Vietnam’s headline US reciprocal tariff is 20%. The effective rate Vietnamese exporters actually pay on US-bound shipments rarely lands at that number. The gap between the headline figure and the effective rate is the kind of detail that surfaces in tariff-advisory client alerts and customs broker briefings but stays mostly absent from the broader business press coverage. For an ASEAN operator planning the next four quarters of US-bound shipments, the gap matters. The effective tariff is the cost line that appears on the invoice; the headline tariff is the framing that appears in the policy commentary.

The reciprocal tariff is the US policy framework introduced through 2025 and 2026 that sets a country-specific tariff rate on imports from each major trading partner. Vietnam’s rate of 20% sits inside this framework. The framework is one of several US tariff systems that apply simultaneously to imported goods. The others include the Most Favoured Nation (MFN) tariff schedule, the country-specific Section 301 tariffs (originally applied to China), the Section 232 national security tariffs on steel, aluminium, autos and semiconductors, and various product-specific anti-dumping and countervailing duties. The arithmetic question for any specific shipment is which of these tariff lines apply, and whether they stack on top of each other or replace one another.

The Section 232 exemption framework is the one with the largest dollar impact on Vietnamese exporters. Section 232 of the Trade Expansion Act of 1962 authorises the US president to impose tariffs on imports deemed a national security risk. The Trump administration has used Section 232 to apply tariffs on steel and aluminium imports (most countries face 25% on steel and 10% on aluminium), on imported autos and auto parts (currently 25%), and on semiconductors and related products (rates vary by product and country). According to guidance issued by US Customs and Border Protection and analysed by international law firm Hunton Andrews Kurth, the reciprocal tariff does not stack on top of Section 232 tariffs. A Vietnamese auto parts exporter pays the 25% Section 232 rate on its US-bound shipments. The 20% reciprocal rate does not stack on top; the Section 232 treatment supersedes the reciprocal calculation for goods in covered categories.

The exemption framework extends to several other categories under separate executive orders. The US Trade Representative’s reciprocal tariff guidance explicitly exempts pharmaceutical goods from the reciprocal rate; pharmaceuticals are treated under their own duty schedule. Aviation parts and equipment are exempt under aviation-specific arrangements. Certain industrial inputs and minerals are exempt under critical-supply-chain considerations. Various agricultural products were added to the exemption list through subsequent executive orders, with the most recent addition in November 2025 covering several agricultural categories. Each exemption removes a slice of the export book from the reciprocal calculation.

The product-mix arithmetic for a Vietnamese exporter therefore depends entirely on what they ship. A Vietnamese textiles and apparel exporter, with no Section 232 exposure and no exemption category coverage, pays the full 20% reciprocal rate on US-bound shipments. A Vietnamese auto parts exporter pays 25% on covered parts under Section 232 and falls outside the 20% reciprocal calculation entirely on those parts. A Vietnamese pharmaceuticals exporter operates under the pharmaceuticals exemption and faces a different duty calculation entirely. A Vietnamese semiconductor manufacturer, where applicable, sits under the semiconductor-specific Section 232 treatment. The weighted-average tariff for Vietnam’s total US-bound export book is therefore lower than 20%, but the specific exporter’s effective rate depends on which categories make up its shipment mix.

Three operational implications follow for ASEAN shippers. The first is product-mix audit. An exporter that has been pricing its US-bound product on the assumption of a 20% tariff add-on may be over-pricing or under-pricing depending on its Section 232 and exemption exposure. A clean product-mix audit, run by the company’s customs broker or trade counsel, surfaces the actual effective rate by category. The second is contract architecture. Buyer-side US importers are increasingly writing supply contracts with tariff-pass-through clauses that distinguish between reciprocal tariff rates, Section 232 rates and exemption categories, rather than treating tariffs as a single line. ASEAN suppliers signing those contracts need to understand the architecture to negotiate against it. The third is product-mix planning. The exemption framework creates strong incentives to shift product mix toward exempt categories where possible, although the operational cost of doing so usually exceeds the tariff savings unless the shift was already on the production roadmap for other reasons.

The framework is also a moving target. The reciprocal tariff guidance has been updated multiple times since its introduction, with several exemption categories added through 2025, and the list of countries covered under specific reciprocal rates has been revised in step, with Vietnam’s rate the subject of continuing bilateral negotiation. A Vietnamese exporter doing a product-mix audit in June 2026 should expect the calculation to shift again by year-end as further rulings, exemptions and rate changes work through the executive order process.

For an ASEAN operator briefing the executive committee on tariff exposure, the honest answer is that the headline rate is the wrong number to cite. The right number is the product-mix-weighted effective rate, calculated against the current exemption framework with explicit assumptions about Section 232 coverage by category. That calculation requires the company’s actual customs data, drawn from the firm’s own shipment records rather than from broader policy commentary.

The exporter-side reality is that this uncertainty translates directly into commercial risk. A Vietnamese exporter that has priced its contracts on the 20% headline rate is either absorbing an unrecovered cost or over-charging a US buyer that will eventually reprice. Either outcome damages the commercial relationship. The practical response is contract architecture: multi-year supply agreements need variable-tariff clauses that spell out who bears the cost of a Section 232 rate change, a reciprocal rate revision or a new exemption ruling, and that specify how the pass-through is calculated when the effective rate shifts mid-contract. Exporters signing US supply agreements in the second half of 2026 without these clauses are underwriting a policy risk their customers understand and their own boards typically do not.

When the next round of US Trade Representative guidance lands, the question for Vietnamese exporters is which of their product categories moves into or out of the exemption framework, and how the recalculated effective rate compares to the headline rate that earnings-call commentary keeps citing.