Laura wants to start providing services on 15 October. She has her DNI (the Spanish national identity card), a bank account and a first client, but she has not yet chosen her epígrafe (the activity heading in the IAE, the Spanish business activity classification) and does not know whether her invoices will carry VAT or withholding. She is not missing just "a piece of paper": before registering she needs to identify the activity, the real start date, the place of work, the tax scheme and an estimate of her profit. With that information, Modelo 036 is filed with Hacienda, the tax office, and she registers in the RETA, the Social Security scheme for the self-employed.
The minimum file before you log in
For an individual, prepare this information and these documents:
| Item | What it is used for |
|---|---|
| A working DNI or NIE | Tax identification and access to the procedures |
| Social Security number | Affiliation and registration in the RETA |
| Bank account with IBAN | Direct debit of contributions and payments |
| An exact description of the activity | Choice of heading and obligations |
| Planned start date | Effective date of the 036 and of the RETA registration |
| Home address and place of activity | Register data, premises and assignment to the business |
| Expected net profit | Provisional contribution bracket |
| Chosen mutua colaboradora | Cover managed together with Social Security |
A mutua colaboradora is a private mutual association authorised to manage certain Social Security benefits, such as sick leave, alongside the public system. If you are a foreign national, knowing the number written on a decision is not enough. The NIE (the identification number for foreigners) must be active in the systems, and your situation must allow you to work on your own account. If you have never been affiliated, you will need to obtain a Social Security number before completing the RETA registration.
To carry out the procedures online you need an accepted means of identification, such as Cl@ve (the government's online identification system), a digital certificate or an electronic DNI, or you can act through a person holding your power of attorney. The Agencia Tributaria also allows certain in-person channels, but the filing must be documented with its receipt.
Decide the activity before ticking boxes
The commercial description does not always match the tax classification. "Consulting" can hide professional services, intermediation, training, software development or the sale of products. Each block may require a different heading and produce different obligations.
Modelo 036 reports all activities and their premises. It also sets up the income tax and VAT schemes, withholdings and special registers. Picking by resemblance the first result from a search engine can leave your invoices carrying a withholding they should not, or leave a quarterly obligation missing.
Before filing, answer:
- what you really sell or which service you really provide;
- who the client is: a business or a private individual, in Spain or abroad;
- where the work is done and from which premises;
- whether you will hire staff or pay rents subject to withholding;
- whether you will buy goods or services before the first sale;
- which date is genuinely the start.
You can put these answers into the self-employed registration form. They are used to prepare both procedures with a consistent date and description.
The tax office: Modelo 036 before you start
The registration return is filed before starting the activities, carrying out transactions or the obligation to withhold arising. For Hacienda, the start is not necessarily the first invoice: it can happen when you acquire goods or services, make collections or payments, or hire staff with the aim of taking part in production or distribution.
Modelo 037 has been abolished since 3 February 2025. Registrations, changes and deregistrations go through the 036, with assistance tools such as Censos WEB when the case fits. If you were already on the register and add another activity, you do not register from scratch again: you report a change of activities and premises.
The 036 receipt should show, at the very least, the effective date, activity, heading, place, schemes and periodic obligations. Do not file only the first page: keep the full copy submitted and its secure verification code.
Social Security: registering in the RETA beforehand
Registration in the Régimen Especial de Trabajadores Autónomos (RETA) must be reported before the start and can be made up to sixty calendar days in advance. It requires the Social Security number and activity details consistent with those given to Hacienda.
The procedure asks, among other things, for the date, activity, address, expected profit, the base or bracket under the current system, the mutua, the cover and the bank account. The provisional contribution is adjusted later according to the income figures the tax administration reports.
The date deserves special checking. If Laura starts on 15 October and applies in time, she must review the effective date she requests and the rules on registering part-way through a month. Applying late can shift the effective date, require back contributions and trigger surcharges or penalties. The sequence is set out in which comes first, the tax office or Social Security.
Laura's registration, step by step
Laura will provide graphic design to Spanish businesses from a room in her home and plans to start on 15 October.
- She confirms her DNI, Social Security number, IBAN and means of online access.
- She defines the service and checks how to choose the IAE heading.
- She works out the VAT and income tax treatment of her invoices and whether the professional activity carries withholding.
- She identifies the floor area of the home genuinely used for work and gathers her title to use it.
- She files the 036 before any transaction that marks the start for tax purposes.
- She registers in the RETA before 15 October, with expected profit and a mutua.
- She downloads both receipts and checks that date and activity match.
If before registering she buys a computer for 1,500 € plus VAT to work with, she should not wait for her first sales invoice to think about the tax office. An acquisition intended for the activity can mark the start for register purposes and requires keeping the invoice, the payment and evidence that it is used for the business. Expenses before the start have their own requirements, and they are not fixed by back-dating or forward-dating the registration artificially.
Additional details you may need
The list grows if you work with the European Union, sell to private customers in other countries, have premises, hire employees, pay rent subject to withholding or carry on several activities. You may need to apply for the ROI (the register of intra-Community operators), report obligations for Modelos 111 or 115, identify premises or separate VAT sectors.
If you register through a Punto de Atención al Emprendedor (a business start-up service point) and the Documento Único Electrónico (the single electronic form), still check the result in each administration. A joint process does not spare you from checking which details and obligations were finally recorded.
Nor do you need to wait for a signed client if you are already making purchases or preparations that count as the start for register purposes. Conversely, an idea, a reserved domain name or a sales conversation with no transactions does not always require you to set an artificial date. The facts are documented and a defensible date is chosen.
Checking the receipts
Before issuing your first invoice, compare this list:
| Check | Expected result |
|---|---|
| Identification | Correct tax number and Social Security number |
| Date | The same real start in both systems |
| Activity | Consistent description and classification |
| VAT and income tax | Schemes that suit the transactions |
| Withholdings | Registered only when you will pay or receive income subject to them |
| Bank account | Holder and IBAN verified |
| Addresses | Tax address, place of activity and address for notifications up to date |
A filing receipt does not guarantee that the boxes are right. If you find an error, file the change within the applicable deadline and keep the sequence. Do not open a second registration to correct the first.
At Salama Tax we review how the registration fits for tax purposes and whether the documents are consistent before you start. The decision on the RETA and on immigration permits must rest on each person's facts and documents; it is not presumed just because a first client exists.