How to Estimate Import Duties (With Worked Examples)

A supplier quote of $8,000 FOB Shanghai is not an $8,000 shipment. By the time duties, tariffs, and government fees are added, that shipment can land at $9,500, $11,000, or more, and the difference between those outcomes is almost entirely knowable before you order. Estimating import duty is simple arithmetic once you know which numbers to use: your product's customs value, its duty rates, and a handful of fees that apply regardless of what you import.

The short version: take the price you paid your supplier, multiply it by each duty rate that applies to your product, add the merchandise processing and harbor maintenance fees, and you have your customs bill. The rest of this guide shows exactly where each number comes from, with three worked examples so you can copy the method directly. A sourcing agent can sanity-check your math against the supplier's quote before you commit, which is one of the quieter services CN Ally provides for importers planning their first orders.

The duty formula in one line

Here is the complete estimate in a single expression:

Estimated customs bill = (customs value x duty rate stack) + MPF + HMF

The "duty rate stack" is the sum of every percentage-based duty that applies to your product: the base MFN rate from your HTS code, plus any Section 301 tariffs for China-origin goods, plus any anti-dumping or countervailing duties and Section 232 tariffs that cover your category. MPF (Merchandise Processing Fee) and HMF (Harbor Maintenance Fee) are flat-structure government fees layered on top.

Each of the next three sections finds one of those inputs. Work through them in order and the examples later will make immediate sense.

Step 1: Pin down the value customs actually taxes

For US imports, duty is calculated on the transaction value: the price actually paid or payable for the goods when sold for export to the United States. In practice, for most importers this is simply the supplier's invoice price, which is usually quoted FOB (Free on Board). International freight and insurance are excluded from the dutiable value in the US. That exclusion matters more than most beginners expect, because it means a $5,000 freight bill does not inflate your duty.

This is also where a common and expensive mistake creeps in. Many online guides are written for EU or UK importers, where customs value is CIF: cost plus insurance plus freight to the border. If you apply CIF logic to a US shipment, you overstate your duty base by the full cost of international shipping. Get the rule for your destination right first: US uses the transaction value (typically FOB), the EU and UK use CIF.

Two edge cases worth knowing. If you and your supplier are related parties, CBP applies extra scrutiny to make sure the price reflects an arm's-length transaction. And if your invoice bundles product cost with freight on a single line, your broker will need the freight broken out so the dutiable value can be stated correctly. Ask for that breakdown at the quote stage, not after the goods ship.

Step 2: Find every duty rate in your stack

Your base duty rate comes from your product's 10-digit HTS code, looked up in the Harmonized Tariff Schedule of the United States at hts.usitc.gov. This is free and official. If you have not classified your product yet, that classification is the single highest-leverage step in this whole process: the wrong code can mean the wrong rate in either direction, and "the supplier told me the HS code" is not due diligence. Our guide to HS codes for imported products walks through the classification method.

For China-origin goods, the stack usually has more than one layer:

Duty layer · What it is · How you find the rate

• MFN base duty: The standard rate for your HTS code, same for all WTO members · hts.usitc.gov, the "General" column
• Section 301 tariffs: Additional China-specific duties under the Trade Act of 1974, still in effect · HTSUS Chapter 99 notes and current USTR notices; rates vary widely by product category
• Section 232 tariffs: Product-specific trade-remedy duties (steel, aluminum, autos, semiconductors, and others) · HTSUS Chapter 99 and Commerce Department guidance
• AD/CVD duties: Anti-dumping and countervailing duties on specific products from specific producers · Check whether your product is covered by an AD/CVD order before you price anything

A few honest caveats. Section 301 rates have ranged historically from 7.5% to 100% depending on the product list, and the tariff landscape changed substantially through 2025 and 2026, with some temporary measures expiring and others being litigated. Any article that hands you a single "current China tariff rate" without a date is doing you a disservice. Always confirm the live rate for your HTS code in the tariff schedule and current USTR notices, and read our tariffs and China sourcing overview for how the layers fit together.

Step 3: Add the fees everyone forgets

Duties are only part of the customs bill. CBP also collects user fees that apply whether or not your product carries any duty at all, and beginners routinely leave them out of estimates.

Merchandise Processing Fee (MPF). Charged on formal entries at 0.3464% of the entered customs value, subject to a minimum and a maximum that adjust annually for inflation. For FY2026 (October 1, 2025 through September 30, 2026), the minimum is $33.58 and the maximum is $651.50 per entry, per CBP's published user fee schedule. That means the floor binds on entries valued under roughly $9,700 (you pay $33.58 even though the percentage math says less), and the cap binds above roughly $188,000. From October 1, 2026, the FY2027 figures rise to a $34.58 minimum and $670.86 maximum. Shipments under $2,500 that clear as informal entries pay a small flat automated fee (currently $2.69) instead of the percentage calculation.

Harbor Maintenance Fee (HMF). A 0.125% fee on the cargo value that applies only to ocean shipments arriving at US ports. Air freight pays no HMF.

The practical upshot: a product with a 0% duty rate still generates an MPF charge on every formal entry, and an ocean shipment always carries HMF. "Duty-free" never means "fee-free," and on small shipments the fees can exceed the duty itself, as the third worked example shows.

Worked example 1: a $20,000 ocean shipment

The scenario: 2,000 units of a consumer product at $10 each, FOB Shanghai, shipped by ocean. All duty rates below are illustrative planning figures, not quotes for your product; the point is the method.

Line item · Calculation · Amount

• Customs value (FOB): 2,000 x $10 · $20,000.00
• Base MFN duty, 4% illustrative: $20,000 x 4% · $800.00
• Section 301 tariff, 25% illustrative: $20,000 x 25% · $5,000.00
• MPF, 0.3464% (within floor and cap): $20,000 x 0.3464% · $69.28
• HMF, 0.125% (ocean): $20,000 x 0.125% · $25.00
• **Estimated customs bill: $5,894.28**

That is roughly 29.5 cents of customs cost per dollar of product value, before freight, insurance, broker fees, and inland delivery. Per unit, customs adds about $2.95 to a $10 product. This is the math that decides whether a product is viable: fold it into your landed cost calculation and compare against your target selling price before you place the order.

Worked example 2: a $6,000 air shipment with 0% base duty

The scenario: 500 units of an electronic accessory at $12 each, FOB Shenzhen, shipped by air. The product's base MFN rate is 0%, and an illustrative 7.5% Section 301 rate applies.

Line item · Calculation · Amount

• Customs value (FOB): 500 x $12 · $6,000.00
• Base MFN duty, 0%: $0.00
• Section 301 tariff, 7.5% illustrative: $6,000 x 7.5% · $450.00
• MPF, 0.3464% = $20.78, raised to floor: minimum applies · $33.58
• HMF (air freight): not applicable · $0.00
• **Estimated customs bill: $483.58**

Two lessons here. First, 0% base duty does not mean a $0 customs bill; the tariff layer and the MPF floor still apply. Second, notice how the MPF floor works: the percentage math produced $20.78, but CBP charges the $33.58 minimum. On air shipments there is no HMF to offset that, so small air shipments carry a proportionally heavier fee load.

Worked example 3: a $1,800 shipment and the MPF floor

The scenario: a small test order of 300 units at $6 each, FOB, shipped by ocean. Illustrative base duty of 3.2%, no additional tariff layers.

Line item · Calculation · Amount

• Customs value (FOB): 300 x $6 · $1,800.00
• Base MFN duty, 3.2% illustrative: $1,800 x 3.2% · $57.60
• MPF, 0.3464% = $6.24, raised to floor: minimum applies · $33.58
• HMF, 0.125% (ocean): $1,800 x 0.125% · $2.25
• **Estimated customs bill: $93.43**

The duty itself is $57.60, but the fees add $35.83, which is more than 60% of the duty amount. This is the pattern that surprises first-time importers: on small shipments, fixed-structure fees dominate. If you are budgeting a sample-size order, estimate the fees explicitly rather than assuming they scale down with the shipment.

Six mistakes that wreck duty estimates

1. Using CIF value for a US shipment. If your forwarder quotes door-to-door pricing, do not feed the all-in number into the duty formula. Strip out international freight and insurance first. Duties on a $20,000 product with $4,000 of freight should be calculated on $20,000, not $24,000.

2. Forgetting MPF and HMF entirely. Most online "duty calculators" in blog posts stop at the duty rate. The worked examples above show how much of the bill those two fees represent, especially on smaller shipments.

3. Using a stale Section 301 rate. Rates and exclusions change; product-specific exclusions have expired and been reinstated in cycles. A rate quoted in a 2024 article is not a plan. Check the current HTSUS Chapter 99 notes for your code, and see our Section 301 tariffs guide for how to track changes.

4. Trusting the supplier's HS code. Suppliers sometimes suggest codes with lower duty rates, whether from optimism or habit. Their code describes the goods for Chinese export purposes; your US import classification is your legal responsibility. Verify it independently.

5. Treating a forwarder's estimate as the final bill. Freight forwarders give planning estimates, and the actual duty is determined by CBP at entry. Build a 5 to 10% contingency into your margin math for classification and valuation adjustments.

6. Ignoring currency and rounding. If your supplier invoices in RMB, convert at a realistic rate and note the date; small FX moves on a large order change the dutiable value. CBP also rounds and applies its own appraisement rules, so treat your number as an estimate with a range, not a promise.

Tools that do the math for you

You do not have to do this by hand every time. A few tools are worth knowing, with honest notes on each:

• hts.usitc.gov is the official USITC tariff search. Free, authoritative, and the only place to confirm your base duty rate and check Chapter 99 for additional tariffs. It is not beginner-friendly, but it is the source of truth.
• Commercial duty calculators (several free ones cover China-to-USA lanes) can speed up the arithmetic and some track current tariff layers. Treat them as planning tools: verify which tariff layers they include and when they were last updated, because an outdated layer list produces a confidently wrong number.
• Your customs broker's quote remains the tiebreaker. Brokers classify products daily and see how CBP actually treats edge cases. If your own estimate and the broker's differ by more than a few percent, find out why before the goods ship.

One more note on de minimis, since older articles still mention it: the $800 duty-free threshold was suspended for goods from China and Hong Kong in May 2025, then for all countries in August 2025. Do not build any estimate around a duty-free allowance that no longer exists for commercial imports.

Frequently asked questions

Do I pay import duty on the shipping cost?

For US imports, no. Duty is assessed on the transaction value of the goods, which excludes international transportation and insurance. Freight still counts toward your total landed cost, just not toward the dutiable value. (The EU and UK work differently: their customs value includes freight and insurance to the border.)

What if my product's duty rate is 0%?

You still owe the MPF on a formal entry and HMF on ocean shipments, and any applicable Section 301, Section 232, or AD/CVD layers still apply on top of the 0% base rate. A 0% base rate is a good start, not a finished estimate.

Can I get a refund if I overpay duties?

Yes, through mechanisms like duty drawback and protests of CBP decisions, but both are procedural and time-limited. The better strategy is an accurate estimate up front, which is what this article is for. Talk to a licensed customs broker or drawback specialist about your specific situation.

Does a DDP quote from my supplier include all of this?

DDP (Delivered Duty Paid) means the seller is contractually responsible for duties and import clearance, so a proper DDP quote should cover the customs bill. The catch is in the word "proper": confirm in writing exactly which charges the quote includes, especially for courier-handled DDP on small parcels, where the courier's own brokerage and advancement fees sometimes sit outside the seller's quote.

How accurate are online import duty calculators?

As accurate as their inputs. They compute correctly from whatever HS code, value, and tariff layers you enter, so the error is almost always in the inputs: a wrong classification, a stale tariff layer, or a CIF value fed into a US formula. Use them for planning, and have a broker validate anything you will sign a purchase order against.

When to estimate it yourself, and when to hand it to a broker

Do the estimate yourself when you are comparing products, screening suppliers, or deciding whether a category is worth pursuing at all. The method in this article takes ten minutes and is accurate enough for go/no-go decisions. Hand it to a licensed customs broker when real money is committed: before you sign a purchase order, before you choose between two close HS classifications, and any time AD/CVD orders might touch your product.

The decision rule is simple. If the estimate says the product works with room to spare, proceed and let the broker confirm. If the estimate says it barely works, the product does not work; fees, freight, and FX will eat the sliver that is left. Margin math done honestly at the planning stage is the cheapest quality control in importing, and it costs nothing but ten minutes and a calculator. If you want a second pair of eyes on the numbers before you commit, email hi@cnally.com and we will check your duty estimate against the supplier quote as part of the sourcing review.