Harmonized Tariff Schedule (HTS) — a plain-English guide

Somewhere in a warehouse in Ohio, a customer service rep is arguing with a broker about whether a silicone phone case is "other articles of plastic" or "accessories of the goods it's designed for." That argument, and thousands like it every day, gets settled by one document: the Harmonized Tariff Schedule of the United States, usually shortened to HTS or HTSUS. It is the master list of every product the country imports and the exact duty owed on each one, and it is maintained by the US International Trade Commission (USITC) as the legal reference US Customs and Border Protection (CBP) uses to assess duty at the border.

If you import anything — one pallet a year or forty containers a week — you are reading the HTS, whether you know it or not. Your broker reads it on your behalf, your customs bond depends on it, and every duty invoice you've ever paid traces back to a line in it. This guide walks through how the schedule is actually built, how to read a rate off it, and the parts that catch first-time importers out.

What is the Harmonized Tariff Schedule, exactly?

The HTS is a nested classification system: every physical product that could conceivably cross a US border is assigned to a numbered slot, and each slot carries a duty rate. It is not a US invention from scratch. It sits on top of the Harmonized System (HS), an international product nomenclature maintained by the World Customs Organization (WCO) and used by more than 200 countries and customs territories to classify roughly 98% of world merchandise trade. The US takes that shared international base and extends it with its own extra digits — which is the part that trips people up, and which we'll unpack below.

How is the schedule organised?

The HTS runs from raw materials at the front to finished, manufactured goods at the back, in a nested hierarchy that gets more specific at every level. Live animals and vegetable products open the schedule; works of art and antiques close it. In between sit metals, machinery, textiles, chemicals, and everything else that moves in trade. The structure looks like this, from broadest to most granular:

• 22 sections group the schedule by broad category (Section XI, for example, covers textiles and textile articles).
• 99 chapters, the first two digits of any code, narrow that down further (Chapter 61 is knitted apparel; Chapter 84 is machinery).
• Headings, four digits, name a specific class of product (6109 is T-shirts and singlets, knitted or crocheted).
• Subheadings, six digits, are the international HS level shared with every other HS country (6109.10 narrows to cotton).
• The US statistical line, ten digits, is what CBP actually charges duty against (6109.10.0060, for example, covers certain men's or boys' cotton T-shirts).

Why does the HTS have ten digits instead of six?

Every WCO member country agrees on the first six digits so that trade statistics are comparable across borders — a shipment classified as 6109.10 in Vietnam should land on the same subheading in the US, Germany, or Japan. But countries are free to add their own extra digits underneath that shared root, for their own tariff and statistical purposes. The US uses four more digits: two for tariff-rate distinctions (a men's cotton tee can carry a different rate line from a women's cotton tee even inside the same subheading) and two purely for trade statistics, which the Census Bureau also uses for export reporting under Schedule B. The EU's equivalent structure is the TARIC code, which layers additional digits onto the same six-digit HS base for its own tariff and quota purposes — different numbers, same underlying logic.

How do you read a duty rate on the HTS?

Once you've found your ten-digit line, the rate column shows the duty in one of a handful of shapes, and knowing which shape you're looking at matters as much as the number itself.

• An ad valorem rate is a percentage of the customs value — 16.5% is a typical rate on some footwear lines, for instance.
• A specific rate is a flat amount per unit, such as $0.51 per kilogram, regardless of what the goods cost.
• A compound rate combines both — a percentage plus a per-unit amount, common in parts of the textile and agriculture chapters.
• "Free" means genuinely duty-free. Treat it as a real finding you can rely on, not a blank cell someone forgot to fill in.

Always check the unit of quantity too. Specific and compound rates are charged against that unit — kilograms, dozens, litres — so getting the unit wrong on your entry can throw the whole duty calculation off even when the classification itself was correct. A Seattle outdoor-gear importer once told her broker she'd triple-checked a subheading for insulated water bottles, only to find the actual duty line differed depending on whether the bottles were vacuum-insulated stainless steel or plastic — a distinction the marketing copy on her own packaging didn't even make. That's the kind of granularity the schedule works at.

Most classification disputes I see aren't about the wrong chapter — they're about stopping one digit too early. Clients bring me a six-digit code from a supplier invoice and assume that's the number CBP will charge against. It almost never is.

What is the difference between Column 1 and Column 2?

Every HTS line has two rate columns sitting next to each other, and reading the wrong one is an easy, expensive mistake. Column 1 applies to countries with normal trade relations (NTR, sometimes still called most-favored-nation status) — which covers almost every country the US trades with. It splits further into a "General" sub-column, the standard MFN rate, and a "Special" sub-column, which lists preferential rates available under free-trade agreements and other programmes, along with the letter codes that identify which agreement applies. Column 2 is a much higher rate reserved for the small handful of countries that do not currently have NTR status with the United States. Almost every importer only ever needs to read Column 1 General — but if you're sourcing from a country under sanctions or restricted trade status, Column 2 is the one that actually applies, and the gap between the two columns can be dramatic.

Where do Section 301 and Section 232 tariffs fit in?

Here's the part that catches almost everyone out at some point: the base rate you find in Chapters 1 through 97 is often not the whole story. Temporary and additional duties — Section 301 tariffs tied to China-origin goods, Section 232 measures on steel and aluminum content, reciprocal tariffs, and various safeguard actions — don't get written into the product's normal heading. They live in a separate part of the schedule, Chapter 99, and cross-reference back to your product's regular heading by origin and product description. To land on your true, all-in duty rate, you have to check two things: your normal Chapters 1–97 line, and any Chapter 99 provisions that apply given your product and country of origin. Skip the second check and your landed-cost estimate can be off by a wide margin — sometimes the difference between a viable margin and a loss on the container.

How often does the HTS change, and why does that matter?

The HTS is not a document you memorise once and file away. It moves on several different clocks at the same time, and a code that was correct last year can quietly stop being correct without anyone telling you directly.

• The WCO updates the underlying international HS roughly every five years, and the most recent major revision realigned thousands of subheadings worldwide to reflect new product categories like electric vehicles and e-waste.
• The USITC issues revisions to the US schedule throughout the year, often several times, as trade actions and legislative changes take effect.
• Chapter 99 measures are added, extended, or withdrawn by presidential proclamation and USTR action, sometimes with only weeks of notice.
• A code you used for years may be split into two more specific lines, merged with another, or renumbered entirely, usually with a transition note explaining the change.

A five-person homeware brand shipping ceramic mugs from a factory outside Foshan found this out the hard way when their long-used subheading was split into microwave-safe and non-microwave-safe lines in a routine revision — a distinction that changed which of their two product lines paid the higher rate. Nobody emailed them about it; their broker caught it on the next filing.

Is HTS the same thing as a customs code or a tariff number?

In everyday trade conversation, "HTS code," "tariff number," "HTS number," and "customs code" are usually used to mean the same thing: the ten-digit US statistical line that determines your duty rate. Strictly speaking, "HS code" refers to just the first six digits shared internationally, while "HTS" or "HTSUS" refers to the full US ten-digit schedule that extends it. Other countries have their own extensions of the same six-digit base under different names — TARIC in the EU, for instance — which is worth knowing if you're comparing rates across markets, but for a US import, HTS is the number that matters.

Where should you actually look up the HTS?

The authoritative, always-current version of the schedule is the USITC's online HTS. It's free, searchable, and legally definitive — every broker, importer, and customs attorney in the country ultimately checks back against it. Third-party tools, spreadsheets, and AI summaries (including this article) are useful for speed and plain-English explanation, but none of them outrank the primary source when money is on the line.

Nothing in this guide is legal, customs, or tax advice, and classification decisions with real money attached deserve a licensed customs broker or a CBP binding ruling, not just a plain-English article. PortRobin reads from the same schedule of record, adds a plain-English gloss and the applicable Chapter 99 measures, and never shows a rate it can't trace back to source.