Customs Basics
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How Tariffs Actually Work: HS Codes, MFN Rates and Trade Agreements

The same product can face wildly different duty depending on one code, one origin country, and one trade agreement.

Classification System
Harmonized System (HS) codes
Default Rate
MFN (Most Favoured Nation)
Can Be Lowered By
A qualifying trade agreement

Three Things Decide Your Duty Rate

Import duty isn't one number per product — it's the outcome of three separate questions, each of which can change the answer. First, what is the product, precisely, under the Harmonized System (HS) — an internationally standardised classification code used by customs authorities worldwide. Second, what is that destination country's standard (MFN) duty rate for that specific code. Third, does the product's country of origin qualify for a lower rate under a trade agreement between the origin and destination countries.

Get any one of the three wrong — an imprecise HS code, an assumption about the standard rate, or an unproven origin claim — and the duty calculation can be significantly off, in either direction.

1. HS Codes: More Specific Than People Expect

The Harmonized System, maintained internationally and implemented by each country's own tariff schedule (like the US HTSUS or the EU's Combined Nomenclature), classifies goods into thousands of specific categories. 'Clothing' isn't one code — cotton shirts, synthetic jackets and wool coats can sit in different chapters with meaningfully different duty rates. The more precisely you classify a product, the more accurate the duty estimate — a vague or generic code is one of the most common sources of a wrong customs outcome.

2. MFN Rate: The Default, Before Any Agreement

Most Favoured Nation (MFN) is the standard duty rate a country applies to imports from any other WTO member, absent a specific trade agreement or exemption. It's the baseline you'd pay without any special treatment. One real, notable MFN example: under the WTO's Information Technology Agreement, most electronics and computing products — laptops, phones, semiconductors — enter at 0% MFN duty in participating countries including the US and EU, because that specific product category was carved out to 0% by international agreement.

How a Trade Agreement Can Change the Outcome

ScenarioLikely rate applied
No trade agreement between origin and destinationStandard MFN rate for that HS code
Origin qualifies under a preferential trade agreement (e.g. EU-UK TCA)Reduced or 0% rate, if proof of origin is provided (e.g. a Supplier's Declaration or EUR.1)
Goods pass through a third country without sufficient transformation thereOrigin agreement generally doesn't apply — origin is where the last substantial transformation occurred, not where it was shipped from

One Category Worth Knowing About: Tariff-Rate Quotas

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Some products — notably dairy, sugar and certain agricultural goods — are subject to tariff-rate quotas (TRQs): a lower rate up to a certain import volume, then a much higher rate above it, sometimes well over 100%.

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This means a general duty 'range' for a broad category like 'food and beverages' can understate the real exposure for a TRQ-protected product specifically — it's worth checking whether your exact product falls into one of these categories before assuming a general range applies.

Frequently Asked Questions

What is an HS code and why does it matter?

It's an internationally standardised product classification code used by customs authorities to determine duty rates, restrictions and statistics. The exact code your item falls under — not a general category — determines the specific duty rate that applies.

What does MFN mean?

Most Favoured Nation — the standard duty rate a country applies by default to imports from other WTO members, before any trade agreement or exemption is applied.

How do I know if a trade agreement lowers my duty rate?

Check whether a trade agreement exists between the product's country of origin and the destination country, and whether the product meets that agreement's specific rules of origin — usually requiring documented proof like a Supplier's Declaration or a certificate of origin.

Why do some products have such high duty rates?

Certain categories — including some agricultural products under tariff-rate quotas — are deliberately protected with higher rates above a certain import volume. This isn't arbitrary; it reflects specific trade policy for that product category, not a general rule that applies everywhere.

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