Register a second company (SL) and its NIF: Registro Mercantil + AEAT

What you need to have to hand

1. Cl@ve or certificado digital to sign at the AEAT and, if needed, on the Registradores platform.
2. A company name (and two or three alternatives) to request the certificación negativa.
3. Basic decisions: domicilio social, objeto social, administrators, capital and bank account.
4. A notary you trust who can send the escritura electronically to the Registro.

Documentation

1. Certificación negativa de denominación social from the Registro Mercantil Central.
2. DNI/NIE of partners and administrators; NIF if any partner is another company.
3. Estatutos sociales (if you use estatutos tipo, faster and cheaper).
4. Escritura de constitución (PDF with CSV from the notary).
5. Proof of capital (bank certificate or declaration in the escritura if applicable).
6. Modelo 036 at the AEAT: first for the NIF provisional, then for the NIF definitivo and tax obligations.
7. Proof of payment of Registro and BORME fees.
8. Hoja de titular real for the Registro.

Step by step

1. Reserve the name: go to https://www.rmc.es/Denominaciones, request the certificación negativa and keep it safe. Without it the notary won’t sign.
2. Sign at the notary: bring the certificación and your DNIs/NIEs and decide the management body. If the notary uses CIRCE you’ll save back-and-forth.
3. Get the provisional NIF: with Cl@ve at https://sede.agenciatributaria.gob.es, go to Censos/NIF de personas jurídicas and submit Modelo 036 attaching the copia simple of the escritura. It’s normally issued the same day.
4. Register the company: if the notary doesn’t send it, upload the escritura yourself via the Colegio de Registradores’ electronic filing (https://www.registradores.org/registro-mercantil/). Pay aranceles and BORME publication.
5. Switch to definitive NIF: once you have the inscripción, return to the AEAT and file another Modelo 036 to convert to definitivo and declare IAE, IVA and retentions. Set a realistic start date for activity.
6. Check your NIF card and census data: download the receipt and verify domicilio fiscal and notification methods.

Tricks that save you time

• Estatutos tipo: if they suit you, they speed up the process and cut notary and registry costs.
• Coordinate with the notary: have them send the escritura to the Registro and, if possible, help with the provisional 036. You’ll avoid duplicated steps.
• Pick sensible dates: set the activity start date in the 036 when you actually start invoicing. You’ll avoid filing empty returns and surprises.
• Scan everything with CSV: AEAT and Registro want PDFs with códigos seguros de verificación; it saves you from requests for more documents.

Common mistakes that can set you back

1. Letting the certificación expire: after 3 months it’s no longer valid for the escritura. You’ll need to request another and pay again.
2. Forgetting the NIF definitivo: you’ll be stuck with a provisional NIF and banks or clients may block payments. Once registered, file the 036 and move on.
3. Double filing at the Registro: both you and the notary sending the same thing. Result: two entries and two bills. Talk to the notary first.
4. Invoicing without census registration: fines and surcharges for VAT/retentions. 036 first, invoices after.
5. Platforms that fail: if Registradores throws an error, switch browser or clear cookies. It’s common.