Are the CRU and the IDUFIR the same thing?

In practice yes: the CRU (Código Registral Único) is the current name and replaces the IDUFIR, created in 2008. Forms and the Registrars' own e-office treat them as the same identifier, the property's national ID.

Do all properties have a CRU?

Registered properties are progressively incorporating the code, but not every older property has it assigned or visible on old documents. If it does not appear, the property is identified by its complete registry details.

Where do I see my home's CRU?

In a recent escritura, in a previous nota simple or certificate, or by asking at the Land Registry. You can also locate the property by address on the Registrars' Geoportal and obtain its data from there.

Can I search a nota simple with just the address?

Yes, the e-office and the Geoportal allow it, but it is not always enough to identify the exact unit: outdated addresses or buildings with many units can give ambiguous results. With the CRU/IDUFIR or registry details, identification is direct.

Finca registral, CRU and IDUFIR: a property's identifiers at the Spanish Land Registry

The finca registral: the property's number at its Registry

Every property registered at the Spanish Land Registry (Registro de la Propiedad) has a unique finca number within its Registry office. Spain has hundreds of Land Registry offices (large cities have several), so the finca number only identifies the property in combination with the specific office: "finca 12,345" exists in many Registries at once.

That is why a property's complete registry details are always four: province, municipality, Land Registry office and finca number. They appear in the escritura and in any previous nota simple or certificate.

CRU and IDUFIR: the property's national ID

To avoid ambiguity between Registries there is a unique national identifier:

The IDUFIR (Identificador Único de Fincas Registrales) was created by the College of Registrars in 2008.
The CRU (Código Registral Único) is its current name: according to the Registrars' own e-office, the CRU replaces the IDUFIR, with the ambition of being like the property's DNI (Spanish national ID).

In practice you will see both names used together ("CRU/IDUFIR") in forms and documents. It appears on notas simples, certificates and recent escrituras, and the e-office lets you search a property's information directly by this code.

CRU and IDUFIR are not the referencia catastral

This is the most frequent confusion. The Registrars' e-office states it literally: the CRU/IDUFIR does not correspond to the referencia catastral. They are codes from different systems:

CRU/IDUFIR and finca registral: from the Land Registry (ownership and charges).
Referencia catastral: from the Catastro (the property's fiscal description, 20 characters).

Where to find these identifiers

In the purchase escritura: the complete registry details usually appear in the property description, and the CRU/IDUFIR in recent documents.
In a previous nota simple or certificate: they always include the finca number, the Registry and, where it exists, the CRU/IDUFIR.
By asking at the Land Registry office of the municipality, with the address or the owner's name.
Through a nota de localización at the e-office, when you only have partial data. Bear in mind this report is billed even if the result is negative.

Why requesting with the exact identifier matters

Requesting the nota simple by CRU/IDUFIR or by complete registry details eliminates localisation errors: no wrong properties, no confused units within the same building, no failed localisation reports being billed. If you request by address and the building has many units (or a penthouse not differentiated in the listings), the exact identifier is the guarantee that the document you receive is for your property.

Where to find each identifier

Registry property number (finca registral): appears on the nota simple itself, on registry certificates and is usually quoted in the purchase deed. It is a number assigned by the Land Registry of the district.
IDUFIR: assigned by the Registry when the property was added to the computer system. It appears on recent notas simples and certificates.
CRU (Código Registral Único): since 2008 it has replaced the IDUFIR as the national unique identifier. In practice, documents refer to "CRU/Idufir" as if they were the same thing, because the CRU took its place.
Cadastral reference (referencia catastral): not held by the Registry but by the Catastro (IBI tax receipt, cadastral record, Catastro e-office). It does not correspond to the others, as the Registrars' association itself warns.

Example: reading a purchase deed

If you have the deed at hand, look for the property description section. You will normally find something like "finca registral number 12.345 of Land Registry No. 6 of Madrid", and in more recent documents also the CRU/IDUFIR. With either of those two details, requesting a nota simple is immediate: you enter the identifier and the Registry locates the property with no need for an address.

If the deed is old and shows no identifier, that is fine: the full address (street, number, floor, door and municipality) also works to locate the property.

When the CRU/IDUFIR is needed

When requesting notas simples or certificates online: it is the most direct route and avoids location errors.
In procedures that cross data between administrations (certain grants, licences or taxes), where the form may ask for it.
When checking a property before buying: if the seller gives you the CRU, you can verify yourself that the property being shown is the same one that is registered.

Common mistakes

Requesting a nota simple "by cadastral reference" expecting the Registry to accept it as a registry identifier: they are different systems.
Confusing the Registry office number (No. 1, No. 2... of each municipality) with the property number.
Assuming a home is always a single registry property: a flat, its storage room and its parking space can be separate registry properties, each with its own identifier.