IMMEX Regime Change (F4 / F5) vs. Regularization (A3) in Mexico: Complete Tax & Customs Guide

Not every component or machine imported temporarily into a Mexican IMMEX plant ends up being exported back to the United States. Every manufacturing operation eventually encounters four practical situations:

1. A Mexican domestic customer wants to buy a batch of your finished goods (or your recyclable metal scrap) inside Mexico without a virtual V1 transfer.
2. Slow-moving raw materials (IN or V1) are approaching their 18-month or 6-month retention deadline, and you need them to stay in your Mexican warehouse legally without shipping them back across the border.
3. You decide to keep or sell a 5-year-old CNC machine or injection press (AF) permanently in Mexico.
4. During an internal Anexo 24 reconciliation, you discover an old IN or V1 pedimento whose 18-month or 6-month clock already expired last quarter, and you must cure the violation before SAT sends an audit notice.

In Mexico’s customs system (Appendix 2 of Anexo 22), those four scenarios are resolved without moving a single truck to the border by filing one of three specialized pedimento keys: F4, F5, or A3.

1. Executive Comparison: F4 vs. F5 vs. A3

Choosing the wrong pedimento key, for example, trying to file an F4 on an already-expired IN pedimento, causes an immediate rejection by the customs broker’s SAAI validator or inside SAT’s SCCCyG (Anexo 30/31):

2. How F4 Works for Raw Materials, Domestic Sales, and Scrap (Article 109 & Rules 1.6.7–1.6.9)

Under Article 109 of the Mexican Customs Law and RGCE Rule 1.6.7, an IMMEX company may convert temporary inputs (IN or V1), either in their original state or already incorporated into finished products, into definitive imports by filing an F4 pedimento before their permanence clock expires.

Three High-Value Operational Rules for F4 Filings:

1. Tariff Rate & Preferential Treaties (Rule 1.6.8):
   • When filing an F4, you do not have to pay the general MFN tariff if the inputs qualify for a 0% preferential rate under USMCA (TL), another Mexican Free Trade Agreement, or your company’s active PROSEC registration (PS) / Regla Octava permit (RO) in effect on the date of the F4 or original entry.
2. Consolidated Monthly F4 Pedimentos:
   • If your plant sells a recurring percentage of finished goods to domestic Mexican customers (while still maintaining your statutory IMMEX export threshold and mindful of Maquiladora Safe Harbor Art. 181 rules), you can open a monthly consolidated F4 pedimento to convert all temporary BOM components contained in that month’s domestic sales in a single monthly customs closing.
3. Selling Industrial Scrap & Waste Locally (Desperdicios: Article 109 & Rule 1.6.9):
   • When your plant sells metal turnings, copper wire offcuts, or plastic runner scrap generated from temporary IN materials to a local Mexican recycler, you must first file an F4 change of regime.
   • Crucially, under Article 109 (Third Paragraph) of the Customs Law and RGCE Rule 1.6.9, when changing the regime of industrial waste (desperdicios), the tariff classification and customs value used on the F4 are not the original prime raw material classification and value, they are the tariff fraction and commercial scrap value in the physical state in which the waste sits at the time of the F4 (typically 0% IGI as metal/plastic scrap and 16% VAT on the low scrap sale value), while discharging the full original UMT weight from Anexo 24 and Anexo 30/31.

3. How F5 Works for Machinery & Fixed Assets: The Article 110 Depreciation Shield (Rule 1.6.10)

Suppose your Mexican plant imported a $1,000,000 USD CNC machining center 6 years ago on a temporary Fixed Asset pedimento (Clave AF). Today, you want to sell that machine to a Mexican buyer or convert it to definitive import status (Clave F5) so it is no longer tied to your IMMEX program.

Do you have to pay import duty and 16% VAT on the original $1,000,000 USD value from 6 years ago? No.

Under Article 110 of the Mexican Customs Law and RGCE Rule 1.6.10, when converting temporary machinery and equipment (AF) to definitive import status (F5), the importer is legally entitled to reduce the customs value by deducting the annual fiscal depreciation percentages established in Articles 34 and 35 of the Mexican Income Tax Law (LISR) for every full year elapsed between the original AF temporary import date and the F5 payment date:

Real-World Calculation Example (F5 Machinery Depreciation under Art. 110 LA)

• Original AF Machine Value (Imported 6 Full Years Ago): $1,000,000 USD.
• Applicable Annual LISR Depreciation Rate (e.g., 10% per year for general industrial machinery under Art. 35 LISR): 10% x 6 full years = 60% accumulated depreciation.
• Depreciated Customs Value Basis on the F5 Pedimento:

  $1,000,000 USD x (1 - 0.60) = $400,000 USD

• Tax Savings: Both the General Import Duty (if not already 0% under USMCA/PROSEC) and the 16% cash VAT are calculated on $400,000 USD instead of $1,000,000 USD, reducing the cash VAT outlay from $160,000 USD down to $64,000 USD (while still discharging 100% of the original $1,000,000 USD credit in SCCCyG under Anexo 30/31 rules).

(Note: To claim Article 110 depreciation on an F5, you must hold the complete original AF customs dossier proving the exact entry date and machine serial number).

4. How A3 Regularization Works When Inventory Has Already Expired (RGCE Rule 2.5.2)

What if your compliance team runs an audit today and discovers $250,000 USD of raw materials imported on an IN pedimento 20 months ago (2 months past the 18-month deadline) or on a V1 pedimento 8 months ago (2 months past the 6-month Rubro A deadline)?

Because the statutory permanence period has already expired, you are legally barred from filing an F4. Instead, provided SAT has not yet initiated a formal audit (facultades de comprobación), you cure the illegal stay spontaneously (Article 73 CFF) by filing a Regularization Pedimento (Clave A3) under RGCE Rule 2.5.2:

1. Declare Identifier RE (Appendix 8 of Anexo 22): Links the A3 regularization pedimento to the expired temporary import pedimento (IN or V1) in the Discharge Block (Bloque de Descargos).
2. Pay Updated Duties, Cash VAT, and Monthly Surcharges (Recargos):
   • Calculate the inflation adjustment factor (Factor de Actualización INPC under Article 17-A CFF) from the month of original entry to the month of A3 payment.
   • Calculate monthly interest surcharges (recargos under Article 21 CFF and the applicable annual Ley de Ingresos de la Federación—for example, 2.07% per month for 2026 based on the 1.38% base rate in LIF Art. 11 Fracc. I multiplied by 1.5x, and 1.47% per month for prior fiscal years) for every month elapsed since the tax obligation became due.
   • Pay the 16% VAT and any applicable IGI, DTA, and surcharges 100% in cash (Forma de Pago 0).
3. Comply with Non-Tariff Regulations (RRNA / NOMs): Satisfy any RRNAs applicable on the date of the A3 regularization.
4. Transmit the SCCCyG Correction Discharge Report (Informe de Descargo de Corrección): Once the A3 pedimento is paid and appears in SAT’s SAAI database, upload a Correction Discharge Report in the SCCCyG portal referencing the A3 pedimento to amortize and remove the Expired Credit (Crédito Vencido) from your Anexo 30/31 statement of account.