Add an extra business activity to your company (IAE in AEAT and, if needed, change of objeto social)

What you need to have to hand

1. Certificado digital de representante or Cl@ve of the administrator with apoderamiento in AEAT.
2. Estatutos vigentes and escritura de constitución to review the objeto social.
3. Details of the new activity: epígrafe IAE, start date, address and IVA regime (general, exempt, recargo, etc.).
4. If there’s a local, have the contrato de alquiler and referencia catastral ready.
5. If needed, board resolution and escritura de modificación of the objeto social for the Registro Mercantil.

Documentation

• Company identification (NIF) and the signatory’s ID (DNI/NIE).
• Estatutos and, if applicable, escritura de cambio de objeto social entered in the Registro Mercantil.
• Powers if the signer isn’t the administrator.
• Correct epígrafe IAE and a description of the activity.
• Premises data (full address and square metres) if there is a local.

Step by step

1. Check the objeto social: go to https://sede.registradores.org and request a nota simple or copy of the estatutos from the Registro Mercantil. If the activity fits, you’re good.
2. Change the objeto if needed: approve it in a junta, sign at the notary and have the escritura sent to the Registro Mercantil. Until it’s inscribed and published in the BORME, don’t touch the AEAT.
3. Census modification at AEAT: access https://sede.agenciatributaria.gob.es/Sede/procedimientos/G322.shtml and log in with Cl@ve or certificado. Mark Modificación and select Alta de nueva actividad.
4. Fill Actividades y Locales: enter epígrafe IAE, start date, address and IVA regime. If you’ll apply retenciones, tick that box.
5. Submit and save the receipt: download the PDF with CSV. Banks, clients or administrations will ask for it.
6. Optional in-person route: if you prefer the counter, book cita previa at https://sede.agenciatributaria.gob.es/Sede/cita-previa.html and take the completed 036 with your documents.

Tips that save you time

• Don’t guess the epígrafe IAE: find the right one in the Tarifas del IAE (RDLeg 1175/1990). A wrong epígrafe complicates IVA and withholdings.
• Apoderar before using Cl@ve: the Registro de Apoderamientos in the AEAT saves you a trip. Without apoderamiento you can’t file for the company.
• You won’t upload estatutos, but have them: the 036 won’t force attachments, but Hacienda can request them later. Keep them ready.
• Decide the IVA regime beforehand: if you change regime (or prorrata affects you), decide before filing. Changing criteria later is another 036 and sometimes has strict deadlines.

Common mistakes that can derail the process

• Missing the one-month window from when you start the activity: fines and hassle.
• Not changing the objeto social when needed: the Registro will block operations later and they may contest deductions.
• Picking the wrong epígrafe IAE: you might be put in an IVA or retention regime that doesn’t apply.
• Forgetting to declare the premises: if there’s a local and you don’t declare it, you’ll need another modification.
• Trying with Cl@ve without apoderamiento: the AEAT site will error out and you’ll waste time. Better a representative certificate or have the apoderamiento in place.