How is gender encoded in a CPR number?

The last of the ten digits encodes gender — an odd final digit means male and an even final digit means female.

What does the CPR number format DDMMYY-SSSS mean?

The first six digits are the date of birth as day, month and two-digit year. The four-digit serial that follows distinguishes people born on the same day; its first digit helps fix the century and its last digit gives gender by parity.

How is the birth century determined?

The century comes from the 7th digit (the first serial digit) combined with the two-digit year. For example, serial digits 0-3 mean the 1900s; 4 or 9 mean 2000-2036 for years 00-36, otherwise the 1900s; and 5-8 mean 2000-2057 for years 00-57, otherwise the 1800s.

How accurate is the modulus-11 control?

The CPR Office officially abandoned the modulus-11 control on 1 October 2007 because the number space was exhausted, so a CPR that fails the modulus-11 check can still be a real, valid number. The decoder reports it only as a legacy hint.

Does this validate a CPR against the official register?

No. It only interprets the structure of the digits you enter — date of birth, gender and century. It never contacts any government database and cannot confirm that a CPR number actually belongs to a real, registered person.

Is my CPR number sent anywhere?

No. The decoder is privacy-first — all processing happens locally in your browser and the CPR number never leaves your device.

Denmark CPR Number Decoder

Denmark CPR number decoder

Decode a 10-digit Danish CPR number (personnummer), written as DDMMYY-SSSS. It reveals the structural information encoded in the number — date of birth, gender and birth century — for anyone learning how the Danish personal identification system is built.

How it works

A CPR number packs three pieces of information into ten digits:

DDMMYY — the date of birth (day, month, two-digit year).
Birth century — derived from the 7th digit (first serial digit) plus the year, using the official CPR century table. Serial 0-3 → 1900s; 4 or 9 → 2000-2036 (years 00-36) else 1900s; 5-8 → 2000-2057 (years 00-57) else 1800s.
Gender — the parity of the last digit: odd = male (mand), even = female (kvinde).

The tool also runs the historical modulus-11 control (a weighted checksum) but treats it only as a legacy hint, because Denmark officially abandoned it on 1 October 2007.

Example

For 010203-4567:

Field	Value
Date of birth	1 February 2003
Serial	4567
Century rule	serial digit 4, year 03 → 2003
Gender	last digit 7 (odd) → Male

It is privacy-first: nothing leaves your browser, and the decoder only interprets the structure of the number — it does not check it against any government register.