A CURP (Clave Única de Registro de Población — Unique Population Registry Key) is an 18-character alphanumeric identifier issued by RENAPO (Registro Nacional de Población) to every Mexican citizen and legal foreign resident. It is used across government services, tax filing, healthcare, education enrolment and employment. Unlike the RFC (tax ID), the CURP is assigned at birth or on first registration and remains the same for life.

How does the CURP check-digit algorithm work?

The official RENAPO algorithm assigns each character a numeric value: digits 0-9 equal their face value; letters A-Z equal 10-35 (A=10, B=11 … Z=35); Ñ equals 36. Each of the first 17 characters is multiplied by its 1-based position (char 1 × 1, char 2 × 2, … char 17 × 17). All 17 products are summed. The remainder of that sum divided by 10 is computed: if it is 0 the check digit is 0; otherwise the check digit is 10 minus the remainder. The result must match position 18 of the CURP.

What information is encoded in a CURP?

Positions 1-4 are four letters derived from the persons name (first letter and first internal vowel of the first surname, first letter of the second surname, first letter of the given name). Positions 5-10 encode the date of birth as YYMMDD. Position 11 is H for male (Hombre) or M for female (Mujer). Positions 12-13 are a two-letter RENAPO state code for the state where the person registered. Positions 14-16 are the first internal consonants of each name component. Position 17 is an alphanumeric uniquifier assigned by RENAPO. Position 18 is the numeric check digit.

Does this tool send my CURP to a server?

No. The entire validation — format check, date parsing, state-code lookup and check-digit computation — runs in your browser using JavaScript. Nothing is transmitted to any server or stored anywhere.

A CURP can pass this validator but still be unregistered — why?

This tool verifies structural validity only. A CURP is structurally valid when it is 18 characters long, matches the official pattern, encodes a plausible date, uses a recognised state code and has the correct check digit. Whether that specific code has ever been assigned to a real person is only known to the RENAPO database, which requires an official government query (https://www.gob.mx/curp). The two checks are independent.

What are common reasons a CURP fails validation?

The most frequent errors are: (1) the wrong length — a copied CURP that dropped or gained a character; (2) an invalid date — day 00, month 13, or another impossible calendar value; (3) an unrecognised state code not in the official RENAPO two-letter list; (4) a wrong check digit — a single-character transcription error anywhere in the first 17 characters will change the expected check digit and cause this step to fail.

Mexico CURP Validator

The Mexico CURP Validator checks any 18-character CURP against the full official validation criteria published by RENAPO (Registro Nacional de Población). It is not a simple regex check — the tool runs the real check-digit algorithm, decodes every embedded data field, and explains each pass or fail in plain English. Nothing is sent to a server; all computation happens in your browser.

What is a CURP?

The CURP (Clave Única de Registro de Población) is the 18-character national identity code issued by the Mexican government to every citizen and legal resident. It appears on birth certificates, passports, tax forms, IMSS and ISSSTE health cards, university enrolment and nearly every government-issued document. Understanding how to read and verify one is essential for HR professionals, compliance teams, notaries, developers integrating with Mexican government APIs, and anyone double-checking their own documents.

CURP format — position by position

A CURP looks like this: PELJ850101HDFLNS09

Positions	Example	Meaning
1-4	PELJ	Name letters (surname vowel + surname letter + given-name letter)
5-10	850101	Date of birth YYMMDD (1 Jan 1985)
11	H	Sex: H = Hombre (male), M = Mujer (female)
12-13	DF	State of registration (DF = Ciudad de México)
14-16	LNS	First internal consonants of name components
17	0	Alphanumeric uniquifier assigned by RENAPO
18	9	Numeric check digit (the value this tool verifies)

How the check-digit algorithm works

The RENAPO specification assigns each character a numeric value:

Digits 0-9 → face value (0 through 9)
Letters A-Z → 10 through 35 (A=10, B=11, C=12 … Z=35)
Special character Ñ → 36

Each of the first 17 characters is multiplied by its 1-based position number. All 17 products are summed. The remainder of dividing the sum by 10 is calculated. If that remainder is zero the check digit is 0; otherwise the check digit is 10 minus the remainder.

Example walkthrough for position 18 of PELJ850101HDFLNS09:

Pos 1  × P(25)  = 25
Pos 2  × E(14)  = 28
Pos 3  × L(21)  = 63
Pos 4  × J(19)  = 76
Pos 5  × 8(8)   = 40
Pos 6  × 5(5)   = 30
...    (continue for all 17)
Sum = 291  →  291 mod 10 = 1  →  check digit = 10 − 1 = 9  ✓

The tool shows this full table for any CURP you enter so you can verify the working independently.

Decoded information

Beyond the checksum, the validator extracts:

Birth date — converted from YYMMDD to a full calendar date, with century inferred from the year digits relative to today.
Sex — H (male) or M (female) from position 11.
State of registration — the two-letter RENAPO code at positions 12-13 is looked up against all 32 Mexican states plus the foreign-born code NE (Nacido/a en el extranjero).
Uniquifier — position 17, an alphanumeric character that RENAPO assigns to distinguish people who would otherwise share the same first 16 characters.

Fake example (for testing)

The CURP XEXX010101HNEXXXA8 is the official RENAPO test value used in government documentation. It is deliberately constructed so it will never match a real person. Enter it above to see a full passing result with the complete checksum walkthrough.

Five things this validator checks

Length — exactly 18 characters.
Format — matches the official RENAPO regex pattern.
Date of birth — a real calendar date (not day 00 or month 13).
State code — one of the 32 official RENAPO codes (or NE).
Check digit — the RENAPO weighted-sum algorithm applied to positions 1-17.

A CURP that passes all five checks is structurally valid. Whether it is registered in the live RENAPO database is a separate question that requires an official government lookup at gob.mx/curp.