Add activity or branch (Empresa adicional) at AEAT and Registro Mercantil

What you need

1. Have a representative digital certificate working (for companies it's the most reliable). Cl@ve sometimes won’t let you sign the 036.
2. Know the exact epígrafe IAE of the new activity and the start date.
3. If you’ll open a sucursal, you need the company agreement and to go to notary.

Documentation

• NIF and razón social as shown in the Registro Mercantil.
• Escritura y estatutos (PDF) if you will register a sucursal.
• Address of the premises and referencia catastral (if there’s a physical premises).
• Rental contract or title deed of the premises (if applicable).
• Tax details of the activity: IVA regime, withholdings and reporting obligations.
• Acuerdo/junta to open the sucursal (if applicable) and representative’s details.

Step by step

1. Go to sede.agenciatributaria.gob.es > Censos > Modelo 036/037 (modification) with your certificate.
2. In Modelo 036, tab Actividades y locales, press Alta and enter: epígrafe IAE, start date, address of the premises, surface and characteristics if requested.
3. Check IVA (Modelo 303), withholdings, and obligations (390, 349, etc.). Adjust periodicity according to your volume.
4. Sign and submit. Download the justificante. The registration takes effect immediately.
5. If you are not exempt from IAE (cifra de negocios ≥ 1.000.000€), file Modelo 840 in the mes siguiente to the start. The cuota is municipal and variable.
6. If it’s a sucursal: execute the escritura at a notary (opening of branch, representative details and address) and file at the Registro Mercantil provincial (telematic at sede.registradores.org or in person). Pay aranceles.
7. Once the sucursal is registered, return to Modelo 036 to reflect the premises/sucursal (if it’s a foreign branch, use its NIF assigned by AEAT; if it’s a Spanish company, same NIF).

Tips

• Check the epígrafe IAE before submitting. Changing it later means another modification and possible trouble with IVA.
• If you invoice intracommunity operations, enable the ROI (registro de operadores intracomunitarios) in the 036.
• Keep a folder with PDFs of the 036 justificantes and, if applicable, the nota de inscripción from the Registro. Banks and suppliers will ask for them.
• If the 036 doesn’t load, try Chrome/Firefox and clear cache. Avoid Safari.

Common mistakes

1. Start invoicing without registering the activity: typical €200 sanction and IVA issues.
2. Confusing local adicional with sucursal: the first is just 036; the sucursal needs escritura and inscripción in the Registro Mercantil.
3. Forgetting Modelo 840 when you’re not exempt from IAE: the deadline is 1 mes from the start.
4. Submitting with Cl@ve for a company and getting stuck: use certificado de representante.
5. Not updating IVA periodicity and withholdings in the 036: requisitions come later and you’ll have to correct retroactively.