CURP and RFC: the two Mexican numbers every American resident ends up needing

The CURP identifies you to the Mexican government. The RFC identifies you to the tax office. Residents usually get the first one automatically and apply for the second.

The short version

• The CURP (Clave Única de Registro de Población) is an 18-character ID code for everyone who lives in Mexico, foreigners included [1]. It's the closest thing Mexico has to a Social Security number.
• The RFC (Registro Federal de Contribuyentes) is your taxpayer ID with the SAT, Mexico's IRS. Anyone 18 or older who needs to be registered can sign up [2].
• Foreigners register with a valid immigration document in place of a birth certificate, so you need a resident card first [2].
• The e.firma is the SAT's digital signature. You get it at an SAT office by appointment, with fingerprints, an iris scan and a USB drive [3].
• None of this replaces your US obligations. You still file with the IRS and report Mexican accounts on the FBAR [4].

The CURP: your ID number

What it is

The CURP is an 18-character alphanumeric code. The first 16 come from your identity document (for foreigners, the immigration document), and the last two are assigned by the National Population Registry (RENAPO) [1]. It's used to register people who live in Mexico, and you can look it up and print it at gob.mx/curp [1].

You'll be asked for it at the bank, by a new employer, for health insurance enrollment, at your kid's school, for many government apps and often by landlords.

How residents get one

1. Get your resident card first. Tourists generally can't get a CURP; it's tied to a migration document [1].
2. Check your card. INM generally assigns a CURP during the residency process, and many resident cards show it on the card itself.
3. Look yourself up at gob.mx/curp using your name and date of birth, or the code from your card [1]. Print or save the PDF; offices like a fresh printout.
4. If you can't find it or it's wrong, ask INM to issue or correct it. Name mix-ups are common when Americans have a middle name, two surnames or none, so make sure the CURP matches your passport exactly.

CURP vs your US Social Security number

One heads-up for Americans: Mexicans share their CURP far more casually than you'd ever share an SSN back home in the States. That's normal here. Keep your SSN as private as ever, though Mexican banks will still ask for your US taxpayer ID for FATCA reporting.

The RFC: your tax ID

Who needs one

The RFC is your registration with the SAT (Servicio de Administración Tributaria). Residents need one if they:

• work for a Mexican employer (your employer may register you)
• invoice Mexican clients, rent out property in Mexico or run a business
• buy or sell real estate, since notaries need it
• want proper tax receipts (facturas) for deductible expenses
• open some bank accounts or investment accounts, or sign some leases

Plenty of retirees living on Social Security and a US pension never need one for years. It still helps to have it, since more and more landlords, utilities and banks ask for it.

How to register

The SAT's own procedure sheet lays out two paths [2]:

1. Online pre-registration, then an office visit. Start on the SAT portal, then book an appointment to finish in person [2]. You need your CURP to use the full online path.
2. Straight to an office. Book an appointment (cita) online, then go in with your documents [2].

For foreigners, the key document is a valid immigration document issued by the competent authority, which in practice means your resident card [2]. You'll also need proof of your tax address (a recent utility bill or similar), an email address and your ID. Foreign residents may face extra requirements in some cases, such as naming a legal representative [2]. Ask at your appointment which apply to you.

Appointments in Mexico City can be hard to get. Check the SAT portal often, since canceled slots do open up, and be ready to take one in a different neighborhood.

Your tax regime matters

When you register, the SAT puts you in a tax regime: salaried employee, professional services, rental income and so on. Pick the wrong one and you can end up with filing obligations you didn't expect, monthly returns included. If you'll earn income in Mexico, have a Mexican accountant (contador) look at this before your appointment.

The e.firma: Mexico's digital signature

The e.firma (formerly the Firma Electrónica Avanzada) is a digital certificate tied to your RFC. You need it to file many returns, issue invoices, change your registration and handle a lot of SAT paperwork online.

What to bring to the SAT office, per the SAT's procedure sheet [3]:

1. A USB drive, where they'll save a copy of your certificate.
2. A working email address.
3. A valid official ID.
4. Your CURP.
5. For foreigners, your valid immigration document, which means your resident card.
6. Proof of tax address, if you registered for the RFC online [3].

You need an appointment, booked through the SAT portal, SAT Móvil or gob.mx [3]. At the office they take your fingerprints, a photo, an iris scan and your signature, and scan your documents [3]. You'll leave with files and a password; back them up somewhere safe. The certificate expires after several years, so put the renewal date in your calendar. Renewing before it lapses is usually far easier than starting over.

How this fits with your US taxes

Getting an RFC doesn't make you a Mexican tax resident by itself; where your home and center of life are decides that. But once you're in the Mexican system, expect it to see you:

• You still file a US return every year, no matter where you live.
• Mexican bank accounts go on the FBAR if your foreign accounts together top USD 10,000 at any time in the year. It's due April 15 with an automatic extension to October 15, filed through FinCEN's BSA E-Filing System [4].
• Mexican banks report US account holders to the IRS through FATCA, so your Mexican accounts are no secret from Uncle Sam.
• The US–Mexico tax treaty and foreign tax credits help prevent double taxation if you owe Mexican tax. A US expat tax preparer can check your situation, ideally working alongside your Mexican contador.

A quick checklist

Need a contador who works with Americans, or tips on getting a SAT appointment fast? Ask in our community group for Americans in Mexico.

Sources

1. Consulta tu CURP, Consulate of Mexico in Leamington
2. Inscripción en el RFC (ficha 39/CFF), SAT
3. Trámite de e.firma (ficha 105/CFF), SAT
4. Report of Foreign Bank and Financial Accounts (FBAR), IRS
5. Forma Migratoria Múltiple and entry information, Consulate of Mexico in the United Kingdom

Keep reading

• Mexican taxes for Americans: how they fit with your US return
• Banking in Mexico as an American
• Residente temporal or permanente: Mexico's income test
• FATCA and Form 8938 for Americans abroad