How US import duty is calculated (with a worked example)
Import duty isn't one number — it's a stack. This walks through the exact calculation from customs value to the final bill, with a real worked example including base duty, Section 301, MPF and HMF.
April 30, 2026 · 7 min read
Ask five importers how duty is calculated and you'll get five half-answers, because the honest answer is "it depends on four or five things that each have their own rules." But the structure is completely learnable. Once you see the calculation laid out in order, you can compute the duty on anything — and spot when a quote you've been given is wrong.
Step 1 — establish the customs value
Duty is charged on the customs (entered) value, which is normally the transaction value: the price actually paid or payable for the goods when sold for export to the United States. Certain additions apply (assists, packing, royalties in some cases). Whether freight and insurance are included depends on your Incoterms — but for the ad valorem duty itself, the value is generally the FOB/ex-works price of the goods.
Step 2 — classify and read the base rate
Classify the product to its 10-digit HTS line and read the Column 1 general rate. This is the most-favored-nation rate that applies to normal-trade-relations countries. If it's an ad valorem rate you multiply it by the customs value; if it's specific ($/unit) you multiply by the quantity; if it's compound you do both.
Don't have the HTS line yet? Find it in seconds.
Find my HS codeStep 3 — add the additional tariffs by origin
This is the step estimates most often miss. Depending on the country of origin, additional duties may stack on top of the base rate: Section 301 for Chinese-origin goods, Section 232 for steel and aluminum, plus newer reciprocal measures. These are almost always ad valorem and they add to — rather than compound with — the base rate.
Step 4 — add the customs fees
- Merchandise Processing Fee (MPF): 0.3464% of the customs value, with a per-entry minimum and maximum CBP adjusts annually.
- Harbor Maintenance Fee (HMF): 0.125% of the value, on cargo arriving by ocean at a US port.
A full worked example
Import 500 pairs of leather shoes from China. Customs value $20,000. The base HTS rate for many leather-upper shoes is around 8.5% (confirm your exact subheading), and a Section 301 duty applies to the Chinese origin. Ocean freight, so HMF applies.
- Customs value: $20,000.
- Base duty at 8.5%: 0.085 × $20,000 = $1,700.
- Section 301 (say List 4A, 7.5%): 0.075 × $20,000 = $1,500.
- MPF at 0.3464%: 0.003464 × $20,000 = $692.80 (within the annual min/max — verify the current cap).
- HMF at 0.125%: 0.00125 × $20,000 = $25.00.
- Total duty and fees: $1,700 + $1,500 + $692.80 + $25.00 = $3,917.80.
That's roughly a 19.6% effective duty-and-fee load on a line whose "headline" base rate was 8.5%. The Section 301 layer more than doubled the duty. This is why origin matters as much as classification.
Start freeWhat the calculation does NOT include
Duty and fees are only part of landed cost. Freight, insurance, customs brokerage, bonds and inland transport are real costs too — they just aren't part of the duty calculation itself. Keep them separate in your head: duty is a percentage of customs value; logistics is what it costs to move the box.
Run your own numbers with every layer itemised and sourced.
Calculate import dutyA note on accuracy
Every rate in the worked example is illustrative and tied to a real HTS line, but your exact subheading, origin and the live Chapter 99 measures decide your actual bill. Always confirm against the current schedule — and remember nothing here is a customs ruling, only an informational estimate.
Base rates used here come from the US schedule of record — confirm your specific line before filing.
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