Before you register

Confirm your residence permit allows autónomo activityDNV (freelance variant), Entrepreneur, EU Family Member, Arraigo all allow. NLV does NOT.
Choose your IAE activity code(s)Look up your activity in the Impuesto sobre Actividades Económicas tariff. You can register multiple codes if you do several types of work.
Decide your IVA regimeMost autónomos use the general IVA regime (21% standard). Some activities qualify for simplified or exempt regimes. A gestor can advise.
Open a separate Spanish bank account for business use (optional)Not strictly required, but strongly recommended for clean bookkeeping.

Tax Agency registration (Agencia Tributaria)

File Modelo 036 (or simplified Modelo 037)The alta censal — declares your economic activity, IAE code, IVA regime, and tax address. Submit online with digital certificate, or in person.
Confirm your alta is activeYou receive a confirmation document. Keep this for your records and to show clients.

Register with Tesorería General de la Seguridad SocialOnline with Cl@ve / certificate, or in person at a TGSS office. Choose Régimen Especial de Trabajadores Autónomos (RETA).
Select your contribution baseNew autónomos qualify for Cuota Reducida: €80/month for first 12 months (extendable to 24 months if income is low).
Confirm direct debit for monthly contributionsTGSS collects automatically. Contributions are due the last working day of each month.

Issue your first compliant invoiceMust include sequential number, your NIF, client details, tax base, applicable IVA, IRPF withholding (if invoicing Spanish entities).
Set up bookkeepingTrack all income and expenses. Excel works; tools like Quaderno, Holded, or Anfix automate the quarterly filings.
Prepare Modelo 303 (IVA return)Filed quarterly: by January 20, April 20, July 20, October 20.
Prepare Modelo 130 (IRPF advance)Filed quarterly on the same schedule as Modelo 303. Pays 20% of net profit as income tax advance.

File Modelo 390 (annual IVA summary) in JanuaryAggregates the year's Modelo 303 filings.
File Modelo 100 (income tax return, April-June)Your annual Declaración de la Renta. Includes all autónomo income, expenses, and IRPF reconciliation.
File Modelo 347 (third-party transactions) in February (optional)Required if you had any single client/supplier with > €3,005.06 in annual transactions.