Ask someone to estimate the duty on a shipment and they'll usually pull the MFN rate off the HTS schedule and stop there. For a lot of products from a lot of countries, that's actually the whole answer. For products caught by Section 301 and an active antidumping or countervailing duty order — which now covers far more than steel and solar panels — that MFN rate is just the first of several layers, and none of them replace each other. They all apply to the same customs value, independently, and add.
Your 5% Duty Rate Might Actually Be 125%
Each layer applies to the full customs value independently — they don't replace each other, they add.
5%
MFN (Column 1)
25%
Section 301
80%
Antidumping Duty
15%
Countervailing Duty
125%
Effective Duty Rate
#DutyStacking #Section301 #AntidumpingDuty #TradeCompliance
What This Looks Like on an Actual Shipment
Percentages are easy to wave off as abstract. Dollars aren't. Here's the same stack applied to a $50,000 customs value — a Chinese-origin product carrying both a Section 301 List 1 tariff and an active AD/CVD order, which is a genuinely common combination, not a worst-case edge scenario.
How a $50,000 Shipment Becomes $112,736
A worked example: a Chinese-origin product subject to Section 301 and an active AD/CVD order — every layer stacks on the last.
Customs Value
MFN (5%)
Sec. 301 (25%)
AD (80%)
CVD (15%)
MPF + HMF
True Landed Cost
#DutyStacking #Section301 #AntidumpingDuty #LandedCost
The Merchandise Processing Fee and Harbor Maintenance Fee at the end are almost rounding errors next to the antidumping and countervailing layers, but they're real, and they're often the only two costs people remember to budget for beyond the MFN rate — MPF (0.3464% of value, capped at $651.50 per entry) and HMF (0.125% of value, ocean shipments only) are genuinely small. The gap between "the duty rate we quoted the customer" and "the duty we actually owed" almost never comes from those. It comes from Section 301 and AD/CVD being left out of the estimate entirely.
None of these layers require the same HTS classification to trigger — a product's 8-digit subheading determines Section 301 exposure, while AD/CVD scope is determined by the written scope language of the specific order, which can turn on product description details a plain classification review wouldn't catch. Getting the classification right and checking AD/CVD scope are two separate steps, not one.
Why This Keeps Catching People
The mechanism itself isn't complicated — the surprise is almost always that someone assumed only one of these layers applied, or assumed they cancel each other out somehow. They don't. A product on the Section 301 list and inside the scope of an AD/CVD order pays the MFN rate, then the Section 301 rate, then the AD rate, then the CVD rate, each calculated against the same full customs value. A sourcing decision made on a landed-cost model that only accounts for MFN can be off by a factor of two or more before the shipment ever reaches a port.
If a landed cost model only has one duty line item, it's missing the layers that actually matter for a meaningful share of current imports. Section 301 and AD/CVD exposure need to be checked before a sourcing decision is finalized, not discovered on the entry summary.
How Declaro Reads This
Getting the classification right is the input every one of these layers depends on — the 8-digit subheading determines Section 301 exposure, and the product description determines whether an AD/CVD order's scope actually applies. Declaro's classification tooling, built against 220,000+ CBP CROSS rulings, is designed to surface that exposure at the classification step, not after a shipment has already landed.
Declaro helps importers see the real duty stack before it becomes a landed-cost surprise. See how it works →