What is Chapter 99?

Chapter 99 of the US Harmonized Tariff Schedule (HTS) contains temporary and additional duty provisions. These are not product classifications—they are reference codes that add extra duties (or restrictions) on top of the base HTS rate.

Common uses include Section 301 (trade remedies by country), Section 232 (national security tariffs, e.g. steel and aluminum), and IEEPA (International Emergency Economic Powers Act). The exact rate or rule depends on the subheading and often on country of origin.

Why are some codes "reference-only"?

Some Chapter 99 entries say things like "See 9903.xx.xx" instead of listing a numeric rate. The actual rate or condition is defined in another Chapter 99 subheading. Our API can resolve these when possible using the resolve_chapter_99 parameter on the resolve endpoint.

How it relates to Section 301, 232, and IEEPA

Section 301, Section 232, and IEEPA measures are implemented in the HTS via Chapter 99. When you look up a base product (e.g. HTS 8541.10.00), applicable additional measures— and their Chapter 99 codes—are returned separately. You need both the base rate and the additional duty (by origin) to compute total duty.

How to compute duty with the API

Use GET /api/v1/tariffs/resolve with hts, origin, and optional as_of. The response includes base tariffs and applicable additional measures. Optionally set resolve_chapter_99=true to resolve reference-only measures to numeric rates when available.