What a CUIL and a CUIT are
In Argentina, both the CUIL and the CUIT are 11-digit identifiers, and they are calculated with exactly the same formula. What changes is who issues them and what they are for:
- The CUIL (Código Único de Identificación Laboral) is assigned by ANSES, the social-security agency, to every individual who works as an employee. It tracks pension contributions, health coverage and family benefits.
- The CUIT (Clave Única de Identificación Tributaria) is assigned by ARCA (the tax authority, formerly AFIP) to anyone carrying out a taxable activity: sole traders, the self-employed, registered taxpayers and companies. It is the number you invoice and pay taxes with.
For one individual the two numbers usually match: the CUIL you already have becomes your CUIT once you register with the tax office. This tool rebuilds that number from a DNI (the national ID) and the registered sex, entirely in your browser. Nothing is stored or sent to a server.
How the number is built
A CUIL/CUIT follows the pattern XX-DNI-D:
- Prefix (XX): two digits that depend on the type of person. For individuals it is
20(male) or27(female). The23shows up in a special case (below); companies use30,33or34. - DNI: the ID number, padded with leading zeros to eight digits.
- Check digit (D): a single digit derived from the ten digits above. It exists to catch typos.
The module-11 algorithm
The check digit is produced like this:
- Take the ten digits of prefix + DNI and multiply each one by the fixed series
5, 4, 3, 2, 7, 6, 5, 4, 3, 2. - Add up all the products.
- Take the remainder of that sum divided by 11.
- The digit is
11 − remainder. If it comes out to 11, the digit is 0. If it comes out to 10, the prefix is switched to23and the digit becomes 9.
Worked example
Take the DNI 12,345,678, male (prefix 20):
| Digit | 2 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|---|---|
| Weight | 5 | 4 | 3 | 2 | 7 | 6 | 5 | 4 | 3 | 2 |
| Product | 10 | 0 | 3 | 4 | 21 | 24 | 25 | 24 | 21 | 16 |
The products add up to 148. The remainder of 148 ÷ 11 is 5, so the digit is 11 − 5 = 6. The final number is 20-12345678-6.
If the same person were registered as female, the prefix would be 27, the sum would be 176 (a multiple of 11), the digit would be 0, and the number would be 27-12345678-0.
Why you might need it
Knowing your CUIL/CUIT lets you fill in forms, check a payslip, start a procedure or confirm that a number someone gave you has no typo. Because the check digit depends on every other digit, a single miscopied number makes the whole identifier fail validation.
Frequently asked questions
What is the difference between a CUIL and a CUIT?
The CUIL identifies employees to ANSES; the CUIT identifies taxpayers (self-employed, sole traders, companies) to ARCA. For an individual the eleven digits are the same number — only the issuing agency and the purpose differ.
Why is my prefix 20, 27 or 23?
20 corresponds to male and 27 to female. The 23 is a special case: when the calculation with 20 or 27 yields a check digit of 10 — which cannot exist, since it must be a single digit — the rules reassign the prefix to 23 and fix the digit at 9.
Is this number official?
No. It is the number that results from applying the public algorithm, and for most individuals it matches the real one. But the definitive CUIL is issued by ANSES and the CUIT by ARCA, so for any formal procedure always confirm against the official certificate.