Mexico's Electronic Value Declaration: October 1, and the Liability That Already Changed

October 1 is the date in every customs alert this month. The change that will still matter a year from now happened on January 1.

On October 1, 2026, Mexico's Manifestación de Valor becomes a transmitted electronic filing. Form E2, through the single window, for every party bringing goods into Mexican territory. The current date arrived on July 31, when SAT and ANAM announced that importers may keep complying under the prior scheme through September 30.

That much is in every alert. The part worth ten minutes is what the filing now attaches to.

What October 1 actually requires

The obligation itself is old. Importers have been required to hold a value manifestation for years, documenting the elements that make up customs value: the price actually paid, assists, royalties, commissions, and transport. The obligation sits on the importer under Article 59, fraction III of the Ley Aduanera, and the 2025 reform left that provision alone.

What changes is the method. A document held in a binder becomes a filing the authority receives, stores, and can line up against the pedimento, against the classification you declared, and against every value you transmitted before it.

For a Mexican subsidiary importing from its own parent, that has a specific consequence. The value declared at the border and the transfer price the tax file defends become the same number, transmitted and retrievable. Companies that keep customs and tax on separate desks find out on the first review that the authority no longer has to ask twice.

The liability change that already happened

Here is the part most coverage has backwards, including some written for foreign executives.

The customs reform published in the DOF on November 19, 2025 and in force since January 1, 2026 repealed the exclusions of liability in Article 54 of the Ley Aduanera. Those exclusions protected the customs broker, not the importer. One of them applied where the declared value came in under the transaction value of identical or similar goods by less than 40 percent, and it is gone.

Article 54 now reads as a single paragraph holding the agente aduanal and the agencia aduanal responsible for the truthfulness and accuracy of the data supplied. Article 53, fraction II keeps them as jointly liable parties. No exclusion is available, including where the inaccurate information came from the importer.

Read what that does to the relationship. Your broker now carries the same exposure you do on the same declared value, and has no way to disclaim it. The practical effect arrives as a broker asking for intercompany agreements, royalty terms, and assist detail they never requested before. That request is a counterparty pricing its own risk, and the companies that treat it as a document-gathering exercise in September rather than an argument in October come through this cleanly.

The cost of getting it wrong moved at the same time. Article 184-B, fraction I now carries a fine of MXN 53,500 to MXN 106,970 for inexact or false data on the value of imported goods, replacing the MXN 29,420 to MXN 49,050 range that applied through 2025. An inexact value manifestation is sanctioned separately under Article 185, fraction II.

The extension is real, and it is not in the DOF

This is the detail that decides how much weight to put on the date.

The September 30 extension came through the Third Anticipated Version of the Second Resolution of Modifications to the Reglas Generales de Comercio Exterior 2026, released on the SAT portal on July 31, 2026, amending the Décimo Primero Transitorio of the RGCE 2026 that was published in the Diario Oficial on December 27, 2025.

As of August 18, 2026 that resolution has not appeared in the Diario Oficial. SAT's own normatividad page still lists the Second Resolution only under anticipated versions. This does not make the date unusable. Under regla 1.1.2 of the RGCE, the benefits in an anticipated version apply from the day they are made known on the SAT portal, which is why every serious firm is advising clients to rely on September 30.

It does mean the text everyone is building against is not yet final. Anything introduced when the resolution reaches the DOF lands with very little room before October 1, and the companies holding margin for that are the ones treating the readiness work as due in September rather than in the last week.

Two dates that keep getting merged

September 30 and December 31 are doing different jobs, and conflating them is the most common error in circulation.

September 30, 2026 is the last day to keep complying under the prior scheme. December 31, 2026 is when two temporary documentary facilities expire. The first is the option to file Form E15 reporting only the general data of your contracts under a sworn statement, in place of transmitting the contracts themselves. The second relieves you from transmitting the documentation in Article 81, fractions II, III and IV of the Regulation where it already goes through under Article 36-A.

One point on E15 circulates in reverse, and the reversed version produces a non-filing. Annex 1 requires E15 to be transmitted through the single window together with Form E2. The facility is the contract summary, not an exemption from the window. The contracts themselves still have to be retained and produced on request.

The wider direction

This deadline belongs to a pattern rather than sitting on its own. Mexican customs administration has been moving onto digital rails through 2026, and the shape of the changes is consistent: obligations that are explicit, dated, and identical for every participant, with status consequences attached to filings.

The IMMEX suspension list published in June worked the same way, naming more than 400 program holders and giving each of them a dated, curable path back. The value declaration follows the same logic. The obligation is knowable years ahead, the transition has been paced deliberately across several extensions rather than forced, and the requirement lands on everyone at once.

For a company still weighing a Mexican footprint, the useful read is structural. Importing into Mexico carries a per-transaction filing rhythm that someone has to own by name. Building that into the operating model and the entity in year one costs a fraction of what it costs to retrofit, and it is the difference between a border that is predictable and one that is not.

The bottom line

October 1 converts the value declaration into a filing. January 1 already made your broker jointly liable for what it says, with no exclusion available, and roughly doubled the fine for getting the number wrong. Between now and September 30 the useful work is not watching the date. It is agreeing with your broker, in writing, on how intercompany value, royalties, and assists will be declared, and confirming that your customs file and your transfer pricing file describe the same transaction.

Calder & Vale advises Canadian and US companies entering and operating in Mexico on entity structure, on site and incentives through direct relationships with the state economic development ministries, and on customs and origin exposure, convening the legal and trade work in one room. The companies that carry these obligations well are the ones that decided who owns them before the date arrived.