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Tariff BasicsMay 2026 · 6 min read

How Are Tariffs Calculated?

US import tariffs aren't a single flat tax — they're a stack of rates applied to your product's customs value, determined by a 10-digit classification code. This guide walks through every component, with a worked example.

TL;DR: Tariff = (customs value × HTS duty rate) + Section 301 if from China + MPF + HMF. The calculator at the bottom does all of this instantly.

The Tariff Formula

Total Import Cost =

Customs Value

+ (Customs Value × HTS Duty Rate)

+ (Customs Value × Section 301 Rate)

+ (Customs Value × 0.3464%) MPF

+ (Cargo Value × 0.125%) HMF (ocean only)

+ Freight + Insurance

Step-by-Step: Calculating US Import Duty

1

Find your HTS code

Every import needs a 10-digit Harmonized Tariff Schedule (HTS) code. The first 6 digits are the international HS code; the last 4 are US-specific. You can look up HTS codes on the USITC website, use an AI classification tool, or ask your customs broker. The code determines your base duty rate.

Example: Women's cotton T-shirts → HTS 6109.10.00 → 16.5% base rate

2

Determine the customs value

US Customs uses the 'transaction value' — the price you actually paid for the goods. This is typically the FOB (Free On Board) price on your commercial invoice. For most calculations, customs value = invoice price.

Example: Invoice shows $10,000 for 500 T-shirts → customs value = $10,000

3

Apply the MFN duty rate

Multiply the customs value by the MFN (Most-Favored-Nation) rate for your HTS code. MFN is the standard rate applied to imports from all WTO member countries.

Example: $10,000 × 16.5% = $1,650 base customs duty

4

Check for additional tariffs

For China-origin goods, add Section 301 surcharges (7.5%–25%). For steel and aluminium from most countries, add Section 232 tariffs (25% / 10%). For some categories, check for active anti-dumping (ADD) or countervailing duties (CVD).

Example: Same T-shirts from China → additional 7.5% §301 → total duty = $1,650 + $750 = $2,400

5

Add Merchandise Processing Fee (MPF)

US Customs charges an MPF on most formal entries: 0.3464% of customs value, with a minimum of $31.67 and a maximum of $614.35 per entry. USMCA qualifying goods from Canada/Mexico are exempt.

Example: $10,000 × 0.3464% = $34.64 MPF

6

Add Harbor Maintenance Fee (HMF) for ocean shipments

Ocean imports through US ports pay HMF of 0.125% of the cargo value. Air freight is exempt.

Example: $10,000 × 0.125% = $12.50 HMF

7

Total your import costs

Add customs duty + MPF + HMF to your product cost and freight to get the true landed cost. Don't forget currency conversion if invoiced in a foreign currency.

Total landed cost: $10,000 + $2,400 duty + $34.64 MPF + $12.50 HMF + freight + insurance

Worked Example: Women's T-shirts from China

Importing $10,000 of women's cotton T-shirts (HTS 6109.10.00) from China via ocean freight.

Customs value$10,000.00
MFN duty (16.5%)+$1,650.00
§301 China (7.5%)+$750.00
MPF (0.3464%)+$34.64
HMF (0.125%)+$12.50
Ocean freight+$800.00
Total landed cost$13,247.14

How the calculation changes by country

OriginMFN RateAdditionalDuty on $10K
🇨🇳 China16.5%+7.5% §301$2,400
🇻🇳 Vietnam16.5%—$1,650
🇧🇩 Bangladesh16.5%—$1,650
🇲🇽 Mexico0%USMCA$0
🇬🇧 UK16.5%—$1,650
🇮🇳 India16.5%—$1,650

Same product (women's cotton T-shirts, HTS 6109.10), same $10,000 value. Origin country is the biggest variable.

3 common mistakes in tariff calculations

❌ Using the wrong HS code

A wrong classification — even by one digit — can mean the wrong duty rate, missed ADD/CVD orders, or customs holds. Common example: calling a bag a 'backpack' vs a 'travel bag' (different HTS, different rates).

❌ Forgetting MPF on large shipments

The MPF caps at $614.35 per entry. High-volume importers sometimes batch shipments to hit the cap and reduce per-unit MPF costs. Failing to account for MPF underestimates landed cost by 0.3–0.5%.

❌ Not checking ADD/CVD for the specific supplier

Anti-dumping duty rates vary by company, not just country. Two Vietnamese shrimp suppliers can have very different AD rates. Always check the USITC ADCVD database using the specific manufacturer's name.

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