Methodology
How ImportCost produces an estimate, what it refuses to estimate, and why.
Where the numbers come from
Every tariff figure ImportCost displays originates in a published U.S. government document: the USITC Harmonized Tariff Schedule for base rates, Federal Register notices and rules for tariff actions, CBP Cargo Systems Messaging Service bulletins for implementation, and USTR notices for Section 301 scope. Nothing is derived from a competitor's cost guide, and nothing is generated by a language model.
The calculation sequence
Classification determines the Column 1 general rate. Preference programs are evaluated next, then additional-duty programs under their own authorities and effective dates, then stacking is resolved, then federal processing fees are added based on entry type and transport mode. Carrier charges are estimated separately and never mixed into the government total.
What we refuse to calculate
When a rate expression cannot be safely parsed — a specific, compound, or quota-dependent rate — ImportCost stores the original expression and marks the result for review instead of converting it to an approximate percentage. When a rule's scope depends on an annex we have not imported, the rule is surfaced as needing review rather than applied at a guessed rate. A partial answer with an honest gap is more useful than a complete answer that is wrong.
Stacking
Additional duties do not always sum. Some programs are exclusive, some replace the base rate, and some operate as ceilings that cap a total rather than layers that add to it. The engine records a decision for every rule it evaluates — applied, skipped, or superseded — and the reason, so a result can be audited rather than trusted.
Freshness
Every rule carries its own last-verified date; there is no site-wide freshness claim. The status indicator on the calculator reads from the data itself, so if verification lapses the site says so rather than presenting stale figures as current.
Automation
ImportCost does not currently run scheduled automated ingestion of CBP, USTR, or Federal Register publications. Data is imported and verified manually, and the site says so. When automated monitoring exists, this section will describe it specifically rather than implying it.