Add an additional activity to your company (Registro Mercantil + AEAT)

What you need to have to hand

1. Current objeto social (latest registered escritura). 2) Clear decision on what new activity you’ll do and from when. 3) Exact epígrafe IAE. 4) Cl@ve or certificado of the administrator/apoderado. 5) If you must expand objeto social: shareholders’ meeting minutes and a notary appointment.

Documentation

• Escritura de modificación de estatutos with the new objeto social (only if needed).
• NIF de la sociedad and DNI/NIE of the signatory/presenter.
• Justificante de presentación/inscripción from the Registro Mercantil.
• Epígrafe IAE and CNAE of the activity, with the start date.
• Poder de representación or apoderamiento in AEAT if a third party files.
• If you exceed IAE thresholds: data for Modelo 840 (activity address, surface, etc.).

Step by step

1. Check the objeto social. If the new activity fits, you skip notary/registro. If not, call a meeting and agree to expand the objeto social.
2. Sign the escritura at a notary. Ask the notary for precise wording (avoid vagueness that the registrador will reject).
3. File at the Registro Mercantil provincial office (teletrámite at sede.registradores.org or in person). Pay aranceles and keep the asiento de presentación.
4. When it’s inscrito, download the nota simple/inscripción. If no amendment was needed, go straight to the 036.
5. Go to sede.agenciatributaria.gob.es > Censos and submit the Modelo 036 as a modification: add IAE epígrafs, adjust obligations (IVA/IS/retenciones), and enter the start date. Submit and save the receipt.
6. If applicable, process IAE (Modelo 840) at the Ayuntamiento/AEAT depending on the municipality and submit the 848 if requested for cifra de negocios.
7. Update invoices (epígrafe/CNAE), books and, if needed, request licencias municipales or submit a declaración responsable before opening a premises.

Time-saving tips

• Pick the exact epígrafe IAE before going to the notary; it helps draft an objeto social that won’t cause trouble.
• If the company is an S.L. with a sole admin, prepare an apoderamiento in AEAT in case someone else files the 036.
• File the 036 the same day you start invoicing the new activity and forget about the 1-month deadline.
• Use Cl@ve or a certificado and avoid Safari: the AEAT site behaves better with Chrome/Firefox.

Typical mistakes that will mess up the process

• Not changing the statutes when the activity isn’t in the objeto social: Registro won’t chase you immediately, but you may have problems with contracts, banks or licences.
• Wrong IAE epígrafe: later you may be required to pay IVA/withholdings you didn’t expect or lose exemptions. Check it first.
• Missing the one-month deadline to file the 036: expect a census fine.
• Objeto social too generic: the registrador will raise defects and you’ll go back to the notary.
• Forgetting municipal licences if you open premises: even if AEAT and Registro are fine, the Ayuntamiento can shut you down.