Customs duties for small importers: how the number is actually calculated

Short answer: your import duty is calculated as the duty rate for your product's HS classification applied to the customs value of the shipment — and the customs value is not always the product price on the invoice. Under some shipping terms it includes freight. On top of duty, US formal entries carry Merchandise Processing Fees and, for ocean shipments, a Harbor Maintenance Fee. The rates themselves change — often, in the current tariff environment — so this article teaches the mechanism and tells you where to verify the current numbers, rather than printing a table that's stale next month.

That framing is deliberate. Duty rates are set by government action and revised on short notice; as of October 2026 the tariff landscape has been volatile enough that any specific percentage quoted in a blog post is a liability. What doesn't change is the arithmetic. Learn the five inputs and you can price any rate change into your landed cost in minutes.

Input 1: the HS code

Every product is classified under the Harmonized System — a standardized code (six digits internationally, extended to ten in the US) that determines the duty rate. A dog harness, a leather handbag, and a nylon backpack sit in different headings with different rates. Classification is where most small-importer errors live:

• Wrong code = wrong rate, either direction. Over-classification costs you money on every entry. Under-classification risks back-duty assessments if customs reclassifies later — and look-back exposure is a real thing.
• Your supplier's code suggestion is a suggestion, not a ruling. Factories classify for their export paperwork; the import-side classification is the importer's responsibility.
• How to check: the US Harmonized Tariff Schedule is searchable at hts.usitc.gov (US International Trade Commission — verified live, October 2026). Search by product keyword, read the heading notes, and when two candidates are plausible, a customs broker or a binding ruling from CBP settles it cheaply relative to the alternative.

Input 2: the customs value

Duty is calculated on the customs value — generally the transaction value (price actually paid), but which costs sit inside it depends on your shipping term and valuation method. Two practical consequences:

• Under FOB and similar terms, freight is typically added to the customs value for US entry purposes along the lines of the CIF-style build-up (cost, insurance, freight to the US boundary, per CBP's valuation rules — confirm the exact build-up with your broker for your term). Under an EXW quote you'd be adding origin haulage too.
• Under-invoicing is not a strategy. Suppliers sometimes offer to declare a lower value to "save duty." The declared value anchors your entire compliance position — valuation disputes, insurance claims, and any customs examination all run off it. As the importer of record, the liability is yours, not the factory's.

Input 3: the duty rate (and why we won't print one)

The rate comes from the tariff schedule for your HS code — a base rate that can be modified by trade actions, origin-country measures, and exclusions that appear and expire on their own schedule. This is the layer that has moved repeatedly in recent years, which is why mechanism-over-numbers is the only durable advice:

• Look up the base rate for your HS code at the USITC's HTS site.
• Ask your broker (or check CBP and Federal Register notices) whether any additional measures currently apply to your product and origin country — as of October 2026, layered tariff actions are the norm, not the exception.
• Re-verify at every price renegotiation and at least quarterly. A rate that moved 10 points on your bestseller's category changes your reorder math (how much inventory to order) and possibly your retail price. Rate changes also interact with timing — a delayed shipment can land under different rules than the one you priced, which is why supplier lead-time tracking belongs in the same planning loop.

Input 4 and 5: the US fees almost nobody budgets

Beyond duty, formal US entries carry user fees — these are published by CBP and adjusted periodically, so verify current figures on CBP's User Fee Table (verified live, October 2026), but the structure is stable:

• Merchandise Processing Fee (MPF): an ad-valorem fee on formal entries with a minimum and maximum per entry — as of October 2026, CBP's table shows $34.58 minimum / 0.3464% / $670.86 maximum per formal entry, figures that get adjusted, so check before relying on them. Note the structure: the per-entry minimum matters enormously for small shipments. A $900 order and a $90,000 order both pay at least the minimum, which is why tiny ocean LCL shipments carry surprisingly high percentage overheads.
• Harbor Maintenance Fee (HMF): 0.125% of merchandise value on ocean imports per CBP's current table. Air shipments don't pay HMF — one of the small offsets when comparing air against ocean on small orders.
• Informal entry fees apply to low-value shipments below the formal-entry threshold ($2.77–$12.45 per the October 2026 table, depending on entry type).
• Broker and clearance fees are commercial charges from your broker/forwarder, on top of the government fees — itemized separately. One planning note: these fees are per entry, so on very small orders the fixed overhead can outweigh the freight-mode saving you'd get from cheaper transit — do the per-entry math before choosing the cheapest-looking route.

Worked example (illustrative numbers, mechanism-only): 1,000 bottles of hot sauce at $0.50/unit FOB, ocean freight $300, classified under an HS code carrying, hypothetically, a 6% base rate with no additional measures. Customs value ≈ $800 (goods + freight, per your broker's build-up for the term). Duty ≈ 6% × $800 = $48. MPF ≈ 0.3464% × $800 = $2.77 — under the minimum, so $34.58 applies. HMF ≈ 0.125% × $800 = $1. Total government charges ≈ $84 ($48 duty + $34.58 MPF + $1 HMF) — the minimums are the story, not the rates — and broker fees are a separate commercial charge from your broker or forwarder, not a government one, itemized on top. Run your own numbers with the current rates each time; that's the whole point of mechanism over table.

De minimis: the rule that stopped being a loophole

US de minimis (Section 321) allowed low-value shipments to enter duty-free — the basis of the direct-from-China parcel model. That era is over: CBP suspended the de minimis exemption for mail shipments, per CBP's e-commerce guidance (verified October 2026), and low-value shipment rules continue to evolve — including new informal-entry procedures for international mail whose implementation CBP extended to January 20, 2027. The practical read for a small importer:

• Don't build replenishment strategies on duty-free parcels; that structure is being closed deliberately.
• Samples and tiny validation orders now generally enter with duty and fees like anything else — budget for it.
• Watch CBP's e-commerce page for the current state of low-value rules; they are actively changing.

Why the invoice value matters more than you think

The declared value isn't just a duty input — it flows into insurance claims, freight claims, and any dispute resolution. A shipment declared at half its real value that arrives damaged gets compensated at the declared value. Declared value accuracy is the rare compliance rule that protects you when followed and exposes only you when ignored.

Common questions

How is import duty calculated on a shipment? Duty equals the tariff rate for your product's HS classification multiplied by the customs value of the shipment — the transaction value plus, under some terms and valuation methods, freight and insurance costs built up per CBP's rules. On top of duty, US formal entries add the Merchandise Processing Fee (with a per-entry minimum and maximum) and, for ocean freight, the Harbor Maintenance Fee. Verify current rates each order — they change.

What is the HS code and how do I find mine? The Harmonized System code classifies your product for customs and determines the duty rate. Search the US tariff schedule at hts.usitc.gov by product keyword, read the heading notes, and if two classifications seem plausible, ask a customs broker or request a binding ruling from CBP. Your supplier's suggested code is a starting point, not an answer — import-side classification is the importer's responsibility.

Do I pay import duty on small orders? Increasingly yes. The US de minimis exemption that let low-value parcels enter duty-free was suspended for mail shipments per CBP's e-commerce guidance (verified October 2026), and low-value entry rules are still evolving — CBP extended new mail entry procedures to January 20, 2027. Treat small shipments as dutiable in your planning and check CBP's e-commerce page for the current state of the rules.

What fees besides duty will I pay on an import? For US formal entries: the Merchandise Processing Fee (0.3464% ad valorem as of October 2026, subject to per-entry minimum and maximum per CBP's table), the 0.125% Harbor Maintenance Fee on ocean shipments, and your broker's entry fee. Because the MPF minimum applies per entry regardless of shipment size, very small shipments carry disproportionately high percentage overhead — factor that into small-batch orders.

Why do duty rates keep changing? Duty rates are set by legislation and trade actions — base tariff schedule rates modified by country-specific measures, exclusions, and suspensions that appear and expire on political timelines. Recent years have layered additional tariff actions on many origin countries. The mechanism (HS rate × customs value plus fees) is stable; the rates are not, so verify current numbers per order rather than trusting any published table.

Next step

Take your most-reordered imported SKU and build its duty line properly: HS code looked up on the USITC site, customs value built per your shipping term with your broker, MPF and HMF added per CBP's current table. That per-unit duty figure belongs in the cost basis behind every reorder decision, alongside the carrying cost of the inventory it turns into.