CUIL and CUIT check digit:
Argentina

The parts of a CUIL or CUIT

• Prefix: 20, 23, 24 or 27 for people, and 30, 33 or 34 for companies and other organisations.
• The 8-digit DNI number (with leading zeros if needed).
• A check digit from 0 to 9.

Prefixes no longer show sex or gender

Older CUILs usually start with 20 for men and 27 for women. Since Resolución General Conjunta 5007/2021 of AFIP and ANSES, people’s prefixes (20, 23, 24 and 27) are assigned at random and don’t indicate sex or gender. So use the prefix that appears on your own CUIL or CUIT rather than guessing it.

How the check digit is calculated

1. Write the prefix and the DNI as 10 digits, for example 20 12345678.
2. Multiply them by 5, 4, 3, 2, 7, 6, 5, 4, 3, 2 and add the results.
3. Take 11 minus the remainder of dividing the sum by 11. A result of 11 means the digit is 0.
4. A result of 10 can’t be written as one digit. In that case, under the usual method, the number uses prefix 23 (33 for companies) instead, and the digit is calculated again.

Where this method comes from

This is the module 11 calculation used by banks, payroll software and validation libraries. AFIP and ANSES don’t publish the formula itself, so treat a result as a check for typing mistakes, and confirm your official number with ANSES or the tax agency if a form rejects it.