PESEL Validator

A PESEL for someone born in 2005 shows a month of 25, and that is correct

The first six digits look like a date, but the month field also carries the century. Add 20 for the 2000s, 40 for the 2100s, 80 for the 1800s. So a child born in May 2005 has 25 where you expect 05, and software that validates the month as 1 to 12 rejects every Pole born this century.

How it works

• Checks the eleventh digit against the weighted checksum of the first ten.
• Decodes the birth date, undoing the century offset hidden in the month.
• Reads the recorded sex from the parity of the tenth digit.

weights 1 3 7 9 1 3 7 9 1 3 applied to digits 1-10
check digit = (10 − sum mod 10) mod 10

month field: +0 1900s · +20 2000s · +40 2100s · +60 2200s · +80 1800s
tenth digit: odd = male, even = female

Worked example

The worked example from the published specification.

1. digits 1234567890 against the weights give 1+6+21+36+5+18+49+72+9+0 = 217
2. 217 mod 10 = 7, so the check digit is 10 − 7 = 3
3. 12345678903 is therefore valid and 12345678901 is not
4. a birth month of 25 decodes to May 2005, not an error
5. a tenth digit of 5 records male; 4 would record female

Eleven digits that carry a date, a sex, a serial number and a checksum. The century trick is the part that breaks naive validators, because the month can legitimately read anything from 01 to 92.

Reading the result

• A passing checksum means well formed, never issued. Only the register can say whether a PESEL belongs to a real person, and this page has no access to it — nor should it.
• The number reveals date of birth and sex on its face, which is why it counts as personal data under the GDPR. Treat one you have been given with the same care as any other identifying document, and avoid pasting real numbers into tools you do not control.
• No generator is offered here. A well-formed PESEL is exactly what a fraudulent form needs, and unlike a company tax number there is no legitimate reason to synthesise a personal identifier.
• The checksum catches every single-digit error, which is what it exists for. It cannot catch two errors that happen to cancel, so a number that passes is evidence of careful typing rather than proof of authenticity.

Common questions

Is a valid PESEL proof that the person exists?

No. A pass means the eleven digits are consistent with each other: the check digit matches and the encoded birth date is a real date. Whether the number was ever issued is recorded only in the PESEL register, which has no public lookup and which this tool cannot access. To confirm someone’s identity, check an identity document or go through an institution that has access to the register.

Why does my PESEL fail validation?

Either the eleventh digit does not match the weighted sum of the first ten, which usually means a mistyped digit, or the first six digits do not form a real date. Check that you entered exactly eleven digits; spaces and dashes are ignored. A month field between 21 and 32 is not an error — that is how births from 2000 onwards are written, and this tool decodes it correctly.

How do I read the date of birth from a PESEL for someone born after 2000?

The first six digits are year, month and day, but the month also carries the century: 20 is added for 2000–2099, 80 for the 1800s and nothing for the 1900s. So a number starting 052514 means 14 May 2005, not an impossible month 25. The tenth digit records sex — odd for male, even for female — and the tool shows both after a successful check.