HS codes and tariff classification: how to find your duty rate

What an HS code actually is

Every duty rate you'll ever pay traces back to one thing: how your product is classified. The Harmonized System (HS) is the international product-classification language that customs authorities in more than 200 countries use to decide what your goods are — and therefore what rate applies. Get the code right and your numbers are defensible. Get it wrong and you're either overpaying on every shipment or building up a liability that surfaces, with interest, in an audit years later.

The HS is administered by the World Customs Organization and is structured as a hierarchy of digit pairs. The first six digits are the same everywhere:

Chapter (first 2 digits) — the broad category. Chapter 61 is knitted apparel; Chapter 85 is electrical machinery.
Heading (4 digits) — the product group within the chapter. 6109 is T-shirts and singlets.
Subheading (6 digits) — the internationally standardized product. 6109.10 is cotton T-shirts.

Those six digits are your common ground. A 6109.10 cotton T-shirt is a 6109.10 cotton T-shirt whether it lands in Sydney, Los Angeles, or Rotterdam.

National extensions: where the rate actually lives

The 6-digit code tells customs what the product is. The duty rate lives in the national extension that each country bolts on. Countries add their own digits to draw finer distinctions and attach tariff rates and statistical codes.

In the United States, the schedule is the Harmonized Tariff Schedule (HTS), and a full code is 10 digits — the 6-digit international subheading plus a US tariff line (digits 7–8) and a statistical suffix (digits 9–10). Australia uses the Working Tariff under the same WCO framework, with its own 8-digit tariff lines and statistical codes. The EU has its 10-digit TARIC; the UK its own 10-digit tariff. So your code is portable up to six digits — past that, you must read the destination country's own schedule.

This matters because the duty rate, and any preferential rate under a free-trade agreement, hangs off the full national code, not the 6-digit stem.

How the code drives your rate — and the special tariffs

Once you have the national code, the base duty rate is whatever the tariff schedule lists against that line. But for some destinations the base rate is only the starting point.

For US imports especially, additional tariffs stack on top of the base HTS duty and are keyed to the HTS code and the country of origin:

Section 301 duties on China-origin goods
Section 232 duties on steel and aluminum
IEEPA tariffs

These are added on top of the base rate and assessed on the same customs value — they don't replace it, they pile onto it. Because they depend on both the code and the origin, two identical-looking products from different countries can carry very different total duty. Rates here change frequently, so treat any figure you find as "verify today" and confirm against the official US sources rather than a number you saw months ago. (For the mechanics of stacking, see the guide on US Section 301, 232 and IEEPA tariffs.)

The code also drives the base you apply the rate to. The US and Australia assess duty on the FOB/transaction value (international freight and insurance excluded), while most other countries use CIF — but the rate itself always comes from the classification. (See CIF vs FOB and duty vs VAT vs tariff.)

Looking up a code on the official schedule

Self-classification is the importer's job — customs doesn't assign your code for you. Use the official, free tariff tools rather than a forwarder's guess:

United States — the USITC HTS search and CBP guidance. Search the HTS, then read the chapter and section notes before you settle on a line.
Australia — the Australian Border Force Working Tariff (the Combined Australian Customs Tariff Nomenclature and Statistical Classification, "the Tariff").
Internationally — start from the WCO 6-digit subheading, then jump into the destination country's national schedule.

A reliable working method:

Identify the chapter from the product's essential nature (what it is, not what it's for).
Narrow to a heading, then a subheading, reading the legal notes at the top of each section and chapter — those notes override your intuition.
Apply the General Rules of Interpretation (GRI) when a product could fit more than one heading. GRI 3, for example, classifies composite goods by the component that gives them their essential character.
Drop into the national extension to read off the rate and any FTA preference.

Common classification pitfalls

These are the traps that catch importers most often:

Classifying by use or marketing, not composition. A "fitness tracker" isn't a sports good; it's an electronic device. The tariff cares what it is.
Material and construction blindness. Apparel codes split on knit vs woven and on fiber content. A cotton/polyester blend can fall under a different line — and rate — than pure cotton, decided by which fiber predominates by weight.
Sets and kits. A boxed set isn't automatically one code. GRI 3 may classify the whole set by its essential-character component, or you may have to break it out.
Parts vs complete articles. A "part" often has its own heading, and "parts of general use" (screws, springs) are frequently excluded from the obvious chapter by a legal note.
Ignoring section and chapter notes. These are legally binding and routinely exclude things you'd expect to be included. Skipping them is the single most common source of a wrong code.
Trusting the supplier's code. Your overseas seller classifies for their export schedule, not your import schedule. Their 6 digits may be fine; their national digits are irrelevant to you, and sometimes their 6 digits are wrong too. You are the importer of record — the liability is yours.

When you need certainty: binding rulings

If a product is high-volume, borderline between two headings, or commercially sensitive on rate, don't live with ambiguity — request a binding classification ruling from the customs authority before you import. In the US these are CBP rulings (issued through the eRulings system and searchable in the CROSS database); Australia issues Tariff Advices. A binding ruling gives you a written, legally relied-upon classification for that product, which protects you in an audit and lets you quote landed cost with confidence. Searching existing published rulings for similar goods is also one of the fastest ways to sanity-check a code you've arrived at yourself.

Putting it to work

Once you have the right national code and rate, feed it into the rest of the landed-cost math — duty base, import VAT/GST, and fees. You can run the full calculation in the Australia import duty calculator or the US import duty calculator, and walk through the whole stack in how to calculate landed cost.

Classification isn't a one-time chore. Schedules get re-numbered (the HS is revised roughly every five years), product designs change, and special tariffs move. Record the code you used and the date you verified it, and re-check before each new product launch or sourcing change. The code is the foundation everything else stands on — it's worth getting right.