PESEL 2.1.4-rc.7

PESEL (Universal Electronic System for Population Registration in Poland)

A .NET library for PESEL number validation.

Documentation

• Validation using System.ComponentModel.DataAnnotations
• PESEL validation with FluentValidation
• PESEL number generation

Installation

The library is available on the NuGet Gallery.

Install-Package PESEL

PESEL Validation

A PESEL number can be validated using the PeselValidator class or the PeselAttribute, which can be applied to model properties.

Using PeselValidator

var validator = new PeselValidator();

var entity = new PeselEntity("02070803628");

var validationResult = validator.Validate(entity);

Assert.IsTrue(validationResult.IsValid);

The ValidationResult object also contains parsed information extracted from the PESEL number, such as gender and date of birth.

Algorithm References

• https://obywatel.gov.pl/dokumenty-i-dane-osobowe/czym-jest-numer-pesel
• https://4programmers.net/Algorytmy/PESEL_-_everything_you_need_to_know
• http://www.szewo.com/php/pesel.phtml
• http://zylla.wipos.p.lodz.pl/ut/pesel.html
• https://en.wikipedia.org/wiki/PESEL

Date of Birth Encoding

The date of birth is encoded numerically as:

YYMMDD

To distinguish between centuries, the following encoding rules are used:

• 1900–1999 → month encoded normally (01–12)
• 1800–1899 → month + 80
• 2000–2099 → month + 20
• 2100–2199 → month + 40
• 2200–2299 → month + 60

Gender

Gender information is encoded in the 10th digit (the second-to-last digit) of the PESEL number:

• 0, 2, 4, 6, 8 → female
• 1, 3, 5, 7, 9 → male

After a legal gender change, a new PESEL number is issued.

Checksum Digit and Validation

The 11th digit is a checksum digit used to detect errors. It is calculated based on the first ten digits.

Let a–j represent consecutive digits of the PESEL number. The checksum is calculated as:

9×a + 7×b + 3×c + 1×d + 9×e + 7×f + 3×g + 1×h + 9×i + 7×j

If the last digit of the result does not match the checksum digit, the PESEL number is invalid.

Example

For the PESEL number 44051401358:

9×4 + 7×4 + 3×0 + 1×5 + 9×1 + 7×4 + 3×0 + 1×1 + 9×3 + 7×5 = 169

169 % 10 = 9

Since 9 ≠ 8, the PESEL number is invalid.

Equivalent Validation Method

An equivalent method uses the following weighted sum:

1×a + 3×b + 7×c + 9×d + 1×e + 3×f + 7×g + 9×h + 1×i + 3×j + 1×k

If the last digit of the result is 0, the PESEL number is valid. Otherwise, it is invalid.

Algorithm Limitations

The checksum algorithm has known limitations:

• swapping year and day (yy-mm-dd ↔ dd-mm-yy) may produce the same checksum
• the algorithm does not validate semantic correctness of the data

Due to the checksum properties, a missing digit can sometimes be reconstructed.

Errors in PESEL Assignment

In practice, PESEL numbers with errors have existed, including:

• incorrect birth dates
• duplicated serial numbers
• incorrect gender encoding
• invalid checksum digits

Some of these issues were discovered years later during data migration. Therefore, a successful checksum validation does not guarantee that a PESEL number was officially assigned.

A PESEL number can be changed in cases such as:

• legal gender change
• issuance of a new birth certificate
• administrative errors

In 2012, administrative mistakes resulted in the same PESEL number being assigned to different individuals in approximately 2,000 cases.