Methodology
How the numbers are sourced — and what they are not
PortRobin is only useful if it's honest about what it doesn't know. This page explains exactly where every duty figure comes from, and why nothing here is a customs ruling.
The honesty contract
Every duty figure in the dataset follows one rule, with no exceptions:
- A rate is set only when we verified it from an authoritative source — the USITC HTS, CBP, USTR or the Federal Register — and it always carries that source URL and the date we last checked it.
- The AI classifier picks the code; the rate always comes from the dataset, never the model. An LLM never invents a duty rate.
- A blank value renders as “verify on the HTS”, never a guess. Where a heading’s rate genuinely varies across subheadings, we say so rather than pick one.
- A rate of 0 is a real, sourced finding (“Free” — duty-free), distinct from “we haven’t verified this line.” The engine only ever computes on sourced rates.
Where each figure comes from
USITC Harmonized Tariff Schedule
The master US classification and the general (Column 1) and Column 2 duty rates. Our source of record for every base rate.
cbp.govU.S. Customs and Border Protection (CBP)
The statutory user fees (MPF, HMF), the $800 de-minimis rule and its 2025 changes, and CSMS bulletins on how measures are applied at entry.
ustr.govOffice of the U.S. Trade Representative (USTR)
The Section 301 China tariff lists and their rates, published as annexes by 8-digit HTS code.
bis.doc.govCommerce / BIS & the Federal Register
Section 232 steel and aluminum actions and the 2025–26 IEEPA reciprocal tariffs, with their effective dates.
How measures stack
A finished duty figure is a stack. The base general (Column 1) rate applies to most origins. On top of it, additional programmes can apply: Section 301 (China), Section 232 (steel & aluminum), and the 2025–26 IEEPA reciprocal actions. Our landed-cost engine adds each verifiedmeasure and computes the CBP Merchandise Processing Fee and Harbor Maintenance Fee to their statutory formulas. A measure we can’t verify is shown and flagged, but never folded silently into the total.
We currently track 103 seeded HTS lines across 96 chapters, 8 additional measures and 36 trade partners — and the dataset grows as we verify more lines.
These are the most fast-moving numbers in all of trade. The verifiedOn date next to a figure is load-bearing: confirm the live rate for a real entry.
This is an estimate, not a customs ruling
Everything PortRobin returns — classifications, duty rates and landed-cost totals — is an informational estimate for planning. It is not legal, customs or compliance advice, and it is not a binding classification.
The binding classification of a good is CBP’s. For a decision you can rely on, consult a licensed customs broker or request a binding CBP ruling. Tariffs, lists and de-minimis rules change frequently and some 2025–26 measures are subject to active litigation — always confirm the current figure against the official HTS and CBP before you rely on it for a real entry.
Something look wrong?
If you think a rate is out of date or a source has changed, email hello@portrobin.comwith a link to the current source and we’ll re-verify it.
See the methodology in practice
Every code page shows this same sourced, stacked breakdown — with the date each figure was verified.