Mexico’s tax ID number, called the RFC (Registro Federal de Contribuyentes), is an alphanumeric code that SAT, the federal tax authority, assigns to every taxpayer. Individuals get a 13-character version built from their name and date of birth; companies get a 12-character version built from their legal name and incorporation date. You need one to receive payroll in Mexico, to issue or receive invoices, and to open a bank account, and since 2022 every Mexican adult must be registered even without any economic activity.
Who Needs an RFC
The RFC is the backbone of tax identification in Mexico. Any individual or legal entity that carries out economic activities, files periodic tax returns, or issues digital invoices must be registered. A 2022 amendment extended the obligation to all Mexican adults, so registration is now universal for residents whether or not they earn income.
Foreign nationals also fall inside the system when they work or do business in Mexico. If you are employed by a Mexican company on local payroll, your employer cannot process your salary without assigning you an RFC. Anyone acting as the legal representative of a Mexican entity must hold a personal RFC as well, which in practice means first obtaining legal residency.
How the Individual RFC Is Built
An individual RFC is a 13-character string generated from your full legal name and date of birth. The first four positions come from your name, the next six from your birth date, and the last three are a unique code called the homoclave.
- First letter: first letter of your paternal surname.
- Second letter: first interior vowel of your paternal surname.
- Third letter: first letter of your maternal surname.
- Fourth letter: first letter of your first given name.
- Digits 5 through 10: your date of birth in YYMMDD format.
- Characters 11 through 13: the homoclave assigned by SAT’s algorithm.
Take Maria Lopez Hernandez, born December 15, 1990. Her RFC starts with LOHM901215 (LO from Lopez, H from Hernandez, M from Maria) and ends with a three-character homoclave assigned by SAT, giving something like LOHM901215AB2.
How the Corporate RFC Is Built
A legal entity’s RFC is 12 characters. The structure mirrors the individual version, but the name portion uses three letters instead of four, and the date is the company’s incorporation date.
- First three letters: derived from the company’s legal name, excluding the entity-type suffix such as S.A. de C.V. or S.C.
- Digits 4 through 9: the incorporation date in YYMMDD format.
- Characters 10 through 12: the homoclave assigned by SAT.
A fictional company called Distribuidora Nacional de Alimentos, incorporated on June 5, 2003, might receive DNA030605XX1. The legal-structure suffix is always stripped before the letters are generated, so “S.A. de C.V.” never appears in the code itself.
The Homoclave and the Offensive-Word Filter
The homoclave exists because two people can easily share the same name and birthday. SAT generates it through an algorithm based on the full name, ensuring no two taxpayers end up with an identical code. You do not choose it; it is assigned automatically during registration.
The name-based portion produces one other quirk. Because the first four letters are pulled mechanically from a person’s name, some combinations spell out offensive words in Spanish. SAT keeps a published list of roughly 40 blocked four-letter combinations, and when the algorithm produces one, the final letter is replaced with an “X.” A sequence that would come out as PEDO becomes PEDX. The substitution is permanent, appears on all official documents, and has no effect on the validity of the RFC.
How to Register for an RFC
Registration begins online at the SAT portal, where you fill out the electronic form with your personal data and fiscal address. You will need your CURP (Clave Única de Registro de Población), Mexico’s general population ID number, and a recent proof of address such as a utility bill or bank statement. The address on your proof document must match what you enter on the form; mismatches are the most common reason applications stall.
After submitting the form, you book an in-person appointment through the Citas SAT system at citas.sat.gob.mx. At the local office, officials collect biometric data, including fingerprints and facial photographs. This step is required to issue your e.firma, the electronic signature used for digital filings. Once the appointment is complete, SAT issues your Cédula de Identificación Fiscal, the physical tax ID card, along with your e.firma certificate.
For a legal entity, the founding partner or legal representative files the registration using the company’s deed of incorporation (acta constitutiva), which establishes the legal name, incorporation date, and business purpose that feed into the RFC. The legal representative must already hold a personal RFC before they can register the company.
Extra Requirements for Foreign Documents
When foreign nationals or foreign-established entities register, the paperwork requirements are heavier. Any foreign document used in the process, whether a birth certificate, a passport, or a power of attorney, must be a certified copy that has been apostilled or legalized by a competent authority. Documents in any language other than Spanish need a certified translation by an authorized translator. For entities incorporated abroad, the constituent instruments must be apostilled and translated before SAT will process the file.
Generic RFC Codes Used in Invoicing
Not every transaction involves a registered taxpayer, so Mexico uses two placeholder RFCs on electronic invoices when the buyer either has no RFC or is not a Mexican tax resident.
- XAXX010101000: used for sales to the general public when the buyer is a Mexican resident who does not provide a personal RFC. Retail transactions billed to “público en general” use this code.
- XEXX010101000: used for transactions with foreign residents who do not hold a Mexican RFC.
You cannot claim tax deductions on purchases billed under a generic RFC, so anyone who needs to deduct expenses should provide their own valid RFC at the point of sale.
Keeping Your RFC Current
Registration is not a one-time event. Whenever key information changes, you must file an update notice (aviso) with SAT. A new fiscal address, a change in legal or business name, a shift in tax regime, or any modification to ownership structure all trigger the requirement. This matters because Mexico’s electronic invoicing system, CFDI in its 4.0 version, validates recipient data against SAT’s records in real time. Your RFC, legal name, fiscal domicile zip code, and tax regime must match what SAT has on file, exactly, or the invoice will be rejected during stamping. That is why businesses and individuals routinely download a fresh Constancia de Situación Fiscal, the printable proof-of-status certificate available through the SAT portal, before sharing their details with a payer.
If you stop all economic activity, you can file a notice of suspension of activities (aviso de suspensión de actividades) to pause your filing obligations without canceling the registration. The RFC itself stays permanently assigned to you; suspension only pauses what you owe SAT until you resume. Failing to file the suspension notice while also not filing returns will eventually trigger compliance alerts.