How to Calculate Import Duty and Tariffs (With Examples)

Calculating import duty looks simple on paper, since each rate is applied to the customs value and the results are added together. For customs brokers and importers, the harder part is making sure the figure on the entry is the right one. 

In 2026, a single line can carry a base rate, more than one Section 301 duty, a Section 232 duty, and fees on top. Each of these depends on three inputs: the HTS code, the country of origin, and the customs value. Those inputs come from the commercial invoice, the certificate of origin, and the other shipment documents. 

When one of them is wrong, the duty is wrong, even if every step of the math is correct. This guide works through the calculation step by step, with examples. It then covers the document errors behind wrong duty figures and how to catch them before filing.

What determines your import duty

Every duty calculator works from the same three inputs, and each input comes from a document in your shipment file. So the first step in how to calculate tariffs is to confirm these three inputs:

• HTS classification: The Harmonized Tariff Schedule gives each product a 10-digit code, and that code sets the duty rate. A wrong HTS code therefore leads to a wrong rate.

• Country of origin: CBP treats the country where the goods were made, produced, or grown as the origin. Another country becomes the origin only if the goods were substantially transformed there. The country the goods ship from does not decide the origin.

• Customs value: US law values most imports at the price actually paid or payable for the goods. Certain buyer costs, like packing, selling commissions, assists, and royalties, are added to that price.

An import tariff calculator applies the rates correctly only when these inputs are correct. The final duty figure is only as accurate as the shipment documents behind it.

Types of duties and tariffs that apply

A US import line can carry several duties at once, and each duty is reported on its own line of the entry summary.

1. Base HTSUS rate

The base rate is the general rate listed next to the 10-digit HTS code. A qualifying free trade agreement claim can bring this rate down to zero.

2. Section 301 duties on Chinese goods

This layer applies to Chinese-origin goods on USTR's covered lists. However, USTR has extended 178 product exclusions through November 9, 2026, so goods that match an exclusion skip this layer until then.

3. Section 232 duties

Since April 6, 2026, Section 232 has added 10% to 50% on the full customs value of steel, aluminum, and copper articles and their derivatives. This duty applies regardless of the country of origin.

4. Country-based duties

Since July 24, 2026, a separate Section 301 action has added 10% or 12.5% to goods from 60 economies. Goods from China pay 12.5%, while import tax from India includes a 10% layer. For Japan, this duty only tops up the base rate to 12.5%, so import duty from Japan on a line already at that rate gets nothing added. USMCA duty-free goods and metals like steel, aluminum, and copper are exempt from this layer. Separately, certain Canadian goods carry a 50% duty under Section 338.

5. Antidumping and countervailing duties

Commerce sets AD/CVD rates by product and country, and often by producer and exporter. CBP collects these duties as a cash deposit at entry, which means the producer and exporter named on your documents decide the rate.

6. Excise tax

Imported alcohol and tobacco carry federal excise tax, which TTB administers and CBP collects at entry.

Each layer is calculated separately on customs value and then added together. This is why a china tariff calculator that shows only the base rate will understate what most Chinese-origin lines owe.

How to calculate import duty & tariffs

The duty on any US import line follows the same five steps, and each step depends on a figure taken from the shipment documents. To show how to calculate tariffs from China and other origins, the steps below follow one example line: a nylon backpack from China with a customs value of $10,000, arriving by ocean.

Step 1: Find your HTS code

The HTS code has 10 digits. The first six follow the international Harmonized System, and the last four are specific to the US. You reach the code by moving from the chapter to the heading and then down to the 10-digit line, and that path depends on the product description on the commercial invoice.

For example, CBP places a backpack with a polyester outer surface under 4202.92.3120, which carries a 17.6% base rate. A cotton backpack falls under 4202.92.1500 at 6.3%. An invoice that only says "backpack" leaves out the material, so the line cannot be classified until someone confirms it with the shipper.

Step 2: Determine the customs value

US customs value is the transaction value, which is the price actually paid or payable for the goods. US law excludes international freight and insurance from this price, which means the CIF value that some guides use as the base overstates US customs value. The Incoterm on the invoice tells you what to adjust:

• CIF or DDP price: The price includes freight, so you deduct the actual freight and insurance costs. CBP expects proof of these costs, like a freight bill.

• EXW price: The price can leave out costs the buyer pays to other parties, like packing, selling commissions, assists, and royalties. These costs must be added back, since payments to third parties do not appear on the seller's invoice.

In our example, the $10,000 is the backpack price after these adjustments.

Step 3: Apply the base rate

The base rate can take one of three forms. An ad valorem rate is a percentage of customs value, a specific rate is a fixed amount per unit, like per kilogram, and a compound rate combines both. The backpack line carries a 17.6% ad valorem rate, so its base duty comes to $1,760. For specific and compound rates, the quantity and unit of measure matter as much as the value, which is why the packing list needs to match the invoice.

Step 4: Stack the applicable tariff layers

Each additional layer is calculated on customs value, and it is never applied to the base duty or to a running total. The backpack falls under Section 301 List 3 for Chinese goods at 25%, and it also takes the 12.5% country-based duty for China. So the line owes three separate amounts:

• Base rate: 17.6% of $10,000 = $1,760

• Section 301 (China): 25% of $10,000 = $2,500

• Section 301 (forced labor): 12.5% of $10,000 = $1,250

Together, these bring the total duty to $5,510, or 55.1% of customs value.

A steel line works differently, since steel articles under Section 232 can pay 50% of full customs value but are exempt from the country-based duty. On $10,000 of steel at that rate, the Section 232 layer alone adds $5,000. CBP also requires the country where the steel was melted and poured on each line, so the broker needs this detail from the steel supplier before filing.

Step 5: Add MPF and HMF

MPF and HMF are fees rather than duties, and they apply on top of the duty total:

• MPF: 0.3464% of customs value on formal entries. For entries from October 1, 2026, the minimum is $34.58 and the maximum is $670.86. It applies even to goods with a free base rate, unless an exemption applies.

• HMF: 0.125% of value, and it applies only to cargo unloaded from a vessel at a US port.

The backpack line adds $34.64 in MPF and $12.50 in HMF, which brings the total to $5,557.14. This is why a US import tax calculator that stops at duty will understate what you owe.

USMCA origin can remove most of these charges. Take the same $10,000 backpack, made in Mexico and shipped by truck. Without a USMCA claim, it owes $1,760 in base duty, $1,000 under the 10% country-based duty, and $34.64 in MPF, for a total of $2,794.64. With a valid USMCA claim, the line pays no base duty and is exempt from MPF, so the total drops to zero. This saving holds only if the importer has documents that prove the goods qualify under USMCA.

Common sources of error in duty calculation

Each input in the duty calculation comes from a field in the shipment documents. This means an error in any of those fields carries into the final figure, even when the arithmetic is correct. A customs calculator can only work with the inputs it receives, so these are the document errors that most often change the result: 

1. Incomplete product descriptions

The HTS code depends on details like material, construction, and use, and the entry writer reads these details off the commercial invoice. As Step 1 showed, a backpack's outer material alone moves its base rate between 6.3% and 17.6%. When the invoice leaves out the material, the entry writer has two options. 

They can hold the entry and ask the shipper, or they can pick a code that may carry the wrong rate. Section 301 lists are also tied to HTS codes, so a wrong code can change which additional layers apply to the line.

2. Inconsistent country of origin across documents

The country of origin decides which country-based layers apply. It can appear in several places, like the commercial invoice, the certificate of origin, and the port fields on the bill of lading. These fields do not always agree, since goods can be loaded at a port in a different country from where they were made.

During our demo calls, one broker explained where this goes wrong: "Is the city or the port named in the Port of Origin matching with the Country of Origin? That's where errors usually slip through." The broker's example was a port field naming Antwerp while the origin field named a country. As the broker put it, "You cannot directly match Antwerp to a country of origin like Belgium."

The mismatch matters because the rate changes with origin. For example, import tax from China includes the 12.5% country-based duty plus any Section 301 list duty. EU-origin goods, however, are topped up to a combined rate of 10%.

3. Customs value missing dutiable additions

The commercial invoice shows what the buyer paid the seller. However, US customs value also includes certain costs the buyer pays elsewhere, like packing, selling commissions, assists, and royalties tied to the sale. An assist is an item the buyer supplies to the manufacturer free or at a reduced cost, like molds or tooling used to make the goods. 

These costs do not appear on the seller's invoice, so they have to be collected from the buyer's own records. When they are left out, every ad valorem layer is calculated on a value that is too low. The understatement then repeats across the base rate, the Section 301 and 232 layers, and MPF.

4. Manual data entry on high-volume invoices

Every line on an entry needs its HTS code, value, quantity, and origin keyed into the filing software, and this step happens on every shipment. 

During our demo calls, one broker described the process: "All customs brokers receive shipment paperwork and then have to validate that information that it's correct. And once they determine it's correct, yes, it needs to be inputted into the customs software."

Since each field feeds a different part of the calculation, a single keying error changes the duty on that line. This could be a transposed digit in a value or a quantity entered in the wrong unit. The risk grows with volume, because an invoice with hundreds of lines means hundreds of fields to key and check. This is the step where reducing manual data entry has the most direct effect on accuracy.

How document automation prevents duty calculation errors

The errors in the previous section start before the entry reaches the filing software, so they have to be caught at that earlier point. Docxster is a document automation platform that sits between the documents a broker receives and the filing software they already use. The steps below follow the order of the errors above.

1. Extracting inputs from documents as received

Docxster picks up documents where they already arrive, like a shared inbox, EDI software, or a direct upload through Docxster Forms or Chat. It reads commercial invoices and packing lists whether they are printed, scanned, or PDFs, and it does not need a template for each supplier's layout. 

The fields the entry needs, like description, quantity, value, and origin, are extracted into a table. Fields with low extraction confidence go to a reviewer before they move forward. The entry writer then reviews data that is already populated, which removes the keying step where many line-level errors enter.

2. HS classification from product details

Docxster suggests an HTSUS code for each line item from the description on the supplier's invoice, with a confidence score and supporting precedents. The reviewer then confirms or changes the code. If the broker has an existing parts library, Docxster checks it first, so known items are filled in from the library and only new items go to the AI classifier.

Once the code is set, Docxster applies the base rate and the additional layers, then adds MPF and HMF. It uses the mode of transport and date of loading, so HMF applies only to ocean shipments. Docxster does not write out a full GRI argument with cited rulings for each code, so complex or disputed classifications still need the broker's own reasoning.

3. Reconciling value and origin across invoice, packing list, and BOL

Docxster compares fields across documents, including consignee, weight, pieces, and value, across the invoice, packing list, bill of lading, and certificates. It surfaces only the fields that disagree. These checks run as validation rules, and a reviewer is pulled in only when a rule fails, with the field that caused the failure highlighted on the page. Brokers can also write their own rules, so a check like whether the port on the bill of lading fits the stated country of origin can run on every entry.

4. Collection of missing information from shippers

When a required field is missing, like a product's material or a cost needed to complete customs value, Docxster requests it from the shipper. The request goes through Docxster Forms or Chat, with email as a fallback. Docxster then reads the reply and writes the answer back to the entry. This replaces the manual follow-up that holds an entry when an invoice description is too thin to classify.

5. Transfer of entry-ready data to the filing system

Docxster does not replace the brokerage system or the filing platform. Once the data is extracted, classified, and validated, Docxster pushes it into the filing software the broker already uses. For custom or proprietary platforms, it connects through an API and webhooks. The entry writer reviews and approves a figure that has already been checked against the documents behind it, instead of building that figure field by field.

Accurate duty figures and the documents behind them

The math behind a duty figure stays the same on every entry. However, the figure is only as accurate as the HTS code, origin, and customs value that go into it, since each of these comes from the shipment documents.

This is why the errors covered in this guide change the duty even when every rate is applied correctly. Examples include a description too thin to classify, or an origin that differs across documents.

Docxster reads your shipment documents as they arrive and suggests the HTS code for each line. It also checks the invoice, packing list, and bill of lading against each other before the data reaches your filing software. If you want to see how this works on your own shipment files, you can book a demo with Docxster.