Written for Mexico. This analysis applies to Mexican federal tax law — ISR (income tax), IVA (VAT) and SAT rules — and cites Mexican statutes. Amounts are in Mexican pesos (MXN).
They ask for it for the new job, for Infonavit (the national housing fund), for your Afore (retirement-savings) balance — and nobody remembers where it went. The good news: the Social Security Number is no longer a stand-in-line procedure: it's obtained or recovered online, free, in about five minutes, with two things you already have: your CURP (national ID code) and an email address. The direct links are in our Resource Center.
What exactly the NSS is
Eleven digits, unique and permanent: the IMSS (the social-security institute) assigns it to you once in your life and it doesn't change even if you switch employers, stop contributing for ten years, or work at twenty companies. It's the key to your entire social-security history: your contributed weeks, your Infonavit housing subaccount, your Afore and, at the end of the road, your pension. A surprising fact: you don't need to be working to have one — anyone with a CURP can request one, and it's worth doing before your first job (employers ask for it when they hire you).
The two routes, step by step
Online (the fast one): go to the IMSS NSS Assignment or Lookup service, enter your CURP and your email, confirm your details — and download your NSS card as a PDF on the spot. If you already had a number (even without knowing it), the system locates it; if you've never had one, it assigns it to you. The same procedure lives in the IMSS Digital app (iOS/Android), which also lets you look it up every time you lose it again. If you don't remember your CURP, you can look it up and print it in a minute on the RENAPO (national population registry) portal — also linked in the Resource Center.
In person (plan B): any IMSS Subdelegación (local office) with official ID, your CURP and a proof of address — only necessary when the system finds inconsistencies in your data (duplicate names, an erroneous CURP), which is exactly the case where it's worth fixing at the root, because that inconsistency will follow you into every future procedure.
Is the NSS for a bigger procedure — a pension, Infonavit, or your first hire as an employer?
The NSS is the door; what lies behind it (contributed weeks, pension modality, Infonavit pre-qualification, correct employer registrations) is where years of benefits are won or lost. If you're putting your social-security life in order — yours or your employees' — the full diagnostic takes one session.
Frequently asked questions
Are the NSS and my Afore number the same thing?
Your Afore account is identified precisely by your NSS (and your CURP) — there is no separate 'Afore number.' If you don't even know which Afore you're with, the e-SAR portal tells you using your NSS and CURP.
I've never worked formally — can I have an NSS?
Yes — assignment doesn't require an employment relationship. Request it online with your CURP; you'll have it ready for your first job, to enroll as a student in certain cases, or for the voluntary-enrollment scheme if you're self-employed.
My employer is asking for my NSS 'to register me' — is that normal?
Yes — the employer is required to register you with the IMSS and needs your NSS for the registration. What you should verify afterward: that the registration actually exists and shows your real salary — you can check it in a minute with your certificate of contributed weeks. Registration at a salary lower than your real one is among the most common employer frauds and hits your pension and your Infonavit loan directly.
Let's talk about your case
The first step is always the same: an honest diagnostic of where you stand. Write to us on WhatsApp or call us — a reply the same business day.