How to Register as an Autónomo in Spain: Modelo 037, IAE, CNAE, Social Security and Baja

Registering as self-employed in Spain is not just one form. To start correctly, an autónomo usually needs to register with the Spanish Tax Agency, choose the right economic activity, and complete the Social Security registration as well.

If you're wondering how to become self-employed in Spain, the process usually involves two separate registrations: one with Hacienda and one with Social Security.

This guide explains the main steps: filing an Alta with Hacienda, choosing an IAE code, registering with Seguridad Social, selecting a CNAE code, and understanding what happens when you later file a Baja.

Before registering as an autónomo, most foreigners will already have obtained a NIE number. New arrivals to Spain are often confused by the difference between a NIE and a TIE residence card. If you are not sure which document you have or need, see our guide on NIE vs TIE in Spain: What's the Difference?.

Step 1: Register with Hacienda

The first step is to register your activity with the Spanish Tax Agency, known as Agencia Tributaria or Hacienda.

To complete this registration, you will normally need a NIE number. The NIE is your foreigner identification number used by Hacienda, banks, Social Security and other Spanish authorities. It should not be confused with a TIE residence card. Learn more in our guide on NIE vs TIE in Spain.

For many individual freelancers, this is done through Modelo 037, the simplified census declaration. In other cases, Modelo 036 may be required. Both forms are used to communicate an Alta, modification or Baja in the Census of Entrepreneurs, Professionals and Withholders.

The official AEAT electronic office can be accessed here:

Agencia Tributaria Electronic Office

The official census procedure page is available here:

Modelo 036 / 037 census procedure

Can You Register as an Autónomo Online?

In many cases, yes. The Hacienda part of the registration can usually be completed online through the AEAT electronic office, and the Social Security registration can be completed through Importass.

To do this yourself, you normally need a digital certificate, Cl@ve access or another accepted electronic identification method. Without online access, many people use a gestoría or request help from an authorized professional.

Example of Modelo 037, the simplified census declaration used by many autónomos to register their activity with Hacienda.

What information is included in Modelo 037?

Modelo 037 includes the basic information Hacienda needs to identify the taxpayer and understand the economic activity.

• Personal identification details
• Tax address
• Contact details
• Start date of the activity
• Economic activity
• IAE heading
• VAT obligations
• Personal income tax obligations

How Long Does It Take to Register as an Autónomo?

The actual online registration can often be completed quickly if you already have the required identification and documents.

• Hacienda registration may be completed the same day
• Social Security registration may also be completed the same day
• Getting a digital certificate or Cl@ve access can take longer
• Choosing the correct IAE and CNAE codes may require extra review

In simple cases, the whole process can be completed in one day. In more complex cases, especially for foreigners, visa applicants or activities with special VAT treatment, it may take longer.

The Alta date is important because it should match the real start of the professional or business activity. It may also affect tax filing obligations and Social Security registration.

Many people assume that filing Modelo 036 or Modelo 037 is simply a preparatory step that can be completed long before they actually start working. In reality, an early registration may create tax filing obligations even if the activity has not truly begun. We discuss a real case involving visa applicants, retroactive obligations and Hacienda penalties in our guide on the hidden risk of registering with Hacienda before work authorization is approved.

Step 2: Choose the correct IAE code

One of the most important parts of the Hacienda registration is the IAE code. IAE stands for Impuesto sobre Actividades Económicas.

In practice, the IAE code tells Hacienda what type of activity you perform. Even when an autónomo does not actually pay IAE due to the applicable exemptions, choosing the correct heading still matters.

A wrong or too generic IAE code can create problems later, especially when issuing invoices, applying for certain registrations, explaining expenses, or modifying the activity.

Examples of activities that need careful classification

• Software development
• Online consulting
• Marketing and advertising services
• Engineering services
• Import and export activity
• Teaching or training services
• Design, content creation or digital services

Some activities fit clearly into one category. Others may require a more careful review, especially when the business combines several services.

Step 3: Register with Social Security

Registering with Hacienda is not enough. An autónomo must also register with Seguridad Social under the special self-employed workers regime, commonly known as RETA.

This is done through Importass, the official portal of the Spanish Social Security Treasury.

Importass - Social Security portal

The official page for registering as self-employed is available here:

Alta en trabajo autónomo

During the Social Security registration, you may need to provide information such as the start date, your activity, expected income, contribution details and your CNAE code.

Registering with RETA does not mean you cannot keep or later obtain a traditional employment contract. Spain allows many professionals to be both employees and autónomos at the same time, a situation known as pluriactividad.

If you are wondering whether a full-time job affects RETA contributions, Modelo 130, Modelo 303, pension rights or Social Security obligations, see our guide on being an autónomo and a full-time employee in Spain at the same time.

Shortly after registering as an autónomo, many freelancers are surprised when their bank starts offering products such as life insurance, health insurance or professional liability insurance. These products are not always mandatory. Learn more in our guide on why Spanish banks try to sell insurance to autónomos, expats and digital nomads.

IAE and CNAE are not the same

A common mistake is assuming that IAE and CNAE are the same thing. They are not.

The CNAE code may be different from the IAE code even when both describe the same business. For example, a consultant, software developer or online service provider may need one classification for Hacienda and another classification for Social Security.

The important point is that both codes should accurately reflect the real activity being carried out.

Common mistakes when filing Alta

• Filing Alta with Hacienda but forgetting Social Security
• Choosing an IAE code that is too broad
• Using a CNAE code that does not match the real activity
• Starting to invoice before the registration is complete
• Not checking whether quarterly tax returns will be required
• Using a personal address without considering tax implications
• Registering with Hacienda months before the activity actually starts

Do You Need to Register in These Situations?

If you are unsure whether occasional income requires registration, see our guide on whether you can invoice without being autónomo in Spain.

These mistakes are usually fixable, but correcting them later may take time and may create unnecessary administrative work.

Step 4: Understand your ongoing obligations

After the Alta is completed, the autónomo may need to file regular tax returns depending on the activity and tax setup.

Common obligations may include quarterly VAT returns, personal income tax prepayments, annual summaries and maintaining invoice records.

The next question most new autónomos ask is how much tax and Social Security they will actually pay. Before starting your activity, it is worth estimating your expected income, expenses, RETA contribution and quarterly tax position.

You can use our autónomo tax calculator for Spain to get a practical estimate before filing or invoicing.

If you need help understanding quarterly VAT reporting, see our guide on how to file Modelo 303 yourself in Spain.

For income tax prepayments, you may also want to read our guide on how to file Modelo 130 yourself in Spain.

This is why the initial registration matters. The choices made in Modelo 037 or Modelo 036 can determine which forms Hacienda expects from you later.

How to file Baja as an autónomo

If you stop your self-employed activity, you should not simply stop invoicing. You usually need to file a Baja with both Hacienda and Social Security.

Baja with Hacienda

Hacienda explains that a taxpayer should file a census Baja when they cease all business or professional activity, or when they no longer need to be included in the Census of Entrepreneurs, Professionals and Withholders.

Official AEAT page:

When to file Baja in the census

Baja with Social Security

Social Security also has a separate procedure for deregistering from self-employed work.

Official Importass page:

Baja en trabajo autónomo

If you file Baja only with one authority, you may still have pending obligations with the other one. This is one of the most common mistakes when closing an activity.

What happens to the reduced autónomo fee?

Many new autónomos can benefit from a reduced Social Security contribution, commonly known as Tarifa Plana.

Before filing Baja, it is important to understand the consequences. According to Social Security guidance, an autónomo may benefit from the reduced rate if they have not been included in the special self-employed regime during the previous two years, or during the previous three years if they had already benefited from the reduced rate before.

In practical terms, if you used the reduced contribution, closed your activity, and then decide to register again too soon, you may lose access to the reduced monthly contribution and have to pay the normal amount.

Many freelancers are surprised to learn that Tarifa Plana is usually a real reduction rather than a payment that must automatically be repaid later. If you are unsure how the reduced contribution works or how it differs from Social Security regularization, see our guide on whether the Tarifa Plana really saves money.

This is why Baja should not be treated as a casual pause unless you are sure that closing the activity is the right decision.

Alta vs Baja checklist

Related guides

• How Much Tax Will I Pay as an Autónomo in Spain?
• How to File Modelo 303 Yourself in Spain
• Can You Invoice Without Being Autónomo in Spain?
• Why Spanish Banks Freeze Accounts: What Foreigners and Autónomos Need to Know
• Why Is My Spanish Bank Trying to Sell Me Insurance?
• Can You Invoice Without Being Autónomo in Spain?
• How to File Modelo 130 Yourself in Spain
• Do Autónomos Have Consumer Rights in Spain?
• How to Switch from a Non-Lucrative Visa to Autónomo in Spain (Real Case Study)
• Hacienda Requested Documents for a VAT Return (Modelo 303)
• DAC7 reporting and Upwork income

Final thoughts

Registering as an autónomo in Spain is manageable, but it should be done carefully. The most important point is that Hacienda and Social Security are two separate registrations.

A correct Alta should include the right tax activity, the right IAE code, a matching Social Security registration and an appropriate CNAE code.

The same applies when closing the activity. A proper Baja normally means closing the activity with both Hacienda and Social Security, while also understanding the effect on future benefits such as the reduced autónomo contribution.