff actions. Which Chapter 99 lines apply to a given mask depends on its 10-digit line and the U.S. notes to Chapter 99. An importer looking at the MFN rate of 7% would budget $700 on a $10,000 shipment. Importers of 6307.90 from China paid 21.9% in July 2026: about $2,190 on $10,000.
Example 3: Cotton t-shirt from China
Example 4: Cotton t-shirt from Vietnam
Same product, different origin: from the schedule, 24.0% from China against 16.5% from Vietnam; paid in July 2026, 33.5% against 26.7%. Both paid figures run about 10 points over the schedule figures, so the gap between the two origins held at about 7 points.
Example 5: Cotton t-shirt from Mexico (USMCA)
With USMCA rules of origin met, the MFN rate is replaced by the preferential rate (Free, in the schedule's special column). Entries from Mexico that did not claim it paid 19.9% in July 2026 (Census, dutiable entries).
Section 301: China tariffs
Section 301 tariffs apply exclusively to goods from China. Four "Lists" cover different product categories at different rates. See the full lookup tool.
- Lists 1-3: +25% on industrial goods, chemicals, metals, furniture, auto parts
- List 4a: +7.5% on consumer goods: apparel, footwear, electronics, toys
Section 232: Steel and aluminum
25% additional duty on steel and aluminum products from most countries. Some countries have negotiated exemptions or quota arrangements. The provisions cover HTS chapters 72-73 (steel) and 76 (aluminum), plus derivative products.
How to calculate total duty
- Classify the product: get the 10-digit HTS code
- Look up the MFN rate: the base rate in the HTS schedule
- Check Chapter 99 provisions: Section 301/232/reciprocal tariffs
- Check FTA eligibility: does the origin country have an FTA?
- Check AD/CVD orders: product and country-specific anti-dumping duties
- Add it all up: MFN + all additional duties = total
The real number most importers miss
Most trade compliance tools (including the USITC's own website) show you the MFN rate. That's Layer 1. They don't show Layers 2-5 because those come from different legal authorities (USTR, Commerce, presidential proclamations), published in different Federal Register notices, codified in different parts of the tariff schedule (Chapter 99 provisions like 9903.88.03).
The result: importers can badly underestimate their duty liability. A compliance officer budgeting "Free" duty on steel fasteners from China (7318.15.20) would have missed the 77.1% importers paid in July 2026. A team budgeting face masks from China at the 7% MFN rate would have missed the 21.9% paid.
The Chapter 99 data is public: it's in the same USITC schedule that defines the MFN rates. But the link from a code to its additional duties is stored in footnotes that most tools strip out. The Census figures in our API come at it from the other side: what was actually collected under Chapter 99 on past imports.
Supply chain implications
The stacking of tariffs is reshaping global supply chains:
- China+1 strategy: companies diversifying manufacturing to Vietnam, India, Mexico to avoid Section 301
- Nearshoring to Mexico: USMCA eliminates duties entirely for qualifying goods, vs 24-50%+ from China
- First-sale valuation: using the manufacturer's price (not the middleman's) as the dutiable value to reduce the base on which percentages are calculated
- Foreign Trade Zones: deferring or reducing duties through FTZ operations
Understanding exactly how duties stack is the first step in optimizing your import costs. The classification determines which rates apply: get it wrong and you either overpay or face penalties.