Miguel will start working on his own account on 8 November. He first registers with Social Security from that date and leaves Modelo 036, the Spanish tax registration return, until he issues his first invoice. That approach is wrong: Hacienda, as the Spanish tax office is commonly known, treats the activity as started from the moment he carries out transactions, purchases, collections, payments or hiring aimed at the business. Both procedures must be completed beforehand and share a consistent date; in practice the tax set-up is prepared first and coordinated immediately with the RETA, the Social Security scheme for the self-employed.
Two separate registrations
Modelo 036 puts you on the Censo de Empresarios, Profesionales y Retenedores (the register of businesses, professionals and withholding agents) and reports your activities, premises, VAT, income tax (IRPF), withholding and special registers. Registration in the RETA starts your enrolment and your contributions with the General Treasury of Social Security.
| Administration | Procedure | What it determines |
|---|---|---|
| Agencia Tributaria (tax agency) | Modelo 036 | Activity and tax obligations |
| Social Security | RETA registration | Contributions, cover and effective date |
Filing one does not automatically replace the other. The Documento Único Electrónico (the single electronic form) can pass data to several administrations where it applies, but you must check the outcome and the receipts issued by each of them.
Since 3 February 2025 Modelo 037 no longer exists. Registration for tax purposes is made on the 036, including the simplified assistance available for certain cases involving individuals.
The tax date can start before the first sale
The registration return is filed before starting activities, carrying out transactions or the obligation to withhold arising. The Agencia Tributaria considers that an activity has started when goods or services are supplied or acquired, collections or payments are made, or staff are hired for a business or professional purpose.
If Miguel buys a computer for his activity on 2 November and starts providing services on the 8th, waiting until his invoice of 30 November may leave a relevant preparatory transaction outside the registration. He must work out which date reflects the facts and keep the invoice and evidence of what the purchase is used for.
Not every abstract preparation counts as starting. Thinking of a name, opening a folder or researching the market does not carry the same weight as buying equipment, renting an office or receiving an advance payment. The date rests on objective acts; it is not brought forward or pushed back just to gain an advantage.
You can describe the timeline, the first purchase and the first engagement in the self-employed registration form. With those details a defensible sequence is set before anything is filed.
The RETA registration can be made up to sixty days in advance
Registration with Social Security must also be made before the start, and it can be requested up to sixty calendar days beforehand. That lets you prepare both registrations without waiting until the day before. Giving a future date does not mean you start contributing on the day you apply: the effects are tied to the date you report, under the applicable rules.
The procedure requires your Social Security number, the activity, your address, an estimate of your income, a mutua (a private mutual association that manages certain benefits alongside the public system), the cover you choose and a bank account. The provisional contribution is not decided by looking only at turnover; the system based on real income starts from the computable net profit and provides for a later adjustment.
If you do not yet have your identification or the basic details, review what you need to register before setting the date.
A working order that avoids contradictions
The prudent sequence is this:
- Define the activity, the heading, the transactions, the place and the real date.
- Prepare the 036 and check the obligations that will follow from it.
- File the tax registration before the start.
- Register in the RETA, also before the start, within the sixty-day window.
- Check the receipts, dates and descriptions.
- Issue invoices and record expenses in line with the set-up you declared.
Saying that "the tax office comes first" does not mean leaving weeks between the two procedures, or starting work in that gap. It means the tax classification must be settled so that the RETA records a consistent activity and date. Both can be filed in a coordinated way before the same starting day.
An example with a calendar
Miguel signs the contract with his first client on 20 October. The service starts on 8 November. He needs to buy a professional software licence on 1 November.
| Date | Action |
|---|---|
| 20 October | Reviews the contract, the activity and the heading |
| Before 1 November | Files the 036 if the purchase marks the start for tax register purposes |
| Before 8 November | Registers in the RETA with the real applicable date |
| 1 November | Keeps the invoice and proof of payment for the licence |
| 8 November | Starts providing the service |
| When invoicing | Applies VAT and withholding according to the registration |
The contract on its own needs to be examined: it may be a commitment for the future, or it may already give rise to an advance, an obligation or a service. The example does not always make 1 November the right date; it shows why the facts before the first visible piece of work are reviewed.
What happens if you reverse the order
Registering in the RETA first does not automatically invalidate the registration if the 036 is completed before any transactions take place and both dates are consistent. The risk appears when Social Security shows an activity that has started while the tax office still has no registration, or when invoices, purchases or collections already exist.
The authorities can cross-check dates. A bank fee, a contract, an invoice received or the registration of an employee can show that the activity started earlier. Putting it right afterwards means assessing a change to the tax register, the late registration and the returns that were omitted; it is not fixed by choosing a different date with each administration.
Nor is it wise to file a premature 036 and forget the RETA for months. While you remain on the tax register, Hacienda expects the corresponding periodic returns, even if they show nothing due. And Social Security can claim enrolment and contributions from the proven start date.
Late registration
If you have already started, first gather evidence of the date: contracts, invoices issued and received, bank statements, delivery emails, advertising showing real availability and the registration of any employees. Then put the two regularisations and the outstanding tax returns in order.
A late RETA registration can have retroactive effects and lead to back contributions, surcharges and penalty proceedings. With the tax office, returns filed late may attract the surcharges provided for if they are filed voluntarily before any formal request, while missing register or information returns have their own treatment. That specific question is covered in I registered late: what can happen.
Do not invent a recent date to reduce contributions if there is evidence of earlier activity. Nor should you backdate everything to your first conversation with a client when there is no need to. The regularisation must identify the first event that legally marks the start in each area and explain any real difference.
Check the obligations after filing
Download the full copy of the 036 and the RETA receipt. Check:
- name, tax number and Social Security number;
- start date and effective date;
- activity and IAE heading (the activity classification of the Spanish business activity tax);
- tax address, premises and place of work;
- VAT, income tax and withholding;
- expected income, mutua and bank account;
- the returns that result and how often they are due.
If the 036 registers you for Modelo 115 because of rented premises, you will have to withhold tax from the landlord where it applies. If it registers you for intra-Community transactions, the ROI (the register of intra-Community operators) must not be taken as granted just because you applied for it. Every box opens obligations that continue until they are changed or cancelled.
Changing the date because the project is delayed
If you filed in advance and the start is postponed, do not leave the registrations unreviewed. Before the original date, make the changes or cancellations each procedure allows and keep a record of the reason. Starting a month later while keeping obligations from the earlier date can generate unnecessary contributions and returns.
If the project is cancelled after preparatory purchases have been made, it is not always correct to say there was never any activity. For VAT purposes, proven preparatory acts may be relevant even if no sales ever take place. A genuine cancellation has to be distinguished from a badly chosen date.
At Salama Tax we coordinate the tax set-up of your registration with the details needed for Social Security, without filing dates that contradict each other. The aim is for the contract, the purchases, the 036, the RETA and the first invoice to tell the same story.