PESEL Validator & Explainer

PESEL Structure

A PESEL number is an 11-digit identifier with format: YYMMDDZZZGX

• YYMMDD: Date of birth (with century offsets encoded in the month).
• ZZZG: Individual sequence number and gender.
• G: Gender digit (even/0 = female, odd = male).
• X: Checksum control digit.

Century Offsets Table

To handle different birth centuries, the month digits are modified:

• 1800 – 1899: Month + 80
• 1900 – 1999: Month + 0
• 2000 – 2099: Month + 20
• 2100 – 2199: Month + 40
• 2200 – 2299: Month + 60

Checksum Verification Formula

The checksum control digit is verified using weighted multiplication: $$\text{Sum} = (1\cdot d_1 + 3\cdot d_2 + 7\cdot d_3 + 9\cdot d_4 + 1\cdot d_5 + 3\cdot d_6 + 7\cdot d_7 + 9\cdot d_8 + 1\cdot d_9 + 3\cdot d_{10}) \pmod{10}$$ $$\text{Control Digit} = (10 - \text{Sum}) \pmod{10}$$

Valid PESEL Numbers

• 92082612336: Valid male PESEL born on August 26, 1992.
• 92082612343: Valid female PESEL born on August 26, 1992.

Invalid PESEL Numbers

• 92082612335: Invalid checksum digit (expected 6, got 5).
• 920826: Too short (must be exactly 11 digits).
• 920826abcde: Contains non-numeric characters.

Common Integration Mistakes

• Treating Month as 1-12: Developers often forget the century offset (e.g. +20 for years 2000+). A birth date in 2005-08-12 is encoded as month 28 (052812...), which causes parsing errors if not mapped properly.
• Saving as Integer: PESEL numbers can have leading zeros (e.g. born in 2000-2009). Saving them as raw integers truncates the leading digit, corrupting the length and validation. Store as VARCHAR(11).
• Ignoring the Checksum: Many legacy systems check the 11-digit length only, bypassing checksum validation, allowing typo errors.

Official Regulations & References

• Ministry of Digital Affairs (Poland): Official definition of the PESEL registry.
• Act of 24 September 2010 on Population Registration: Legal base for Polish identifiers and sequence allocations.
• PESEL Registry Specifications: Gov.pl portal guidelines for developers integrating domestic systems.

JavaScript Implementation

function validatePESEL(pesel) {
  if (!/^\d{11}$/.test(pesel)) return false;
  const weights = [1, 3, 7, 9, 1, 3, 7, 9, 1, 3];
  let sum = 0;
  for (let i = 0; i < 10; i++) {
    sum += parseInt(pesel[i]) * weights[i];
  }
  const checksum = (10 - (sum % 10)) % 10;
  return checksum === parseInt(pesel[10]);
}

Python Implementation

def validate_pesel(pesel: str) -> bool:
    if not pesel.isdigit() or len(pesel) != 11:
        return False
    weights = [1, 3, 7, 9, 1, 3, 7, 9, 1, 3]
    digits = [int(d) for d in pesel]
    sum_val = sum(d * w for d, w in zip(digits[:10], weights))
    checksum = (10 - (sum_val % 10)) % 10
    return checksum == digits[10]

Java Implementation

public class PeselValidator {
    public static boolean validate(String pesel) {
        if (pesel == null || !pesel.matches("\\d{11}")) {
            return false;
        }
        int[] weights = {1, 3, 7, 9, 1, 3, 7, 9, 1, 3};
        int sum = 0;
        for (int i = 0; i < 10; i++) {
            sum += Character.getNumericValue(pesel.charAt(i)) * weights[i];
        }
        int checksum = (10 - (sum % 10)) % 10;
        return checksum == Character.getNumericValue(pesel.charAt(10));
    }
}