The personnummer is a ten digit Number given to all Swedish residents so that they can be identified by the system. It is defined by paragraph 18 of folkbokföringslagen (1991:481). The official translation is 'Personal Identification Number'; a rather strange translation in my opinion. It is unique to every person and is used in all sorts of databases as a unique key (or whatever it's called), efficiently locking everyone without a number out of the system.

Some compare the personnummer to the American social security number, but I think that is a somewhat bad comparison since the personnummer is given to all residents but the SSN only to those who qualify for social security. (I might be wrong here)

It looks like this: 123456-7890

The first six digits are the date of birth with the year first, then month and date last. Digits 7 and 8 do not have any meaning. (Although one of them used to give place of birth.) The ninth digit gives the sex of the person, odd for men and even for women. The last digit is a checksum calculated according to the modulus-10 method. The dash is just there to separate the date of birth from the other digits and can be omitted. It is replaced with a plus (+) sign if the person is more than 100 years old.

Since the plus sign isn't stored in databases this used to create some confusion. For example, people above 100 years of age weren't allowed to withdraw money from their bank accounts (the computer system thought they were too young). This is the reason to why the numbers are stored with 12 digits (with four digits for year of birth) in most computer systems nowadays.

The number system first appeared in its current form in 1947, but then without a checksum. The checksum was added in 1967.
Many other countries, such as Russia, China and Finland use a similar system. The numbers given to organisations (juridical persons) have the same format but the digits have different meanings and the checksums do not match. It's quite useful for databases though.

The areacodes in swedish Personummers

This is a list of digit 7,8 and 9 in the swedish personnummer, which tell where the person is born.

001-139    Stockholms län (AB)
140-159    Uppsala län (C)
160-189    Södermanlands län (D)
190-237    Östergötlands län (E)
240-269    Jönköpings län (F)
270-289    Kronobergs län (G)
290-319    Kalmar län (H)
320-329    Gotlands län (I)
330-349    Blekinge län (K)
350-389    Kristianstads län (L)
390-459    Malmöhus län (M)
460-479    Hallands län (N)
480-549    Göteborgs och Bohus län (O)
550-589    Älvsborgs län (P)
590-619    Skaraborgs län (R)
620-649    Värmlands län (S)
660-689    Örebro län (T)
690-709    Västmanlands län (U)
710-739    Kopparbergs län (W)
750-779    Gävleborgs län (X)
780-819    Västernorrlands län (Y)
820-849    Jämtlands län (Z)
850-889    Västerbottens län (AC)
890-929    Norrbottens län (BD)
930-999    Used when all other numbers are used, or in case of immigration

An eleven digit number given to all Norwegian citizens either when born, upon immigration or when granted political asylum. The personnummer was introduced in 1967 together with the new social security system; Folketrygden. It was meant to help the government keep social security records in an efficient manner with the advent of computers. Together with the system came regulations on what the records could and could not be used for, some fairly strict ones to boot. The regulations are enforced by Datatilsynet, an agency tasked with making sure the privacy of Norwegian citizens are taken care of.

The six first digits denote date of birth in DDMMYY format. If you by chance are born on the same date as me, the first six digits in your personnummer would be 311267.

Next you have three digits to establish your gender. Females have even numbers and males have odd numbers. Numbers run from 100 to 999.

The two last digits are a control number, or if you like, a checksum. Since no two citizens should have the same number and all persons born on the same date should have different numbers, you cannot use the sum of the digits. That would render the checksum unusable in case you swap two numbers in e.g. the birthdate.

Instead, two keys are used. Key #1 is always 3 7 6 1 8 9 4 5 2 and key #2 is always 5 4 3 2 7 6 5 4 3 2 . Now, in order to calculate the first checksum digit, you must multiply the first nine digits in the personnummer with key #1 - one by one. The resulting numbers are added together and should be dividable by 11. If they are not, the gender number is wrong.

The second checksum digit is generated in the same way, only now you need to use the nine first digits plus the first checksum digit. Multiply the 10 digits with the digits in key #2, one by one. Add up all the numbers and check that the result is dividable by 11.

You now have a valid 11-digit Norwegian personnummer. A woman born April 6, 1958 would get the number 06045832837. This is not a real personnummer.

Problems
There's a few problems inherent in this system. First of all, if more than 899 persons are born on a single day in the kingdom of Norway, the system will break. Currently 165 new citizens are born each day (statistically speaking), so the system will work for quite a while longer.

Second, the system doesn't provide for changes. If you submit yourself to a hospital for a gender change, your personnummer will not reflect your new status. This has recently been the subject of a fairly low-key debate in Norway. If you are a transsexual, what gender should your personnummer reflect?

If you have no personnummer, you officially do not exist. Wherever you turn for services in the central or local government, the number is what they ask for. It should come as no surprise to the computer people out there that the personnummer is extensively used as an index in all sorts of databases. Hence if they cannot enter your personnummer, they cannot enter you in the database at all.

Finally, immigrants and asylum seekers granted Norwegian citizenship receive their personnummer along with their passport. Actually, it's in the passport. While staying at an asylum seeker camp waiting for your case to be handled, you are not yet a citizen and you lack a very important piece of information. In extreme cases, you could be stuck in the asylum seeker camp for years. The authorities on these things hand out temporary numbers to asylum seekers, but it's still not a real personnummer.

If someone asks you for your personnummer and they're not on the job for a government agency, local government office, social services or the military, deny them the information. Having your number unlocks lots and lots of information in various databases and enables people with the right access to do crosschecks on you. I usually give them the first six digits (my date of birth, commonly called the "birth number") and play dumb for the next three minutes.

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