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
Example 1: Steel plate from China
The base rate is "Free" but the actual landed cost includes 50% in additional duties. An importer looking only at the MFN rate would underestimate their cost by 50 percentage points.
Example 2: Surgical face masks from China
Face masks were hit by multiple tariff waves — originally on List 4a at 7.5%, then escalated with additional provisions targeting PPE from China. An importer looking at the MFN rate of 7% would estimate duties at $700 on a $10,000 shipment. The actual bill: $8,950. This isn't a theoretical scenario — it's what CBP collects at the port.
Example 3: Cotton t-shirt from China
Example 4: Cotton t-shirt from Vietnam
Same product, different origin — 24% from China vs 16.5% from Vietnam. This 7.5pp difference is why supply chains are shifting.
Example 5: Cotton t-shirt from Mexico (USMCA)
With USMCA rules of origin met, the MFN rate is replaced by the preferential rate. 24% from China, 16.5% from Vietnam, 0% from Mexico.
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 routinely underestimate their duty liability by 2-10x. A compliance officer budgeting for "Free" duty on Chinese steel gets a 50% bill. A sourcing team comparing China vs Vietnam costs sees 7% vs 7%, when the real comparison is 89.5% vs 7%.
The Chapter 99 data is public — it's in the same USITC schedule that defines the MFN rates. But it's stored in footnotes that most tools strip out. We parse every footnote across all 26,118 HTS codes and resolve them to actual rates.
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 landed cost. The classification determines which rates apply — get it wrong and you either overpay or face penalties.