The A1 certificate proves that a posted worker or self-employed person stays covered by their home country's social security while working in Portugal.
What it is
The A1 certificate is a form used across the European Union and the European Economic Area (EEA, the EU plus Iceland, Liechtenstein and Norway). It confirms which country's social security system covers a worker or a self-employed person while they work temporarily in another EEA country, such as Portugal, instead of both countries claiming coverage at once.
What it is for
Without the A1, a person working temporarily in Portugal could end up owing social security contributions in two countries at once, or facing confusion about which country actually covers them if an accident happens. The certificate settles this in advance and avoids double payment, giving both the worker and the client clarity from the start.
Who needs it?
A person posted to work in Portugal by an employer based in another EU or EEA country normally needs the A1 certificate. A self-employed person from another EU or EEA country, temporarily working in Portugal, also needs it to keep paying contributions at home instead of in Portugal.
Where to get it and how long it is valid
The certificate is issued by the social security authority of the person's home country, before the work in Portugal starts. It is valid for the period stated on the certificate, which usually matches the expected length of the posting or the self-employed activity, and can sometimes be extended if the work continues.
What to watch out for
Sometimes no A1 certificate is available, or the one available does not fit the situation. The absence of an A1 does not by itself decide which country's social security legislation applies or where contributions are due. That follows from the applicable coordination rules (for EU and EEA cases, Regulation (EC) No 883/2004) or, for countries outside the EU and the EEA, from a bilateral social security agreement, where one exists. A Certificate of Coverage issued under such an agreement can serve the same purpose as an A1. If it is unclear which rules apply, ask the social security institution of the home country and the Portuguese Segurança Social.
Having no A1 does not automatically mean that Portuguese social security applies, and having one does not answer every question. Check which rules, or which agreement, cover the situation.