Guides · Updated August 25, 2026

What a previo is and what it is for

In Mexican customs slang, doing a previo means going to look at the goods with your own eyes before you declare them. The formal name is reconocimiento previo, or examen previo de mercancías, the prior examination of goods. It is a physical review carried out while the cargo sits in customs custody, before the pedimento (the Mexican customs declaration) is drawn up and transmitted. It sounds like an optional piece of paperwork, and technically it is, but it is the difference between declaring what you actually have and declaring what you assumed you had.

What the law says

The legal basis is Article 42 of the Mexican Customs Law (Ley Aduanera), which in substance says that if the party who must prepare the pedimento does not know the characteristics of goods held in customs custody, they may examine them for that purpose. Short wording, and it draws the boundaries clearly:

• It is a right, not a requirement. Nobody will demand a previo of you. You do it when it serves you.
• It applies to goods already in customs custody, meaning arrived and sitting in the bonded facility, not still on the vessel or in transit.
• Its purpose is accurate declaration. It is not a licence to handle the cargo freely: it is an examination to learn what the paperwork does not tell you.

A previo is not a reconocimiento aduanero

The two get confused because the names are close, but they are opposite operations. The previo is yours, by your own decision, before you declare. The reconocimiento aduanero is the authority's physical inspection, after the traffic light turns red, and you do not choose it. One is preparation, the other is an exam. What happens in the second one is covered in what to do when you get a customs inspection.

Who performs it and where

In practice it is carried out by the customs broker (agente aduanal) or one of their registered employees, acting on the importer's behalf, inside the bonded facility (recinto fiscalizado) where the cargo is stored. Anyone entering needs a valid customs identification badge (gafete) for that specific port: the facility will not let someone walk in just because they own the freight. There are also private surveyors and inspection companies that run the previo and hand back a photo report.

As the importer you can attend, and it is worth doing when the open question is technical and the person who understands the product is on your side rather than the broker's. If you go, go prepared: commercial invoice, packing list, spec sheets, and any supplier photos worth comparing against what gets opened.

What actually gets checked

A previo done properly is not a walk-through. It is a checklist against the paperwork:

• Quantities and packages: does the physical count match the packing list.
• Description and nature of the goods: material, composition, use and presentation, which is what feeds the tariff classification.
• Brands, models and serial numbers, where the goods carry them. On equipment and machinery this is the single most commonly misdeclared field.
• Country of origin and labeling, including compliance with Mexican commercial labeling rules where they apply.
• Physical condition: damage, shortages, wet or badly stowed cargo. This is where you photograph everything for the insurance or supplier claim.
• Surprises: goods not on the invoice, samples tucked into a carton, packing material that turns out to be regulated.

Samples that genuinely have to be taken in advance

There is one case where getting ahead of it stops being optional. Article 45 of the Customs Law provides that when a customs inspection requires taking samples of sterile, radioactive or hazardous goods, or of goods that need special facilities or equipment to sample, importers, exporters and customs agencies must take those samples beforehand so they can be presented at the time of the inspection. There is also a registry with the SAT that exempts you from presenting them. If your goods fall into that bucket and you did not prepare it, you will not be improvising on the day the light turns red.

What it costs in time and money

The money cost varies by facility and by port. There is normally a charge for positioning the container, opening and resealing it, sometimes a forklift or yard labor, and the bonded facility bills it against its own tariff schedule. Anyone quoting you a single nationwide figure is guessing. Ask your broker for the breakdown before authorizing it.

One detail works in your favor. During the free storage and custody window at the bonded facility, which for imports is two calendar days, and five at facilities in maritime traffic customs offices, only the handling services and the maneuvers needed for the previo are charged. Schedule the previo inside that window and you are not paying extra storage for the privilege.

The time cost usually matters more. A previo adds a stop to the calendar: the maneuver has to be scheduled, you wait for the facility's turn, and the review happens in business hours. Anywhere from a few hours to a full day depending on yard congestion and the size of the load. That sits on top of the clearance timeline you already have, worth factoring in as we cover in how long customs clearance takes.

When it is worth doing

Some shipments pay for the previo on their own:

1. First import of a new product or from a new supplier. You do not yet know what they shipped or how they packed it.
2. Hard-to-classify goods. Mixtures, parts, textiles, chemicals, equipment with accessories. A wrong tariff code drags duties, non-tariff regulations and penalties behind it.
3. Consolidated or LCL cargo, where your goods traveled mixed with other shippers' and count discrepancies are routine.
4. Suspected damage or shortage. Documenting before clearance puts you in a far stronger position to claim.
5. Goods subject to Mexican standards (NOMs), permits or sector registries, where a missing label stops everything.

At the other end: if you import the same item from the same supplier every week and it has never failed you, a routine previo is cost and delay with no return.

A previo does not save you from the traffic light

Worth stating plainly, because it gets misread often: doing a previo does not lower your odds of drawing red. The automated selection mechanism runs when the DODA is modulated at the gate, and it has no idea whether anyone went to look at the cargo.

What does change is the outcome of a red light. If you get pulled and you already know exactly what is inside, because you counted it and photographed it, the inspection moves fast and clean. If you get pulled while declaring from hearsay, that is where the discrepancies, the administrative proceedings and the lost weeks come from. A previo does not prevent the inspection: it prevents the inspection from finding something.