What Is HTS Chapter 99? Additional Duties Explained

Chapter 99 of the Harmonized Tariff Schedule holds temporary legislation and additional duties imposed on top of the normal duty rate, such as Section 301 duties on Chinese goods and Section 232 duties on steel and aluminum. On an entry summary, these appear as extra lines with 9903 numbers, reported alongside the product's regular HTS number. Several can stack on one product, which is why Chapter 99 is where a lot of overpayment hides.

How Chapter 99 lines work

Every imported product has a regular 10-digit HTS number from Chapters 1 to 97, which sets the base duty rate. When an additional duty applies, the entry line also carries a Chapter 99 number that adds the extra rate. The base number decides which Chapter 99 measures apply.

Common Chapter 99 measures

• Section 301: Additional duties on many Chinese goods, reported under 9903.88 numbers. See Section 301 explained.
• Section 232: Additional duties on steel, aluminum and other products covered by 232 actions.
• IEEPA: The 9903.01 lines struck down by the Supreme Court in February 2026 and now refunded through CAPE. See IEEPA tariff refunds.
• Exclusions: Some Chapter 99 numbers exist to claim an exclusion from an additional duty.

Where errors happen

• Wrong base number, which pulls in a Chapter 99 duty that should not apply.
• Missed exclusions that were available for the product.
• Wrong stacking, where duties that should not combine were both applied.
• Origin errors that trigger country-specific duties.

Frequently asked questions

Are Chapter 99 duties eligible for drawback? Section 301 duties are. Eligibility of others depends on the measure. See the duty drawback guide.

Where do I see my Chapter 99 lines? In your entry summary data. See how to download ACE data.

How Caspian checks Chapter 99

Caspian's audit checks every Chapter 99 line against the base number, origin and available exclusions. See our trade audit.

Works Cited:

• USITC: Harmonized Tariff Schedule of the United States
• USTR: Section 301 investigations