How is a CPF validated?

A CPF has 9 base digits plus 2 check digits. Each check digit is a weighted mod-11 sum of the preceding digits. The CPF is valid only when both recomputed check digits match the entered ones, and it is not an all-identical sequence.

How are the two CPF check digits calculated?

The first check digit weights the 9 base digits by 10 down to 2, sums them, takes the remainder mod 11, and the digit is 0 if the remainder is below 2, otherwise 11 minus the remainder. The second check digit repeats the process over the 9 base digits plus the first check digit, weighted 11 down to 2.

Why are CPFs like 111.111.111-11 rejected?

All-identical sequences satisfy the mod-11 maths by coincidence, so they are reserved and treated as invalid. This tool rejects every repeated-digit CPF (000... through 999...) even though the arithmetic would otherwise pass.

What is the format of a CPF?

A CPF is 11 digits written as XXX.XXX.XXX-XX. The first nine digits are the base number (with a regional digit), and the final two after the dash are the check digits. The dots and dash are formatting only — this tool accepts the number with or without them.

Does a valid CPF mean it belongs to a real person?

No. The mod-11 check only confirms the number is internally consistent. It cannot confirm the CPF is registered to anyone with Receita Federal.

Brazil CPF Validator

Q: Is my CPF sent anywhere?

No — the mod-11 calculation runs entirely in your browser. Your CPF is never uploaded, logged, or stored.

Brazil CPF validator (mod-11)

The CPF (Cadastro de Pessoas Físicas) is Brazil’s individual taxpayer number, required for nearly every formal transaction — opening a bank account, signing a contract, or filing taxes. Its last two digits are a checksum, so a single typo usually makes the whole number invalid. This validator recomputes those check digits and tells you instantly whether a CPF is well-formed, which is useful for developers, form validation, and back-office checks.

How it works

A CPF is 11 digits: 9 base digits + 2 check digits. Each check digit is a weighted mod-11 sum:

First check digit — weight the 9 base digits by 10, 9, 8 … 2, sum them, take sum mod 11. The digit is 0 if the remainder is below 2, otherwise 11 − remainder.
Second check digit — repeat over the 9 base digits plus the first check digit, weighted 11, 10 … 2.

The CPF is valid only when both recomputed digits match what was entered. Reserved all-identical sequences (like 111.111.111-11) are rejected outright.

Example

Validate 529.982.247-25:

Base digits: 529982247.
First check digit weighting (10…2) gives a remainder that maps to 2.
Second check digit weighting (11…2) over 5299822472 maps to 5.
Entered check digits 25 match → valid CPF.

Check-digit rule

Remainder (sum mod 11)	Check digit
0 or 1	0
2	9
3	8
…	11 − remainder
10	1

Privacy: the mod-11 calculation runs entirely in your browser. Your CPF is never uploaded or stored, and a valid result confirms internal consistency, not that the number is registered with Receita Federal.