US Customs Import Duties & Tariff Stacking: A Professional's Guide
Importing commodities into the United States requires strict coordination of transaction values, proper Harmonized Tariff Schedule (HTS) classifications, and accounting for shifting statutory fees. This guide provides trade compliance officers and logistics managers a legal overview of the core mechanical rules governing customs fee calculations.
1. The FAST Act & Merchandise Processing Fee (MPF) Indexing
The Merchandise Processing Fee (MPF) is a user fee collected by U.S. Customs and Border Protection to recover the costs of processing formal entries. Under the Fixing America's Surface Transportation (FAST) Act, the ad valorem MPF rate is set at 0.3464% of the declared transaction value. However, the critical compliance aspect is that the minimum and maximum limitations are adjusted annually by CBP to account for inflation.
For Fiscal Year 2026 (running October 1, 2025 through September 30, 2026), the formal entry minimum limit is $33.58 and the maximum is capped at $651.50. Any formal cargo summary whose calculated MPF falls below the threshold triggers the flat minimum, while high-value shipments are strictly capped at the ceiling rate, shielding large-scale importers from excessive fees. Additionally, paper-based (manual) entries trigger an extra surcharge of $4.03 for FY 2026.
2. Harbor Maintenance Fee (HMF) Limitations
Unlike MPF, the Harbor Maintenance Fee (HMF) is governed by 19 C.F.R. § 24.24 and is fixed by statute at 0.125% of the declared cargo value. There is no statutory minimum or maximum fee. HMF is exclusively applied to maritime cargo arriving via waterborne transportation at designated ocean ports. Imports transported via international air cargo, truck, or rail are fully exempt from HMF, making shipping mode a primary driver in landed-cost trade-offs.
3. Section 301 and Section 232 Punitive Trade Remedy Stacking
Under Section 301 of the Trade Act of 1974, strategic Chinese imports face compounding, punitive ad valorem tariffs that stack directly on top of base Most-Favored-Nation (MFN) duties. Following the USTR's statutory four-year review, tariff rates on strategic products have escalated dramatically through 2025 and 2026:
- Electric Vehicles (EVs): 100% ad valorem duty.
- Semiconductors & Solar Modules: 50% ad valorem duty.
- EV Lithium-ion Batteries & Parts: 25% ad valorem duty.
- Non-EV Lithium-ion Batteries & Critical Minerals: 25% ad valorem duty (effectively rising from 7.5% or 0% on January 1, 2026).
- Forced Labor Surcharge: A new 12.5% surcharge (effective July 24, 2026) stacks on affected Chinese supply lines.
In addition, imports of steel and aluminum are subject to Section 232 national security safeguard tariffs of 25% and 10% respectively, unless originating from approved treaty-exempt trading partners. When evaluating landed cost, these trade remedies represent significant cash deposit requirements that must be budgeted for at the time of entry summary filing.
4. Recordkeeping & Statutory Compliance
Importers are legally required to maintain all supporting documentation, including commercial invoices, ocean bills of lading, packing lists, and CBP Form 7501 entry summaries for at least five years from the date of entry. CBP regularly audits transactions for valuation accuracy, correct HTS classification, and proper classification of country of origin.