The TA.0521 form is the Social Security document you need to register as self-employed in Spain. If you don’t submit it, you’re not enrolled in RETA, which means you can’t legally work as a freelancer, even if you’ve already registered with the Tax Agency. This is a very common mistake when you’re just getting started: many new autónomos assume that filing Form 036 or 037 is enough… but it isn’t. That’s why this article walks you through, in a clear and friendly way, what the TA.0521 is, when you need to file it, where to submit it, and how to fill it out properly, so you can avoid unpleasant surprises like penalties, back payments, or even losing reduced Social Security fees (such as the flat-rate scheme).
What the Modelo TA.0521 is
The Modelo TA.0521 is the official Social Security form used to register, deregister, or change data in RETA, the Special Regime for Self-Employed Workers. If you are starting as a freelancer, this form is used for your initial registration (alta).
This form links your activity to Social Security. It defines how much you pay every month, what you are covered for if you get sick or have an accident, and whether you qualify for future benefits. If the TA.0521 is missing or incorrect, Social Security treats you as not registered.
When the TA.0521 must be submitted
You must submit the TA.0521 before you start working, or up to 60 days before the start date you declare to the Tax Agency.
The start date on the TA.0521 must be the same as, or later than, the date declared in Modelo 036 or 037. If you file late, the consequences are clear. You can lose the reduced autónomo fee, and Social Security may charge missed contributions with surcharges.
Where and how to submit the TA.0521
The normal way to submit the TA.0521 is online through Import@ss, the Social Security portal. This is the fastest and most common option.
You can identify yourself with a digital certificate, Cl@ve, or SMS verification. Filing in person at a Social Security office is still possible, but appointments are scarce and delays are common.
Requirements before filling in the form
Before completing the TA.0521, you must already be registered with the Tax Agency using Modelo 036 or 037. Social Security checks this automatically.
You also need a Social Security number (NAF). If you do not have one, you must request it first.
A bank account in your own name is mandatory. Social Security fees are charged by direct debit, and third-party accounts are not accepted.
How to fill in the Modelo TA.0521 step by step
The form starts with your personal details. Enter your full name, ID or NIE, Social Security number, address, phone number, and email. These details must match your Tax Agency registration to avoid checks.
Next, select the type of procedure. New freelancers must choose registration (alta) and enter the activity start date. This date is critical and must align with the Tax Agency start date.
Then you define your professional activity. You include your business name if you use one, a clear description of what you do, your IAE code, your CNAE code, and the address where the activity takes place.
After that comes the contribution section. You choose your contribution base based on expected income brackets and select a collaborating mutual insurance provider. This directly affects your monthly fee and your coverage.
You then enter your bank details, including the IBAN, confirming that you are the account holder from which Social Security will collect the monthly fee.
Finally, you choose the notification address. This decides where official Social Security notices are sent. Mistakes here often lead to missed deadlines and penalties.
Choosing contribution base and mutual insurance
The contribution base sets how much you pay each month and the level of benefits you receive later. Higher bases mean higher fees but better coverage.
Under the current system, brackets are based on estimated income. You can adjust these estimates later if your income changes.
The mutual insurance provider covers sick leave, work accidents, and cessation of activity. If you do not choose one, Social Security assigns one automatically.
Common mistakes when filling in TA.0521
A frequent error is using a start date that does not match the Tax Agency registration. This often leads to reviews and loss of benefits.
Wrong or missing IAE codes are another common issue and can cause problems during inspections.
Many registrations fail because bank details are missing or the account is not owned by the applicant.
Another mistake is not choosing a contribution base or mutual insurance provider, which leads to automatic assignments that are often not ideal.
Variants of the TA.0521 form
There are different versions of the TA.0521 depending on the type of self-employed worker.
These include standard freelancers, family collaborators, company directors (autónomos societarios), and TRADE workers. The structure is similar, but some sections change depending on your situation.
Relationship between TA.0521 and reduced self-employed fees
To access reduced Social Security fees, the TA.0521 must be submitted correctly and on time. Late filing or errors can mean losing the reduced rate completely, even if you meet all other conditions. This is one of the most expensive mistakes new freelancers make in Spain.
Bottom line
The Modelo TA.0521 is mandatory to work legally as a freelancer in Spain. It must be coordinated with your Tax Agency registration and completed accurately. Doing it right from the start avoids penalties, delays, and the loss of reduced Social Security fees.
