If you've ever looked at a customs entry and wondered why there are two HTS codes listed for a single product, Chapter 99 is the reason. It's the part of the Harmonized Tariff Schedule that most importers find confusing — and it's also the one that has the biggest impact on what you actually pay at the border.
What Is Chapter 99?
Chapter 99 is a special section of the HTS reserved for temporary modifications to the tariff schedule. Unlike Chapters 1 through 97, which classify products by what they are, Chapter 99 codes modify the duty rates of products that are already classified elsewhere. Think of it as an overlay: your product gets its base classification from its regular HTS code, and then Chapter 99 either adds additional duties or provides temporary duty reductions on top of that base.
Chapter 99 is divided into subchapters, each corresponding to a different legal authority or trade action. The most consequential ones for importers in 2026 are Subchapter III (covering Section 301 tariffs on China, Section 232 tariffs on steel and aluminum, and IEEPA-based tariffs) and Subchapter II (covering temporary duty suspensions and reductions enacted by Congress).
How Chapter 99 Codes Work in Practice
Here's something that wasn't obvious to me when I first started working with trade data: Chapter 99 codes don't replace your product's regular HTS classification — they run in parallel. When you file a customs entry, you declare both the regular HTS code (which determines the base duty) and the applicable Chapter 99 code (which adds or subtracts from that base).
For example, a steel product might be classified under HTS 7208.51 (regular duty: Free) but also subject to Chapter 99 code 9903.80.01 (Section 232 tariff: 25%). The result is a total duty of 25%. Some products are hit by multiple Chapter 99 provisions — a Chinese steel product could be subject to both Section 232 and Section 301 tariffs simultaneously.
The Major Chapter 99 Subchapters You Need to Know
Section 301 (Subchapter III, 9903.88.xx)
These are the China tariffs. They cover four lists of products (Lists 1–4) at rates of 7.5% to 25%, with some strategic sectors like EVs and semiconductors at even higher rates following the 2024 review. The codes in the 9903.88 range each correspond to a specific list and rate.
Section 232 (Subchapter III, 9903.80.xx)
These cover steel and aluminum tariffs at 25% and 10% respectively. Originally targeted at most countries, various exclusion agreements later narrowed the scope. Derivative steel and aluminum products were added over time, expanding the reach beyond raw metals.
IEEPA Tariffs (Subchapter III, 9903.01.xx)
The International Emergency Economic Powers Act (IEEPA) tariffs are among the newest Chapter 99 additions. Imposed via executive authority, these codes have been created, paused, modified, and sometimes removed at a pace that makes them particularly challenging to track. If you're trying to build a comprehensive list of IEEPA-related Chapter 99 codes for refund analysis or compliance purposes, expect to spend real time reconciling the current codes against your entry data.
Temporary Duty Suspensions (Subchapter II, 9902.xx.xx)
Not all Chapter 99 provisions increase duties. Subchapter II contains temporary duty reductions and suspensions passed by Congress through the Miscellaneous Tariff Bill (MTB) process. These provisions reduce or eliminate duties on specific products — often raw materials or components that aren't produced domestically — for a limited period. If your product qualifies, it can mean significant savings, but the provisions are narrow and expire on set dates.
Why Chapter 99 Changes So Frequently
One of the most frustrating aspects of Chapter 99 is its instability. Codes are created and removed through Presidential proclamations, executive orders, and Congressional action. In 2025 alone, dozens of Chapter 99 codes were created, modified, or removed as trade policy shifted. This makes it essential to verify your Chapter 99 obligations against the current HTS revision before every shipment — a code that applied last month may have been revoked, and a new one may have been created.
This volatility also creates a record-keeping challenge. If you're analyzing past entries for duty refund potential — which many importers are doing right now with IEEPA tariffs — you need to reconstruct which Chapter 99 codes were active on the date of each entry, not just which codes are active today. The USITC publishes revision histories that can help, but it's painstaking work.
Practical Tips for Managing Chapter 99
After working with this data extensively, here's what I'd recommend. First, don't rely on memory or spreadsheets from six months ago — always check the current HTS revision for your Chapter 99 obligations. Second, when analyzing historical entries, use the USITC revision archive to determine which codes were active on each entry date. Third, if you're building internal tools or reports around Chapter 99 data, design them to handle frequent code changes gracefully. And finally, if you're considering filing for refunds on IEEPA or other Chapter 99 tariffs, work with a customs broker or trade attorney who can navigate the specific refund process and documentation requirements.