What information does a PESEL contain?

A PESEL is 11 digits — the first six encode the date of birth (with the month offset carrying the century), the next four are a serial whose tenth digit encodes sex (odd = male, even = female), and the last digit is a checksum.

How is the PESEL check digit computed?

Multiply the first ten digits by the weights 1,3,7,9,1,3,7,9,1,3, sum them, take the sum modulo 10, and the check digit is (10 minus that) modulo 10.

Does my PESEL leave my device?

No. Everything runs entirely in your browser with client-side JavaScript — your PESEL is never uploaded or stored.

Poland PESEL Decoder

Polish PESEL decoder

A Polish PESEL packs a lot of information into 11 digits: the date of birth, the person’s sex, and a check digit. This decoder reads the embedded date (the month field is offset to encode the century), determines the sex from the tenth digit, and verifies the modulo-10 checksum.

Everything runs in your browser, so the PESEL you enter is never uploaded. This is a structure and checksum decoder only — it does not confirm the number exists in the official PESEL register.