# What is modelo TA.0521? > TA.0521 is not on Social Security's current worker-forms list. The self-employed alta is the Import@ss service Alta en trabajo autónomo. - Page: https://autonomo.eus/blog/what-is-modelo-ta0521 - Last checked: 22 October 2026 Short answer. The steps are on the guide. People still search for modelo TA.0521 as a Social Security form. **It is not on the current list of worker forms, and the self-employed alta that Import@ss offers today is the service Alta en trabajo autónomo.** This page does not describe TA.0521 as a paper form, because the pages opened for this answer do not say that. ## What it is The [list of worker forms](https://www.seg-social.es/wps/portal/wss/internet/Trabajadores/Afiliacion/10817/31190), opened on 22 October 2026, includes Form TA1 for affiliation, a Social Security number or a change of data, and a long set of other TA forms for employed workers, seafarers, special agreements and other schemes. A search of that page does not find TA.0521 or TA0521. What TA.1 is, and why it is a different form, is [What is modelo TA.1?](https://autonomo.eus/blog/what-is-modelo-ta1). The service Import@ss offers for starting self-employed work is [Alta en trabajo autónomo](https://portal.seg-social.gob.es/wps/portal/importass/importass/Categorias/altas%2C+bajas+y+modificaciones/altas+y+afiliacion+de+trabajadores/alta_trabajo_autonomo). The page says: if you want to work on your own account, check the requirements and register before you start the activity. The button is "Solicitar alta". It says you must ask for the alta before you start, and that you can file it up to 60 days before. If you have already started, you still report it, and it is treated as out of time for every purpose. It says registering means a monthly fee. It asks, during the procedure, for the IAE code and the tax administration you belong to, the CNAE code except for religious workers, the start date and the address of the activity, an estimate of annual net income, a contribution base and any benefits that apply, a collaborating mutua, and a bank account for the fee. The page also says it may ask for other details. Those are the items it names. This answer does not turn them into steps. The [practical guide](https://portal.seg-social.gob.es/wps/portal/importass/importass/Colectivos/trabajo+autonomo/guia) points at the same service, "Alta en trabajo autónomo", and says you also register for IAE with the Agencia Tributaria or the Hacienda Foral. It says the Social Security alta must match the Hacienda alta and must be on or before the start date, or you lose benefits on the fee and a surcharge may apply. It says you need your NUSS or NAF. It says registering as autónomo is obligatory. The [magazine's alta guide](https://revista.seg-social.es/-/guia-para-darte-de-alta-en-la-seguridad-social-como-trabajador-autonomo) says the IAE registration is done first, with the tax agency or the foral agencies, depending on where you live, and that in Import@ss you identify with Cl@ve, a digital certificate, or any valid method, then open the alta service and press "Solicitar alta". Two official texts say the procedures are electronic, without using the name TA.0521. The [Social Security page on affiliation in the self-employed scheme](https://www.seg-social.es/wps/portal/wss/internet/InformacionUtil/44539/44113/44128) says that from 1 October 2018 it is compulsory for self-employed workers to carry out their procedures with Social Security online, through the electronic office or through an authorised person in the RED system. [Orden ESS/214/2018](https://www.boe.es/buscar/act.php?id=BOE-A-2018-3080), in the BOE, extends the RED electronic data system to self-employed workers in the special scheme for self-employed workers and in the scheme for sea workers, with the exceptions the order itself states. Its preamble says the first transitional provision gives those workers six months to join RED. The order says it enters into force on the first day of the month after it is published in the BOE. That page dates the initial text 6 March 2018, so the date is 1 April 2018. This answer does not invent a sentence that joins that period to the name TA.0521. The order does not use that name. Import@ss, the portal where that alta now sits, is [What is Import@ss?](https://autonomo.eus/blog/what-is-importass). ## What is different in Euskadi The electronic obligation and the Import@ss alta are state Social Security rules. They read the same way in Álava, Bizkaia and Gipuzkoa. The practical guide and the magazine both say the IAE registration depends on where you live: the state tax agency or the foral agency. Those pages do not say which one applies in Álava, Bizkaia or Gipuzkoa. This page does not tell you to file a Basque tax model with the state agency. It only repeats what those Social Security pages say about which body they name. Which office applies here is [Your Hacienda Foral](https://autonomo.eus/steps/hacienda-foral). ## Where to read the steps The alta, in Import@ss, is [Register with Social Security](https://autonomo.eus/steps/register-social-security). The number that service asks for, and modelo TA.1, are [Get your Social Security number](https://autonomo.eus/steps/social-security-number). ## Official sources - [Social Security: worker forms](https://www.seg-social.es/wps/portal/wss/internet/Trabajadores/Afiliacion/10817/31190) - [Import@ss: alta in self-employed work](https://portal.seg-social.gob.es/wps/portal/importass/importass/Categorias/altas%2C+bajas+y+modificaciones/altas+y+afiliacion+de+trabajadores/alta_trabajo_autonomo) - [Import@ss: practical guide for self-employed work](https://portal.seg-social.gob.es/wps/portal/importass/importass/Colectivos/trabajo+autonomo/guia) - [Social Security magazine: registering as a self-employed worker](https://revista.seg-social.es/-/guia-para-darte-de-alta-en-la-seguridad-social-como-trabajador-autonomo) - [Social Security: affiliation in the self-employed scheme](https://www.seg-social.es/wps/portal/wss/internet/InformacionUtil/44539/44113/44128) - [BOE: Orden ESS/214/2018](https://www.boe.es/buscar/act.php?id=BOE-A-2018-3080) --- Free, independent information. Not an official government website or a gestoría. General information, not legal, immigration or tax advice. Confirm current requirements with the authority before you act. Report a mistake: a@halawa.io. Source: Autónomo.eus (https://autonomo.eus).