For those of you that want a quick summary of how the Swedish ID number is created… here we go..
1. The personal identity number consists of 10 digits and a hyphen.
2. The first six correspond to the person’s birthday, in YYMMDD form.
3. They are followed by a hyphen.
4. The seventh through ninth are a serial number.
5. An odd ninth number is assigned to males
6. and an even ninth number is assigned to females.
7. The tenth digit is a checksum which was introduced in 1967 when the system was computerised.
Up to 1990, the seventh and eighth digits were correlated with the county where the bearer of the number was born or (if born before 1947) where he/she had been living, according to tax records, on January 1, 1947, with a special code (usually 9 as 7th digit) for immigrants.
Everyone however keeps their number and it is not hard to find out someone’s number if you know the birth date, the birth county and the checksum algorithm. Even easier is to call the tax authority and ask, since the personal identity number is public information.