How U.S. import duty is calculated

The sequence is fixed. First, the goods are classified to a 10-digit HTS number. That classification determines the Column 1 general rate — the base duty. Second, any preference program is evaluated: if the goods originate under a free trade agreement and the preference is claimed with a valid certification, a Special column rate may replace the general rate. Third, additional-duty programs are evaluated against the same classification and the country of origin — Section 301, Section 232, and any other active action, each under its own legal authority and its own effective dates. Fourth, federal processing fees are added: the Merchandise Processing Fee, and the Harbor Maintenance Fee if the goods arrived by vessel.

Two things are commonly misunderstood. Additional-duty programs do not always simply add together — some are structured as ceilings that cap the total rather than layers that stack on it, and some are mutually exclusive. And the duty base excludes international freight and insurance, so a shipment with expensive shipping does not owe more duty on that account.