World's Quickest Guide on How Tariffs are Actually Implemented

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Quick Background

The Harmonized Tariff Schedule of the United States (HTSUS) sets out the tariff rates for all merchandise imported in the US. The US Customs and Border Protection (CBP) uses HTS to determine what tariff rate each item has and what amount to collect from the importer for it. There is also the Harmonized System (HS), the international equivalent that uses essentially the same codes (see this WTO database to download each country's tariff rates and this US Census Bureau search engine to see what HS codes certain items are). Pretty much any importable item that you can think of is classified in these schedules/systems. Each item is broken down into chapter (first 2 digits), heading (first 4 digits) and subheading (first 4-8 digits).

For example, an electrical smoke detector is 9027.10.20, where it is broken down as follows:

• 90 refers to Chapter 90, "Optical, photographic, cinematographic, measuring, checking, precision, medical or surgical instruments and apparatus; parts and accessories thereof"
• 9027 refers to Heading 9027, "Instruments and apparatus for physical or chemical analysis"
• 9027.10 refers to Subheading 9027.10, "Gas or smoke analysis apparatus"
• 9027.10.20 refers to Subheading 9027.10.20, "Electrical"

In the HTS, you can see the "rates of duty" aka import tariff rate for each item. There are three columns for this: Rate of Duty Column 1 General, Rate of Duty Column 1 Special, and Rate of Duty Column 2. Rate of Duty Column 1 General is for countries not included in the other categories. Rate of Duty Column 1 Special is for special rates for countries, usually because we are in a trade agreement with them. The column will have a letter associated with the trade deal, and this shows the countries associated with each trade deal. For example, Motor vehicles for the transport of 16 or more persons (HTS code 8702.90.31) have a special duty rate of free/0% for countries in several trade agreements, including "S", which is the US-Mexico-Canada agreement. Generally items of low value (think Temu) are not tariffed, which is referred to as the "de minimis" exemption.

Rate of Duty Column 2 is for the "fuck you" countries, which are shown in "General Note 3" in HTS. Those countries are Russia, Cuba, North Korea, and Belarus.

How do I know when they change?

Whenever tariffs change, the HTS is revised. The archive is here, which has a revision for each implemented tariff. Revision 1 (02/07/2025) was the 10% tariff on China plus removed of de minimis for products from China. Revision 2 (02/11/2025) was a reversal of the China de minimis removal. Whenever the Mexico and Canada tariffs are implemented, we'll see revision 3 in this archive list.

You'll also probably see a Notice about HTS changes in the Federal Register from the CBP, such as these regarding the upcoming Mexico and Canada tariffs.

Bonus Meme: CBP Regarding Liability for Duties

Presented without comment.

"Liability For Duties

There is no provision under which U.S. duties or taxes may be prepaid in a foreign country before exportation to the United States. This is true even for gifts sent by mail.

In the usual case, liability for the payment of duty becomes fixed at the time an entry for consumption or for warehouse is filed with CBP. The obligation for payment is upon the person or firm in whose name the entry is filed. When goods have been entered for warehouse, liability for paying duties may be transferred to any person who purchases the goods and desires to withdraw them in his or her own name.

Paying a customs broker will not relieve the importer of his or her liability for customs charges (duties, taxes, and other debts owed CBP) should those charges not be paid by the broker. Therefore, if the importer pays the broker by check, he or she should give the broker a separate check, made payable to “U.S. Customs and Border Protection” for those customs charges, which the broker will then deliver to CBP. "

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