U.S. Customs Duty Calculator: How to Estimate Import Costs by HTS Code

A medical device distributor in Ohio got a $340,000 CBP supplemental duty bill fourteen months after their goods cleared customs. The original entry was filed correctly. What changed: a post-entry audit reclassified seven product lines to higher-rate HTS codes, retroactively applying Section 301 China tariffs the company had not budgeted for. Their estimated import cost was off by 23%.

That kind of gap is common. Most importers run the math using only the HTSUS column 1 rate, the nominal duty printed in the tariff schedule, and stop there. The actual charge stack on a U.S. customs entry can include three or four additional layers on top of that number, none of which appear on the same page. A U.S. customs duty calculator that does not account for all of them produces a figure CBP will not recognize.

The HTSUS rate is only one of four or five charges on every entry

The U.S. customs duty rate on any shipment is not a single number. It is a stack. The Harmonized Tariff Schedule of the United States (HTSUS) publishes roughly 17,000 ten-digit classification codes, each carrying a column 1 general rate. That rate is the floor, and for many product categories from China, it's also the smallest number on the bill.

Section 301 tariffs add 25% on most Chinese-origin goods across thousands of HTS codes. Certain electronics and solar products land at 7.5%. Section 232 tariffs impose 25% on steel articles and 10% on aluminum regardless of origin. Antidumping and countervailing duty orders layer rates from 2% to over 400% on specific products from named countries, each assessed separately from everything else.

A shipment of steel fasteners from China can carry the column 1 general rate, Section 232, Section 301, and an applicable AD order simultaneously. Those charges are calculated on the same customs value and billed as separate line items on the CBP Form 7501 entry summary. The HTSUS page for that HTS code shows only the column 1 rate. The rest live in separate CBP databases that the importer, broker, or tariff calculator must query independently.

We've talked to import managers who discovered the gap only when CBP issued a CF-28 notice. By then, the entry had already liquidated.

How to calculate U.S. import duty: the five variables CBP actually uses

Accurate duty estimation requires five inputs. Get any one wrong and the number is wrong, sometimes by enough to flip a sourcing decision.

HTS code. The 10-digit HTSUS classification is where everything starts. Classification errors at the 8-digit level frequently shift the applicable rate by 10 or more percentage points. CBP's Centers of Excellence and Expertise routinely issue CF-28 requests for information and CF-29 notices of action when an importer's code does not match CBP's read of the product. An HTS code lookup that returns the correct 10-digit code is the prerequisite for everything else. Without it, the rest of the calculation is built on sand.

Country of origin. Not country of export. The substantial transformation test, established in Torrington Co. v. United States (1989), determines where goods were actually made. Goods assembled in Vietnam from Chinese components often retain Chinese origin under that test, triggering Section 301 even when the shipment departs from Ho Chi Minh City. Origin determines the applicable column rate, FTA eligibility, and exposure to every additional duty layer.

Customs value. Defined under 19 CFR Part 152 as transaction value: invoice price plus assists, royalties, and proceeds payable to the seller, minus international freight and insurance if separately itemized. CBP audits this directly. Underreported value on formal entries above $2,500 can trigger penalty assessments under 19 USC 1592, on top of whatever duty was underpaid.

Entry type. The Section 321 de minimis threshold of $800 carried zero duty for most origins until May 2025. That changed. Chinese-origin and Hong Kong-origin goods above $0 now face standard duty rates under Federal Register Vol. 90, No. 84. Formal entries above $2,500 require a CBP Form 7501. Importers who built e-commerce or small-parcel operations around de minimis as a cost reduction mechanism are now recalculating from scratch.

AD/CVD exposure. These rates are not in the HTSUS. A separate check against the CBP AD/CVD database and the USITC case list is required. Cash deposit rates apply at time of entry. Final assessed rates come after CBP administrative review, which can produce additional bills two or three years later. That is exactly what hit the Ohio distributor.

Section 301, Section 232, and AD/CVD: additional duties most calculators miss

As of 2025, the USTR maintains Section 301 Lists 1 through 4A covering approximately $370 billion in annual import value. List 3 goods carry a 25% rate. List 4A goods carry 7.5%. Section 301 has been in place since 2018 and was reaffirmed through USTR review in 2025. Importers still modeling around it as temporary are building the wrong cost structure. We see this regularly in companies that shifted production to Southeast Asia expecting tariff relief that did not materialize because the origin analysis was never done.

Section 232 steel and aluminum tariffs, issued under Presidential Proclamations 9704 and 9705, apply across HTS chapters 72, 73, and 76 regardless of whether goods originate in China, Europe, or Canada. Derivative articles, meaning finished products made from steel or aluminum rather than the raw materials themselves, were pulled into Section 232 coverage through subsequent proclamations. A import duty calculator that skips derivatives understates liability on finished manufactured goods. Most free tools miss this entirely.

AD/CVD orders are where the numbers become genuinely unpredictable. The Commerce Department's AD order on cold-rolled steel flat products from China carries a cash deposit rate of 265.79% for certain manufacturers. The CVD order on softwood lumber from Canada sits at 14.19% as of the 2025 administrative review. Rates are exporter-specific: two factories in the same city can carry different AD rates depending on their individual review history. The importer cannot look at the country and assume a single number applies.

For Canadian-origin goods specifically, the Canada import duty calculator methodology runs through a structurally different regime. Canada Border Services Agency maintains its own AD/CVD case list, and CUSMA/USMCA preferential rates eliminate column 1 duties on most qualifying goods. The U.S. stack calculation does not translate across the border.

Free trade agreement rates and GSP: when your HTS code carries a lower rate

When an HTS code qualifies for a preferential rate under a U.S. free trade agreement, the lower rate appears in the HTSUS Special subcolumn of column 1. The United States maintains 14 active FTAs covering 20 countries. USMCA rates appear under CA or MX designators. Korea is KR. Singapore is SG. The rate in that column is available only if the importer claims it correctly.

Claiming an FTA rate is not automatic. It requires a certificate of origin or origin statement satisfying the agreement's specific requirements. For USMCA, the Rules of Origin in Annex 4-B govern qualification through tariff classification change rules, regional value content thresholds, and product-specific rules that vary by HTS chapter. An electronics importer sourcing from Mexico needs to verify that non-originating inputs satisfy the applicable RVC threshold. Getting this wrong means paying column 1 rates on goods that should have qualified for zero duty, with no recovery after liquidation.

The Generalized System of Preferences has been lapsed since early 2025. Congress has not renewed it. Importers still running landed cost models with GSP rates from India, Brazil, or Indonesia are using numbers that no longer apply. Column 1 general rates are the operative floor until further notice.

For goods entering from the UK, the UK import duty calculator applies UKGT rates under a tariff schedule that diverged from the EU's combined nomenclature after Brexit. U.S. importers of UK-origin goods apply HTSUS column 1 rates with no FTA reduction. No bilateral agreement is in effect between the two countries as of 2025.

Why your landed cost estimate still comes out wrong

Even when all five duty variables are correct, the landed cost is still wrong if it stops at duty.

Merchandise Processing Fee applies to formal entries at 0.3464% of customs value, with a minimum of $31.67 and a maximum of $614.35 per entry under the 2025 CBP fee schedule. Harbor Maintenance Fee applies to ocean shipments at 0.125% of cargo value. Broker fees, inland drayage, warehousing, and insurance stack on top. None of these appear in a customs duty calculation, and on a high-volume import program, MPF alone adds up fast.

First-sale valuation is the mechanism importers most often leave on the table. It allows declaring customs value based on the manufacturer's price to the middleman rather than the middleman's price to the U.S. importer, reducing the dutiable base on multi-tier supply chains. CBP accepts first-sale claims where the importer can document that the first sale was destined for U.S. export and priced at arm's length. That documentation requirement is where most claims fall apart: without contemporaneous records establishing export intent at time of sale, CBP rejects the claim. The reduction, when it holds, applies simultaneously to all ad valorem charges.

We've watched companies run clean compliance programs for years and still carry six-figure duty exposure because their broker was using the wrong HTS code and nobody revalidated it. The code was not obviously wrong. It was plausible. But the correct 10-digit classification sat in a different chapter with a 7.5% rate differential and active Section 301 coverage. Three years of entries. Nobody checked. The protest window on most of those entries had long since closed.

The CBP protest process under 19 USC 1514 allows post-entry correction within 180 days of liquidation. After that the entry is final. Lenzo tracks HTS rate changes and classification updates so importers can identify entries where the applicable rate has shifted since first filing, before the protest window closes.

FAQ

My freight forwarder gave me a duty estimate — why did the actual CBP bill come out higher?

Freight forwarder estimates almost always use only the HTSUS column 1 general rate. They do not routinely check for Section 301 tariffs on Chinese-origin goods, Section 232 exposure on steel or aluminum content, or active antidumping and countervailing duty orders on your specific product and exporter. Any of those can add 10% to 265% on top of the base rate, calculated on the same customs value. If your goods have Chinese origin or any steel content, treat the forwarder's number as a floor until you verify against the CBP AD/CVD database and the current USTR Section 301 list.

What is the U.S. customs duty rate on goods from China?

For most Chinese-origin goods, the effective rate is the column 1 HTSUS general rate plus a 25% Section 301 tariff. List 4A goods carry 7.5% Section 301 instead. Steel and aluminum products add a further 25% or 10% Section 232 on top of both. Products may also carry antidumping and countervailing duty rates that vary by manufacturer, updated annually through CBP administrative reviews. The combined effective rate on many Chinese-origin manufactured goods exceeds 30%. In categories with active AD orders, total duty regularly exceeds 50% of customs value.

Is there a free U.S. customs duty calculator that covers Section 301 and AD/CVD?

CBP does not publish an official calculator. The USITC DataWeb provides HTS code lookup with general duty rates. The CBP AD/CVD search database covers antidumping and countervailing duty orders separately. No single free tool currently queries all three sources simultaneously and returns a complete stacked rate for a given HTS code, country of origin, and exporter. Most free calculators return only the column 1 rate, which understates actual duty liability for any Chinese-origin or steel-content product.

How does country of origin affect my import duty if the goods shipped from a third country?

Country of origin is determined by substantial transformation, not by the country on the shipping documents. Goods assembled in Vietnam, Malaysia, or Mexico from Chinese components often retain Chinese origin for tariff purposes under the Torrington standard. Section 301 tariffs apply regardless of where the shipment physically departed. CBP has increased audit focus on this since 2025. Misrepresenting origin on a formal entry can trigger penalties under 19 USC 1592, separate from the duty underpayment.

What happens if I used the wrong HTS code and my entry already liquidated?

After liquidation, the duty rate is final. The CBP protest process under 19 USC 1514 allows a challenge within 180 days of the liquidation notice. Once that window closes, the classification cannot be corrected in either direction. If the error overstated duty, the 180-day clock is the only path to a refund. If the error understated duty, CBP can still assess additional charges under prior disclosure procedures, but the importer loses the right to contest the classification. Liquidation dates are in ACE. Pulling that report against your current HTS codes quarterly is a cheap way to stay inside the window.

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The prior disclosure process under 19 CFR Part 162 is the correct response to a discovered classification error, not silence. An importer who self-discloses a duty underpayment before CBP initiates a formal inquiry faces a penalty of 20% of the unpaid duty rather than the standard civil penalty rate, which can reach four times the unpaid duty amount under 19 USC 1592. The math on disclosure is straightforward. Most companies delay because no one wants to write the check. The ones who wait for CBP to find it write a much larger one.