CUIL Argentina Validator

What is the CUIL/CUIT?

In Argentina, the CUIL (Código Único de Identificación Laboral) and the CUIT (Código Único de Identificación Tributaria) share the same 11-digit structure. The CUIL is used for labour and social-security matters (ANSES), while the CUIT is the tax identifier (AFIP).

Both are usually written as XX-XXXXXXXX-X: a two-digit type prefix, an eight-digit DNI and a single check digit.

Type prefixes

• 20, 23, 24, 27 — individuals. 20 is typically men, 27 women, and 23/24 resolve collisions when a DNI is shared.
• 30, 33, 34 — legal entities (personas jurídicas / companies).
• The middle 8 digits are the person's DNI (national identity document number).

Check-digit algorithm

The 11th digit verifies the other ten:

• Apply the weights [5, 4, 3, 2, 7, 6, 5, 4, 3, 2] to the first 10 digits and sum the products.
• Compute 11 - (sum mod 11).
• If the result is 11, the check digit is 0.
• If the result is 10, that DNI must use an alternate prefix (a special case rather than a digit of 10).

Common pitfalls

• Leaving the dashes in XX-XXXXXXXX-X — strip everything but digits first.
• Forgetting that a result of 11 maps to a check digit of 0.
• Producing a check digit of 10 instead of switching to the alternate prefix.
• Assuming CUIL and CUIT are different numbers — they share the format, only the administering body differs.

FAQ

Are CUIL and CUIT the same? They use the identical 11-digit layout and checksum; the CUIL is for labour/ANSES and the CUIT for tax/AFIP.

What does the prefix tell me? Whether the holder is an individual (20/23/24/27) or a company (30/33/34), and for people it hints at sex and collision handling.

Why does a check digit of 10 need a different prefix? A single digit cannot be 10, so the scheme switches to an alternate prefix (e.g. 23/24) to keep the check digit valid for that DNI.