How to Calculate Import Duty: A Complete Guide for 2026

Calculating import duty is the most consequential financial calculation an importer makes — a single digit change in your HTS code can shift your duty rate from 0% to 25%, and missing a Section 301 surcharge can trigger retroactive penalties under 19 USC §1592 that reach back five years. This complete guide covers every component of the import duty calculation, from classification to final payment, with worked examples for every common import scenario in 2026.

The Import Duty Formula — Complete Breakdown

The total cost to import goods into the United States includes more than just the customs duty rate. Here is the complete formula:

Total Import Cost = Customs Value + Customs Duty + Section 301/232 Additional Duties + ADD/CVD + MPF + HMF + Broker Fees + Port Charges + Inland Freight

Each of these components is calculated differently and some are cumulative. This guide walks through every element.

Component 1: Customs Value (The Duty Base)

The United States uses transaction value (19 USC §1401a) as the primary method for determining the customs value — the base amount on which duty is calculated. Transaction value is the price actually paid or payable for the goods when sold for export to the United States, with specific adjustments.

What You MUST Include in Customs Value

• Selling commissions: Commissions paid by the buyer to the seller's agent. Buying commissions (paid to YOUR agent) are excluded.
• Royalties and license fees: If the buyer must pay them as a condition of the sale. Software license fees bundled with hardware imports are dutiable.
• Assists: Materials, tools, dies, molds, design work, or engineering provided by the buyer to the seller for use in producing the imported goods. This is CBP's #1 valuation audit finding — undeclared assists.
• Packing costs: Cost of containers, covering, and labor for packing — whether itemized or included in the price.

What You EXCLUDE from Customs Value

• International freight and insurance after importation (the US uses FOB-based valuation, not CIF)
• US customs duties and federal excise taxes
• Buying commissions
• Interest charges meeting 19 USC §1401a(e) criteria

Component 2: The Duty Rate — Three Columns

Each HTS subheading carries up to three rate columns:

Column 1 General (MFN)

Applies to goods from WTO member countries with Normal Trade Relations status — over 95% of US imports. Rates range from Free (0%) to over 30%. This is the default rate for most imports.

Column 1 Special (FTA / Preference Programs)

Preferential rates under Free Trade Agreements and preference programs. Often Free (0%). Available programs include USMCA (Mexico, Canada), KORUS (South Korea), US-Singapore FTA, US-Australia FTA, GSP (Generalized System of Preferences), and others. Claiming these rates requires the goods meet the FTA's rules of origin and that the importer maintains supporting documentation for 5 years.

Column 2

Applies to countries without Normal Trade Relations status (currently Cuba and North Korea). Rates are significantly higher — often 20-90%.

Reading Compound and Specific Rates

Not all rates are simple percentages. Common formats:

• Ad valorem: "5.3%" — percentage of customs value
• Specific: "0.7¢/kg" — fixed amount per unit of weight/quantity
• Compound: "0.5¢/kg + 5.5%" — both specific and ad valorem components apply

Component 3: Section 301 Additional Duties

Section 301 tariffs on Chinese imports are the most impactful additional duty layer for US importers. They apply ON TOP of the Column 1 rate and are calculated on the same customs value base:

Section 301 List	Duty Rate	Key Product Categories
List 1 (July 2018)	25%	Industrial machinery (Ch. 84), medical devices (Ch. 90)
List 2 (August 2018)	25%	Plastics (Ch. 39), chemicals (Ch. 28-38), base metals (Ch. 72-76)
List 3 (September 2018)	25%	Electronics, furniture, textiles, toys, most consumer goods
List 4A (September 2019)	7.5%	Apparel, footwear, mobile phones, certain electronics

Calculation: A product with 5% Column 1 rate and 25% Section 301 List 3 duty pays 30% total (5% + 25%), both calculated on the customs value. Section 301 is NOT compounded on the Column 1 duty — both are ad valorem on the customs value.

Component 4: Section 232 National Security Tariffs

Section 232 applies to steel and aluminum imports:

• Steel (25%): Most Chapter 72-73 products. Country exemptions: Australia, Argentina, Brazil, South Korea (quota), Canada, Mexico (USMCA).
• Aluminum (10%): Most Chapter 76 products. Same country exemptions as steel, minus quota countries.

Section 232 is cumulative with Section 301 where both apply — rare but possible for certain steel/aluminum derivative products from China.

Component 5: Anti-Dumping / Countervailing Duties (ADD/CVD)

ADD/CVD rates are product-specific and country-specific, ranging from 1% to over 500%. They are applied IN ADDITION to all other duties. The Commerce Department publishes deposit rates by exporter — your specific supplier may have a different rate than the country-wide rate.

Component 6: Merchandise Processing Fee (MPF)

MPF = 0.3464% of the customs value, minimum $31.75, maximum $614.35 (2026 rates). Applied to most formal entries (value over $2,500). MPF is a CBP processing fee, not a duty — FTAs do not reduce it.

Component 7: Harbor Maintenance Fee (HMF)

HMF = 0.125% of the value of cargo arriving by vessel. Does NOT apply to air or courier shipments.

Complete Worked Examples

Example 1: Simple MFN Import (Germany)

Import $50,000 of stainless steel kitchen utensils (HTS 8215.99) from Germany. Column 1 rate: Free. No additional duties.

Total duty: $0. Pay only MPF ($173.20) and HMF ($62.50 if ocean freight).

Example 2: Section 301 Import (China)

Import $100,000 of Bluetooth speakers (HTS 8518.22) from China. Column 1: 3.9%. Section 301 List 3: 25%.

• Column 1: $100,000 × 3.9% = $3,900
• Section 301: $100,000 × 25% = $25,000
• Total duty: $28,900

Example 3: FTA Preferential Rate (Mexico, USMCA)

Import $75,000 of automotive parts (HTS 8708.99) from Mexico. Column 1 General: 2.5%. USMCA Special: Free.

Total duty: $0 — savings of $1,875 vs. MFN. Maintain USMCA certification for 5 years.

Example 4: Triple-Layer Duty (China, Section 301 + Section 232 + ADD)

Import $200,000 of steel fasteners (HTS 7318) from China. Column 1: 3%. Section 232: 25%. Section 301 List 2: 25%. ADD on Chinese steel fasteners: 46.23%.

• Column 1: $200,000 × 3% = $6,000
• Section 232: $200,000 × 25% = $50,000
• Section 301: $200,000 × 25% = $50,000
• ADD: $200,000 × 46.23% = $92,460
• Total duty: $198,460 (99.23% effective rate)

This example shows why Chinese steel imports have dropped over 90% since 2018.

Example 5: Compound Rate + De Minimis

Import a $750 shipment of phone cases from China (HTS 3926.90). Below $800 de minimis threshold — normal duty waived. But Section 301 still applies: $750 × 25% = $187.50.

The 5 Most Expensive Calculation Mistakes

1. Using CIF value instead of FOB: The US uses FOB-based transaction value. Including international freight in your customs value means you pay duty on freight — pure waste.
2. Not claiming FTA preferential rates: If your goods qualify for USMCA/KORUS but you fail to claim at entry, CBP applies the higher General rate. Post-entry claims are possible but time-limited.
3. Ignoring Section 301: The most expensive mistake. Underpaying by even 1% across $1M in imports creates $10,000 in potential liability per entry.
4. Not declaring assists: CBP treats undeclared assists as negligence (20% penalty) or gross negligence (40%) on the duty owed on the assist value.
5. Wrong valuation for related-party transactions: If the relationship between buyer and seller influenced the price, CBP may reject the transaction value entirely.

Quick Reference: Duty Calculation Checklist

1. Classify product to the 10-digit HTS code using GRI 1-6
2. Identify the correct duty rate column (General, Special/FTA, or Column 2)
3. Determine customs value (transaction value per 19 USC §1401a)
4. Check for Section 301 applicability (Chinese-origin goods)
5. Check for Section 232 applicability (steel/aluminum)
6. Check for ADD/CVD orders (product and country-specific)
7. Calculate MPF (0.3464%) and HMF (0.125% for ocean freight)
8. Sum all components for total import cost

Disclaimer: Duty calculations are for reference only and may not reflect all applicable trade remedies. Importers are responsible for verifying their own duty rates. PoliteDraft provides reference data only — not legal or trade compliance advice.