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).
The RFC (federal taxpayer ID) is the key to your entire tax life — and getting it right the first time saves you the two classics: the wasted trip back to the office over one piece of paper, and the "half-done" registration (an RFC with no e.firma or Contraseña) that's useless for anything practical. Here's the complete route by case, with what to bring and what you need to walk out holding.
Route 1 — Online with your CURP (the simple start)
Any individual over 18 can register online with their CURP (national population ID) through the SAT portal (the "Get your RFC with CURP" procedure) — enter your data, address, and you get your RFC with its acknowledgment in minutes, without setting foot in an office. The nuance that matters: online registration signs you up in general terms "with no tax obligations" (the registration banks and employers ask for) — if you're going to invoice, open a business or get paid on your own account, you also need to register under a regime with economic activities, and that step (together with the e.firma) is the one that normally takes you to the office. For an employee, the employer can also register you. Our recommendation is not to stop at Route 1: an RFC without an e.firma is an account with no keys.
Route 2 — At the office by appointment (the complete one)
Book the registration procedure on the SAT appointment portal (citas.sat.gob.mx) and — on the same trip — the e.firma (the SAT's digital signature) one. The standard documents: CURP, a valid official ID, a recent proof of address (in your name; the rules accept several types — a bank statement is usually the cleanest), email and phone, and a USB drive for your e.firma files. That day you define your tax regime according to what you'll do — the decision most people make lightly and that fixes how much ISR you'll pay (run it in our comparator before you go: salaries, RESICO, professional activity, rental). Legal entities: registration goes hand in hand with the notary who incorporates the company (or online with the representative's power of attorney), with the legal representative's e.firma as an operational prerequisite.
The exit checklist: don't leave without this
You should walk out of the procedure with four things: (1) your RFC with its ID card/registration acknowledgment; (2) your active e.firma — the .cer and .key files with their password, backed up in two places (it's your digital legal identity: it signs returns, procedures, contracts; losing it means an in-person renewal); (3) your portal Contraseña (password, formerly the CIEC) — your day-to-day access; and (4) your tax status certificate (constancia de situación fiscal) — the document everyone will ask you for (banks, employers, clients who need to invoice you with CFDI 4.0). And the two immediate steps for the newly registered with activity: enable your Tax Mailbox (Buzón Tributario — mandatory, with fines for not doing it, and where the SAT notifies you of everything) and — if you're going to invoice — generate your Digital Seal Certificate. From there, your obligation to file runs even if you have no income — the most heavily fined rookie mistake in the system.
Are you about to start an activity — yours or a family member's just starting out?
Registration is a procedure; choosing the regime and the initial architecture (which activity, which regime, what gets invoiced and how) is strategy — and it's much cheaper done right on day one than corrected in year two. In one session we set up the complete start: the optimal regime with numbers, a calendar of obligations, and the invoicing setup.
Frequently asked questions
Does getting an RFC force me to pay taxes right away?
Registering doesn't generate taxes by itself — the obligations depend on the regime and activities you declare. 'No obligations' files no returns; with economic activity, you file from the first period even if it's a zero return. That's why the regime is chosen with intent, not with whatever option the office line suggested.
Can I get an RFC for my underage child?
Yes — minors can register (with their parents/representatives present for the procedure) and it's useful for investments in their name or payroll for those over 16 in certain cases. Registering minors has its own documentary requirements (birth certificate, parents' IDs). For family wealth structures, it's a piece that activates when the design calls for it.
I'm a foreigner residing in Mexico, is it the same procedure?
Registering foreigners also requires your valid immigration document (temporary/permanent residency) and has its own in-person procedure sheet. With activity in Mexico you're a full taxpayer — and your cross-border situation (treaties, tax residency) deserves separate analysis before choosing a regime.
Does the tax status certificate expire?
It has no formal validity period, but everyone asks for it 'recent' (weeks, not years) because it reflects your status as of the issue date. You can download it from the portal with your RFC and Contraseña, free and as many times as you need — save the PDF, but regenerate it when asked: it's faster than arguing about its date.
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 — a reply the same business day.