Anexo 24 Really Is: The Inventory Control System That Keeps Your IMMEX Alive

Most IMMEX operators treat Anexo 24 as a filing chore, a report the customs broker produces and the authority files away. That framing is the most expensive misconception in cross-border manufacturing. Anexo 24 is not a report. It is the live, automated inventory control system that proves every temporarily imported input either left the country or was otherwise accounted for. When it holds, the duty deferral that makes your operation viable holds with it. When it breaks, the Servicio de Administración Tributaria (SAT, Mexico's tax authority) can treat your temporary imports as if they were never returned, and the arithmetic that follows is not small.

This is the explainer we wish every new IMMEX operator read before their first temporary import, not after their first audit notice.

What Anexo 24 actually is

Anexo 24 is the annex to the Reglas Generales de Comercio Exterior (RGCE, Mexico's General Foreign Trade Rules) that defines the minimum content of the automated inventory control system every IMMEX company must run. Its legal spine sits in two places: Article 59, fracción I of the Ley Aduanera (Mexico's customs law), which obliges any importer to keep automated inventory control with a permanently current record of foreign-trade goods, and Article 24, fracción IX of the Decreto IMMEX, which ties that obligation directly to the program.

Operators usually call the system the SACI (Sistema Automatizado de Control de Inventarios). Companies holding the IVA/IEPS certification run a stricter version, the SECIIT, whose data is pulled electronically and cannot be edited by hand. Whatever the label, the SAT published the current specification as the Anexo 24 de las RGCE para 2026, so this is a live, versioned requirement, not a legacy formality.

One distinction saves operators a great deal of confusion: Anexo 24 is not Anexo 31. Anexo 24 controls the physical inventory of temporarily imported goods. Anexo 31 controls the IVA and IEPS credit and guarantee accounts tied to certification. They are separate systems with separate failure modes, and passing one does not cover the other.

How the system actually works

The RGCE require the Anexo 24 system to do three things: comply fully with the Ley Aduanera, its regulation, and the RGCE on temporary-import inventory control; provide an instrument to verify returns and track goods still pending return; and generate the reports the authority can demand at any time.

To do that, the system carries a fixed set of catálogos (reference tables) and módulos (transactional modules). The catálogos identify the taxpayer, the materials used in production, the finished products, the suppliers and clients, any submanufacture or submaquila, and fixed assets. Each material and finished product carries its fracción arancelaria (tariff classification) and its unit of measure under the TIGIE (Mexico's tariff schedule). The módulos then record the movement: customs entries for temporary imports, the materials consumed, and the exits, meaning returns abroad, destructions, donations, régimen changes, or definitive imports.

The logic that matters is the descargo (discharge). A temporary import opens when the pedimento (Mexico's customs declaration) enters it into the system. It stays open, drawing down against your bill of materials as production runs, until it is discharged by a return, a transformation-and-export, a régimen change, or a definitive import with duties paid. Every open temporary import is a clock, because the Ley Aduanera sets permanence windows on how long goods may stay under the program before they must be discharged. An input never discharged inside its window is the single most common finding in an inventory audit.

To make the abstraction concrete, follow one lot of imported resin through the system:

1. The resin enters on a temporary-import pedimento, which opens the lot in the entries module against its fracción arancelaria and quantity.
2. As production runs, the system draws that lot down against the bill of materials for each finished good, recording how much resin each unit consumed, plus mermas (process waste) and desperdicios (scrap).
3. When the finished goods are returned abroad on an export pedimento, the system discharges the corresponding resin, closing the loop.
4. Any resin not consumed or returned inside its permanence window has to be discharged another way, by régimen change or definitive import with duties paid, or it becomes an open exposure.

The elegance is also the trap: the loop only closes if every step is recorded accurately and on time. One untracked scrap rate or one late export entry leaves resin "open" in the system that physically left the plant months ago.

Here is what changed, and why 2026 raised the stakes. The customs reform published in the Diario Oficial de la Federación (DOF, Mexico's federal gazette) on November 19, 2025, in force January 1, 2026, now requires inventory control systems to be permanent and interoperable with the customs electronic system, with continuous remote access for the authority.

On paper, the obligation to keep automated inventory control has existed for years. In practice, what changed in 2026 is that the SAT no longer has to wait for an audit to look. The system now has to be permanent and interoperable, which turns the authority's view of your discharges from a snapshot on request into a continuous window.

Common mistake. Reconciling Anexo 24 once a month and calling the inventory controlled. The reform's standard is a permanently current system, not a month-end catch-up. A discharge that is correct on the 30th but wrong for the preceding twenty-nine days is still an exposure the authority can now see.

Why it decides your audit

The consequence chain is what makes this an executive concern, not a back-office one. If the system cannot demonstrate that a temporary import was returned or otherwise discharged, the SAT can determine that the goods were, in effect, definitively imported. That determination triggers the retroactive Impuesto General de Importación (IGI, the general import duty) that was deferred, plus the Impuesto al Valor Agregado (IVA) that, without certification, was never exempt to begin with, plus recargos (surcharges) and inflationary updating.

Then comes the penalty, and here the 2025 reform bites. Article 178, fracción III of the Ley Aduanera now carries a fine of 250% to 300% of the commercial value of the goods for the temporary-import infractions it covers, raised from the 70% to 100% range that applied before the reform. A separate provision, Article 185-A, sanctions the failure to keep the automated inventory control system itself. And beyond any single fine sits the existential risk: suspension or cancellation of the IMMEX program and removal from the Padrón de Importadores (the importers' registry), which stops the operation from importing at all.

In our work across the corridor, the pattern is consistent: clearance problems that look like a broker issue are usually an inventory-control issue upstream. Across more than 190,000 customs operations a year at 39-plus ports, the operations that pass a SAT review without disruption are the ones whose Anexo 24 was already current the day before the review landed, not the ones who tried to rebuild it the week the notice arrived.

Five misconceptions that turn into holds

The first is that Anexo 24 is the customs broker's job. The obligation is the importer's, written into Article 59 of the Ley Aduanera. The broker supports it; the liability stays with you. After the 2025 reform widened the broker's own exposure to responsabilidad solidaria (joint and several liability), scrutiny rose on both sides of that relationship, not just yours.

The second is that monthly reconciliation is enough. It was a defensible habit before 2026. Against a permanent, interoperable standard, it is a gap.

The third is that a cleared pedimento means the import is safe. Clearance is only the opening entry. The risk lives in the discharge, which happens months later, and which the pedimento says nothing about.

The fourth is that a clean ERP equals a clean Anexo 24. Your ERP tracks value and accounting. Anexo 24 tracks customs discharge against the pedimento and the bill of materials. The two diverge in normal operations, and that divergence is precisely what an audit surfaces.

The fifth is that Anexo 24 and Anexo 31 are interchangeable. They are not, as covered above, and treating them as one leaves half your exposure unmanaged.

Quick check. Pull your three oldest open temporary imports. For each, can you show the pedimento that opened it and the document that discharged it, whether a return, a destruction, a régimen change, or a definitive import? If any is open past its permanence window with no discharge on record, that is the first thing an audit finds, and now the first thing a continuous system exposes.

When to bring in a broker to audit it

A full Anexo 24 review earns its cost at specific moments: after rapid IMMEX expansion, after an ERP migration, after a change of customs broker, after an acquisition, or simply when more than twelve months have passed since anyone reconciled the system against what the SAT actually expects. A serious review looks for open temporary imports past their windows, mismatches between bill-of-materials consumption and recorded discharges, gaps in the catálogos, and missing discharge documentation. Those are the findings that, left alone, become retroactive assessments.

Anexo 24 is not paperwork the SAT files away. It is the operational backbone of the duty deferral that makes your manufacturing viable, and since 2026 it is a system the authority can watch continuously rather than inspect occasionally. Treat it as infrastructure, not as a report. If your last full reconciliation is more than a year old, that is the review to run before the SAT runs it for you. Talk to a Joffroy expert about an Anexo 24 audit-readiness review for your operation.

TRADE. UNDER CONTROL.

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