You discover you have been importing under the wrong code. There are two doors, and one closes in 180 days.

Key takeaways

• Two situations, two mechanisms. Underpayment is a prior disclosure question; overpayment is a protest or post summary correction question.
• the protest window at 180 days from the liquidation date, running per entry rather than per account — so entries expire individually and quietly.
• Prior disclosure is described across the trade compliance market as a standard service. Filing before CBP identifies an issue is the entire point of the mechanism.
• Where a tariff has been reversed or reduced retrospectively, unliquidated entries being re-liquidated automatically while already-liquidated entries require a formal protest.
• Neither is a do-it-yourself exercise. Both are sitting in the specialist market between routine brokerage and trade litigation.

Every classification review produces the same uncomfortable moment. You look at three years of entries and realize something was wrong.

Which direction it was wrong in determines everything that follows, and both directions have a clock.

This is not legal advice. Both mechanisms are described consistently as specialist work, and this guide exists so you know which conversation to have.

01If you underpaid

The exposure is the penalty regime in 19 U.S.C. § 1592, covered in the classification guide: negligence, gross negligence and fraud, with penalties reaching multiples of the duty lost or the merchandise’s domestic value.

Prior disclosure is the mechanism for coming forward before CBP finds it. Reporting names prior-disclosure filings among the standard services of the trade compliance market that grew around the 2026 tariff environment.

The logic of it is straightforward: the penalty regime distinguishes between an importer who disclosed an error and one who was caught. Filing changes which of those you are.

The timing point is the whole point. A disclosure has value while CBP has not yet identified the issue. Once an audit or an inquiry has started, the option narrows.

Which makes the discovery moment decisive. A seller who finds a classification error and decides to fix it going forward without addressing the past has made a choice about the past — see the customs holds guide on how algorithmic targeting uses importer history.

02If you overpaid

More common, and more often ignored, because nobody sends a letter about it.

Two routes, depending on where the entry is in its lifecycle:

Post Summary Correction — for entries not yet liquidated. Reporting on classification describes overpayment as recoverable through a post summary correction or protest within a limited window after liquidation.

Protest — for entries already liquidated. the window at 180 days from the liquidation date.

The detail that costs money: the window runs per entry, from that entry’s liquidation date. There is no account-level deadline and no notification you would notice. Reporting on retrospective tariff changes states the position plainly — check every liquidated entry individually and file before its specific deadline expires.

03The retrospective tariff case

This is where it stopped being theoretical for a lot of importers.

Where a tariff measure is reversed, reduced or struck down, two treatments:

Unliquidated entries — re-liquidated automatically where the system supports it.

Already-liquidated entries — requiring a formal protest within 180 days of liquidation.

So a refund you are owed can expire because nobody filed. Given how many measures moved across 2025 and 2026 — see the tariff stack guide — that is not a hypothetical for anyone importing at volume.

04When to look

Four triggers worth acting on:

After any classification review. If the review found a better code, it also found that the old one was wrong. That is a two-sided finding.

After a tariff measure changes retrospectively. Check whether your entries are affected and where each one sits in liquidation.

When a supplier changes something. Material, construction, origin. A change that moves the classification means the entries after it may be wrong even though the entries before it were right.

Before a sale of the business. Buyers reconcile COGS against supplier invoices, and an unresolved customs exposure is a diligence finding rather than a surprise.

05What this requires from you

Both mechanisms run on records:

Entry summaries — CBP Form 7501 for every entry. If you have never obtained one, the landed cost guide explains why you want them regardless.

Liquidation dates, per entry. This is the field that starts the protest clock.

Classification reasoning, dated. The file described in the classification guide — what code, when, why, and what was rejected.

Supplier documentation connecting the goods to the entries — the same supplier invoice discipline that six other systems require.

If you cannot produce those, the first step is not a filing. It is getting the records, which usually means asking your broker or forwarder for a complete entry history.

06What to do

Ask your broker for a full entry history, with liquidation dates. Most sellers have never seen one and it is the input to everything here.

Review classifications against the current schedule — four revisions in the first two months of 2026, per the tariff engineering guide.

Check liquidated entries for protest deadlines if any measure affecting you has changed. Per entry, 180 days, and nobody will remind you.

If you find an underpayment, take it to a customs attorney before doing anything else — including before filing anything or requesting a ruling that describes the product.

If you find an overpayment, act on the oldest entries first. They are the ones closest to expiring.

Do not fix it going forward and leave the past alone. That is a decision, and it is one made without advice.

Check the liquidation dates on your last twelve months of entries in ACE. Count how many are within 180 days. That number is how many protests you can still file — and it gets smaller every day.

Frequently asked

I have been using the wrong HTS code. What do I do?

It depends on the direction. Underpayment is a prior disclosure question and should go to a customs attorney before anything else is filed. Overpayment is recoverable through a post summary correction on unliquidated entries or a protest within 180 days of liquidation.

How long do I have to claim back overpaid duty?

the protest window at 180 days from the liquidation date, running per entry. There is no account-level deadline and no notification you would ordinarily notice.

What is a prior disclosure?

The mechanism for coming forward to CBP about an error before it identifies the issue. Reporting names prior-disclosure filings among the standard services of the trade compliance market, and the value depends on filing before an inquiry begins.

A tariff I paid was reversed. Do I get it back automatically?

It depends on entry status. unliquidated entries being re-liquidated automatically where the system supports it, while already-liquidated entries require a formal protest within 180 days of liquidation.

What records do I need?

Entry summaries with liquidation dates per entry, dated classification reasoning, and supplier documentation connecting the goods to the entries. If you do not have them, ask your broker for a complete entry history first.

Can I just fix it going forward?

You can, and it is a decision about the past rather than an avoidance of one. Given that importer history feeds algorithmic targeting and that penalties distinguish disclosed errors from discovered ones, it is worth making that decision with advice.

Sources

1. 19 U.S.C. § 1592(c)(4) (prior disclosure) and 19 CFR 162.74; 19 U.S.C. § 1514 (protests within 180 days of liquidation); 19 CFR 174, United States Code, Title 19; U.S. Customs and Border Protection accessed 2026-09-05
2. Reduce import duty US 2026 (unliquidated entries re-liquidated automatically against already-liquidated entries requiring a formal protest within 180 days of liquidation; checking every liquidated entry individually), Carra Globe Secondary accessed 2026-09-05
3. How American importers are cutting their 2026 duty bills (prior-disclosure filings among the services of the tariff mitigation market, alongside classification reviews, first sale valuation and drawback recovery), Big News Network Secondary accessed 2026-09-05
4. What is an HTS code? The 2026 importer’s guide (overpayment recoverable through a Post Summary Correction or protest within a limited window after liquidation; underpayment exposure under 19 U.S.C. § 1592 including duty, interest and civil penalties), Peacock Tariff Consulting Secondary accessed 2026-09-05
5. Complete guide to HTS classification 2026 (penalty tiers under 19 U.S.C. § 1592 for negligence, gross negligence and fraud), Camtom Secondary accessed 2026-09-05
6. Navigating US customs holds and exams: a 2026 guide (algorithmic targeting drawing on importer history), FreightAmigo Secondary accessed 2026-09-05