You’re filling in a form, registering with Social Security or a client asks for your NISS - and you realise you have no idea what your Social Security number is.
It feels like one of those numbers everyone memorised except you. But in fact it’s closer to hand than you think, and in three minutes you’ll have it.
First: the NISS is not the NIF
This is a very common mix-up. They’re two different numbers, from two different bodies:
- The NIF (tax identification number) has 9 digits and is your number at the tax office (Finanças). It’s what you use to invoice and for IRS.
- The NISS (Social Security identification number) has 11 digits and is your number at Social Security. It’s what you use for contributions, declarations and benefits.
Swapping one for the other on a form just slows your request down. Always check which is which.
Where your NISS is
There are three places to find it.
- On the back of the Citizen Card. When you request the Citizen Card for the first time, the NISS is assigned to you automatically and printed on the back of the card. It’s the most immediate spot - just turn it over.
- In Segurança Social Direta. Log in at app.seg-social.pt with the Chave Móvel Digital or the Citizen Card, click the profile icon, choose “Perfil” and then “Dados pessoais”. The NISS appears there, with the rest of your identification. (See the Segurança Social Direta guide; if you can’t get in, unlock your access. Step by step with screenshots in the Help Center.)
- Through the Social Security phone line. If you have the old lifelong identity card and never learned your NISS, call the Linha Segurança Social (210 545 400 or 300 502 502), on working days from 9am to 6pm, or go to a service desk.
Inês’s case
Inês, a photographer in Aveiro, went to register for Segurança Social Direta and needed her NISS. She had no idea what hers was.
She turned over her Citizen Card, found the number on the back and carried on without leaving her chair. The number had been in her wallet the whole time.
And if you don’t have a NISS yet
Not everyone has a NISS assigned - for instance, someone who arrived in Portugal recently or has the lifelong identity card.
The request is free and is made online on the Social Security portal, by the person themselves. You can also handle it in person at a service desk, with an appointment booked through the SIGA platform or the SigaApp. The right order is: first the NIF, then you open your activity at the tax office (which only needs the NIF), and then you enrol with Social Security - that’s when the NISS is assigned to you. So you don’t need the NISS before opening your activity.
Careful: having a NISS is not the same as being enrolled as a self-employed worker with Social Security. The NISS is just your identification number; enrolling as a self-employed worker is a separate step, which happens when you open your activity at the tax office and Social Security frames you. Having the number doesn’t enrol you on its own.
Where FIZ comes in
Your NISS is the key that links everything Social Security. Once you have it, FIZ handles the tedious part: it calculates and files your quarterly Social Security declaration from the receipts you issue, without you having to memorise numbers or deadlines.
In summary
- The NISS (11 digits, Social Security) is not the NIF (9 digits, tax office). Don’t swap them on forms.
- You’ll find the NISS on the back of the Citizen Card, in Segurança Social Direta (Perfil - Dados pessoais) or through the Social Security phone line.
- If you don’t have a NISS yet, the request is free. The order is: NIF → open your activity at the tax office (which only needs the NIF) → enrol with Social Security, which assigns you the NISS.
