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.
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
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
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
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
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
Add Merchandise Processing Fee (MPF)
US Customs charges an MPF on most formal entries: 0.3464% of customs value, with a minimum of $34.58 and a maximum of $670.86 per entry (FY2027, from 1 October 2026). Informal entries up to $2,500 pay a flat $2.77. USMCA qualifying goods from Canada/Mexico are exempt.
Example: $10,000 × 0.3464% = $34.64 MPF
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
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.
How the calculation changes by country
| Origin | MFN Rate | Additional | Duty on $10K |
|---|---|---|---|
| 🇨🇳 China | 16.5% | +7.5% §301 | $2,400 |
| 🇻🇳 Vietnam | 16.5% | — | $1,650 |
| 🇧🇩 Bangladesh | 16.5% | — | $1,650 |
| 🇲🇽 Mexico | 0% | USMCA | $0 |
| 🇬🇧 UK | 16.5% | — | $1,650 |
| 🇮🇳 India | 16.5% | — | $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 $670.86 per entry (FY2027). 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.