How this works
A NISS has 11 digits and ends in a check digit. That digit comes from the first 10: multiply each by the weights 29, 23, 19, 17, 13, 11, 7, 5, 3 and 2, add the products, take the remainder of dividing by 10, then compute 9 minus that remainder. The first digit gives the holder type: 1 for an individual, 2 for a legal entity. If the result does not match the 11th digit, the number is wrong.
Frequently asked
How is the NISS check digit calculated?
The first 10 digits are each multiplied by the weights 29, 23, 19, 17, 13, 11, 7, 5, 3 and 2. The 10 products are summed, you take the remainder of dividing by 10, then compute 9 minus that remainder. The result must equal the 11th digit. If it does not match, the number is mistyped.
Does this tell me who a NISS belongs to?
No. The check is purely mathematical and runs in your browser — we do not query Segurança Social or any database. It only confirms the number is well-formed and shows the holder type from the first digit.
What does the first digit mean?
A NISS starts with 1 when the holder is an individual (a citizen) and with 2 when it is a legal entity (a company, association or other body). Any other value in the first digit makes the number invalid from the start.
Is a formula-valid NISS a real one?
Not necessarily. Passing the formula only guarantees the number is well-built. It may exist, belong to someone else, or never have been issued. To confirm a real NISS, use Segurança Social Direta or a Segurança Social desk.
How do I get a NISS if I do not have one?
You can request it online via Segurança Social Direta (the NISS request section) or in person at a Segurança Social service desk. Foreigners can request their identification numbers through the gov.pt portal.
DISCLAIMER
This tool only checks the number’s mathematics and identifies the type from the first digit. It does not confirm whether a NISS exists, is active or who it belongs to, and is no substitute for an official check with Segurança Social. Not advice.