What is a PESEL number?

PESEL stands for Powszechny Elektroniczny System Ewidencji Ludnosci — Poland's universal electronic population register. Every Polish citizen and registered foreign resident receives an 11-digit PESEL at birth or registration. It is used on all government documents, tax returns, healthcare cards, and most official forms in Poland.

How does the PESEL checksum work?

The first 10 digits are each multiplied by a fixed weight from the sequence 1, 3, 7, 9, 1, 3, 7, 9, 1, 3. The products are summed. The check digit (position 11) must equal (10 minus (sum mod 10)) mod 10. The mod-10 at the end handles the edge case where the remainder is 0, keeping the check digit in the range 0-9.

How is the birth date encoded in a PESEL?

Digits 1-2 (YY) give the last two digits of the birth year. Digits 3-4 (MM) encode both the month and the century: values 01-12 map to the 1900s (plain month), 21-32 to the 2000s (subtract 20), 81-92 to the 1800s (subtract 80), 41-52 to the 2100s (subtract 40), and 61-72 to the 2200s (subtract 60). Digits 5-6 (DD) give the day.

How is gender encoded?

Digit 10 (the second-to-last digit, often called the "C" digit) encodes gender. An odd digit (1, 3, 5, 7, 9) means male; an even digit (0, 2, 4, 6, 8) means female. Digits 7-9 together with digit 10 form a four-digit serial that distinguishes individuals born on the same day.

Does a valid checksum mean the PESEL belongs to a real person?

No. This tool performs a purely structural check. A PESEL that passes the checksum and encodes a real calendar date is correctly formatted, but only the Polish Ministry of Digital Affairs registry can confirm whether it was ever issued to a living person. Use this tool to catch typos and format errors, not to verify identity.

Completely. Every calculation happens inside your browser using JavaScript. No digits, results, or metadata are ever sent to any server. You can even disconnect from the internet and the validator will continue to work.

Poland PESEL Validator

The Poland PESEL validator checks whether an 11-digit PESEL number is structurally correct. It runs the official weighted checksum, tells you exactly why the number passes or fails, and decodes every piece of information the format encodes — birth date (including century), and gender. Everything happens locally in your browser; no data is ever transmitted.

What is a PESEL?

PESEL (Powszechny Elektroniczny System Ewidencji Ludności) is Poland’s national population register number, introduced in 1979. Every Polish citizen receives one at birth; foreign nationals who register their residence in Poland also receive one. The number appears on the national identity card (dowód osobisty), passport, tax return, and health insurance card. Because it encodes the holder’s date of birth and gender, it is both an identifier and a compact data record.

Structure of the 11 digits

A PESEL looks like YYMMDDSSSCP, where each group carries a specific meaning:

Positions	Label	Meaning
1-2	YY	Last two digits of birth year
3-4	MM	Month, offset-encoded to carry century
5-6	DD	Day of birth (01-31)
7-9	SSS	Serial number within the birth date
10	C	Gender digit (odd = male, even = female)
11	P	Weighted check digit

Century encoding in the month field

The clever part of PESEL is that the two-digit month field encodes five different centuries by adding a fixed offset:

Raw MM value	Real month	Century
01-12	plain	1900s
21-32	subtract 20	2000s
81-92	subtract 80	1800s
41-52	subtract 40	2100s
61-72	subtract 60	2200s

So a person born on 14 May 2000 would have MM = 25 (May + 20) and their PESEL starts 00 25 14 …. A person born on 14 May 1944 would have MM = 05 and their PESEL starts 44 05 14 ….

The checksum algorithm

The check digit at position 11 is computed using a weighted sum over the first 10 digits with the repeating weight pattern 1, 3, 7, 9, 1, 3, 7, 9, 1, 3:

Multiply each of the first 10 digits by its corresponding weight.
Add all 10 products together.
Compute sum mod 10.
Subtract from 10, then take mod 10 again (the second mod handles the case where the remainder is already 0, keeping the result in 0-9).
The result must equal digit 11.

For the obviously-fake sample 44051401359: weights × digits sum to 191, 191 mod 10 = 1, (10 − 1) mod 10 = 9 — which matches the last digit. Expand “Show checksum working” inside the tool to see the full multiplication table for any number you enter.

Example

The sample number 44051401359 is constructed purely to demonstrate a valid format — it is not a real person’s PESEL:

Birth date: 14 May 1944 (MM=05, in the 1900-range; DD=14; YY=44)
Gender digit: 5 (odd → Male)
Checksum: position-11 digit is 9, expected value is 9 — pass

Any number where one digit is wrong will fail the checksum check, and the tool will show both the expected and actual values so you can pinpoint the error immediately.