Your 10-digit HTS code tells you the base duty on a product. What it doesn't tell you — not on that line, anyway — is whether the product also owes Section 301, Section 232, or another add-on tariff. Those are the duties that turn a 16.5% rate into a 24% one, and they're filed separately, in a different chapter of the schedule. Here's where to look so they don't ambush you on the invoice.

Step 1 · Read the Duty Columns and Spot the Footnote

Pull up your code on the US International Trade Commission (USITC) HTS at https://hts.usitc.gov. Every line shows a "Rates of Duty" block split into three columns — and knowing what each one is comes first:

Where Section 301 hides in the HTS lookup USITC HTS Search · hts.usitc.gov Results for “6109.10” HEADING / SUBHEADING ARTICLE DESCRIPTION RATES OF DUTY 1 · General 1 · Special Column 2 6109.10.0012 cotton · men’s T-shirts, knitted, of cotton: Men’s or boys’: Other T-shirts 16.5% * Free 90% ★ That asterisk is the footnote — and the whole point. Hover it in the HTS and it points you into Chapter 99: 9903.88.15 · Section 301 (China): +7.5% That 7.5% stacks on top of the 16.5% base rate. Your customs entry has to list both lines — the 6109.10.0012 classification and the 9903.88.15 add-on.
The three duty columns, and the footnote that leads to the real add-on tariff in Chapter 99. (Illustration; rates shown are representative.)
  • Column 1 – General. The standard rate, formally the Normal Trade Relations (NTR) rate — you'll also see it called Most Favored Nation (MFN). This is what most of the world pays. For our cotton T-shirt, it's 16.5%.
  • Column 1 – Special. The reduced or duty-free rate available under a free trade agreement (FTA) or preference program — USMCA and others — if your goods qualify and you claim it. It usually reads "Free," followed by letter symbols telling you which programs apply.
  • Column 2. The punitive rate — a leftover from the 1930 Smoot-Hawley tariff — that applies only to countries without Normal Trade Relations. As of 2026 that's a short list: Cuba, North Korea, Russia, and Belarus. For most importers it's irrelevant; just know it isn't "embargo," it's "no NTR," and the rates are brutal (90% on that same T-shirt).

Here's the catch: none of those three columns include Section 301 or Section 232. Read only the duty columns and you'll think a Chinese cotton T-shirt owes 16.5%. It doesn't — and the schedule tells you so, if you catch the footnote.

Step 2 · Search the Footnote Code for the Real Rate

The footnote names a Chapter 99 code, but not the duty — for that, you run a second search. Copy the code from the footnote (here, 9903.88.15), clear the search box, and look it up on its own. This time you land in Chapter 99, the schedule's section for the temporary, stacked-on tariffs, and the line spells out the add-on:

Searching the footnote code reveals the add-on rate USITC HTS Search · hts.usitc.gov 🔍  9903.88.15 ← a new search HEADING ARTICLE DESCRIPTION RATE OF DUTY 9903.88.15 Products of China — U.S. note 20(t) to subch. III Section 301, List 4A · effective Sep 1, 2019 + 7.5% over the base rate ★  You’ve found the add-on. The rate is written as an increment — “+ 7.5%” on top of the 16.5% base: 16.5% + 7.5% = 24% total Then open the referenced U.S. note (here, note 20) for the exact scope of the list and any product exclusions that might cover your code.
Step 2: search the footnote code itself. The Chapter 99 line spells out the add-on duty. (Illustration; rates representative.)

Read it carefully, because Chapter 99 lines work differently from your base code. The rate isn't a standalone number — it's an increment: "the duty provided in the applicable subheading + 7.5%." You add it to your base rate, so 16.5% + 7.5% is a real duty of 24%. Which code you land on depends on the list — Lists 1 through 3 add 25%, List 4A adds 7.5%, and some sector-specific codes go much higher. The description also points to a U.S. note (here, note 20 to subchapter III); open it, because that's where the exact product scope and any exclusions live. And on the actual customs entry, both lines are declared — your 6109.10.0012 classification and the 9903.88.15 add-on — and you pay both.

Where to Check Each Add-On Tariff

  • Section 301 (China). Follow the HTS footnote to the 9903.88 provision, then cross-check the US Trade Representative's official lists and exclusions at https://ustr.gov. Rates run from 7.5% (List 4A) to 25% (Lists 1–3) and higher on targeted sectors.
  • Section 232 (steel & aluminum, plus "derivative" products). These have their own Chapter 99 headings (the 9903.80 and 9903.85 series). If you import metal or metal-content goods, check whether your code is caught by a 232 provision.
  • Other current actions. Tariff policy moves fast, and new duties keep arriving as fresh Chapter 99 provisions. When in doubt, read the current Chapter 99 notes in the USITC tool and check US Customs and Border Protection (CBP) messages (CSMS) at https://www.cbp.gov for the latest.
  • Antidumping & countervailing duties (AD/CVD). These work differently — they're tied not to your HTS line by list, but to specific products from specific producers under a Commerce Department order. Your HTS code is a screening signal, not the final word. See our AD/CVD guide.

Origin Is the Trigger — Not Where You Bought It

Whether Section 301 applies turns on the product's country of origin — where it was made or "substantially transformed" — not the country you bought it from or shipped it out of. A product routed through a third country is still subject to China 301 duties if China is its origin. Get the origin right first; see understanding country of origin.

Confirm It, Because It Changes

Discuss and verify this with your customs broker. HTS navigation is genuinely complicated — the columns, the footnotes, Chapter 99, the U.S. notes and the exclusions — and under “reasonable care” the responsibility for getting it right sits with you, the importer, not your supplier or your forwarder. Use this article to know what to look for; then confirm the exact classification and the add-on tariffs with a licensed customs broker before you file.

Lists get revised, exclusions expire, and new tariffs appear on short notice — all the more reason to confirm current provisions rather than assume last year's still hold. Check for any active exclusion that covers your code, and build the add-ons into your landed cost — not your regrets. For the full duty math, see how to research the tariff on your product; to read the base code itself, see how to read a 10-digit HTS code.

The Bottom Line

The duty columns show the base rate; the footnote shows the truth. When you look up a code, read all three columns, then hunt for the asterisk and follow it into Chapter 99 — that's where Section 301 and the other add-on tariffs hide. Miss it and you've under-budgeted every unit; catch it and you know your real duty before you write the order.

This is general guidance, not legal or customs advice. Tariff lists, rates, and exclusions change frequently, and classification can be complex — confirm current provisions with a licensed customs broker or CBP before you rely on them.

When you price a new product, do you check for Section 301 and other add-on tariffs up front — in the HTS, with your broker, or a duty calculator — or do they tend to surface later on the invoice? We'd like to hear where the surprises have come from.