My point of view:

  • EU nationality (Belgium)
  • not Portuguese citizen
  • Portuguese resident (3+months with CRUE)
  • not resident in another country
  • citizen of another country (Belgium)

SNS

You need this for for public health care in Portugal

A National Health Service (SNS) national user number is allocated to anyone who needs healthcare at SNS public facilities.

Non-nationals are allocated a number the first time they go to a public health facility such as a health centre or a hospital.

Being allocated a health user number is not a guarantee that your healthcare costs will be covered by the SNS.

Simply having a healthcare user number is not a guarantee that your healthcare costs will be covered by the SNS. For the SNS to cover your healthcare costs, the following information must also be associated with the registration of your healthcare user number: https://eportugal.gov.pt/en/servicos/pedir-o-numero-de-utente-do-sns

EHIC

You need this to get health insurance outside of Portugal in the EU “free” travel medical insurance within EU.

The European Health Insurance Card (EHIC) allows you to receive medical assistance during a temporary stay in a country of the European Union, Iceland, Liechtenstein, Norway or Switzerland.

Medical care is provided through that country’s social security system, which means that some health care may not be free of charge and may require the payment of user fees. https://eportugal.gov.pt/en/servicos/requerer-o-cartao-europeu-de-seguro-de-doenca-da-seguranca-social

NIF (aka TIN)

You need this pretty much for everything: long term renting, big purchases (car, house,…) , electricity,… You can request one while not living in Portugal, on a foreign address. The day you link your NIF to a Portuguese residence, is often the date you become tax resident.

NIF is primarily for taxation and business-related matters, including income reporting and business transactions. https://medium.com/@digital.inlis/nif-vs-niss-portugal-key-differences-explained-b4e0120967db

NISS

You need this to when you get a job.

NISS is focused on social security and access to social benefits, such as healthcare and unemployment support. https://medium.com/@digital.inlis/nif-vs-niss-portugal-key-differences-explained-b4e0120967db

CRUE

You need this when you live in Portugal for 3 months as EU nationality. EU nationals are allowed to live & work in any other EU country, but after 3 months they must inform the country. The CRUE is the document you get when you inform Portugal. (and is used as the main proof of residency)