CPF Validator

The CPF (Cadastro de Pessoas Físicas), Brazil's individual taxpayer registry number, is made up of 11 digits. The first nine form the base number, where the 9th digit indicates the region in which the CPF was originally issued, and the last two are the check digits (Dígitos Verificadores, or DV). These digits are calculated to reduce typing errors and validate the consistency of the number. The calculation is based on the Modulo 11 algorithm, widely used in identification systems. On this page, you can enter a CPF and instantly check whether its check digits are valid according to that algorithm.

1. Calculating the First Check Digit

The calculation of the first check digit (the 10th digit of the CPF) uses only the first nine digits of the base number.

• Multiply the first digit by 10, the second by 9, the third by 8, and so on, until the ninth digit is multiplied by 2.
• Add up all the results of the multiplications.
• Divide the sum by 11 and take the remainder.
• If the remainder is less than 2, the first check digit is 0.
• Otherwise, the first check digit is 11 minus the remainder.

2. Calculating the second check digit

The calculation of the second check digit (the 11th digit of the CPF) follows the same process, but now uses the nine digits of the base number plus the first check digit, totaling 10 digits.

• Multiply the first digit by 11, the second by 10, the third by 9, and so on, until the first check digit is multiplied by 2.
• Add up all the results of the multiplications.
• Divide the sum by 11 and take the remainder.
• If the remainder is less than 2, the second check digit is 0.
• Otherwise, the second check digit is 11 minus the remainder.

Practical example in JavaScript

Below is a common, optimized JavaScript function to validate both check digits of a CPF:

One detail before looking at the code: above, the rule was presented as "if the remainder of the division by 11 is less than 2, the digit is 0". In the code, the logic appears differently: first 11 - (sum % 11) is calculated, and then the results 10 and 11 are converted to 0. Although they look like different approaches, both implement exactly the same rule. The second form is simply the most common one in implementations of this algorithm.

function validateCPF(cpf) {
  if (typeof cpf !== 'string') {
    return false;
  }

  cpf = cpf.replace(/\D/g, '');

  if (cpf.length !== 11 || /^(\d)\1{10}$/.test(cpf)) {
    return false;
  }

  let sum = 0;

  // First check digit
  for (let i = 0; i < 9; i++) {
    sum += Number(cpf[i]) * (10 - i);
  }

  let digit = 11 - (sum % 11);
  if (digit > 9) digit = 0;

  if (digit !== Number(cpf[9])) {
    return false;
  }

  // Second check digit
  sum = 0;

  for (let i = 0; i < 10; i++) {
    sum += Number(cpf[i]) * (11 - i);
  }

  digit = 11 - (sum % 11);
  if (digit > 9) digit = 0;

  return digit === Number(cpf[10]);
}

CPF 9th Digit by Fiscal Region

The 9th digit of every CPF corresponds to the fiscal region where the document was issued. Check the table below for the region matching each numeric code: