Sweden Personnummer Validator

How it is calculated

The tool removes every non-digit character, so dashes, plus signs and spaces are ignored. A 12-digit entry with the century has its first two digits set aside, and anything that is not 10 digits afterwards is reported as Invalid with no check digit. The first nine digits are multiplied by the weights 2, 1, 2, 1, 2, 1, 2, 1, 2 from the left; any product above 9 has 9 subtracted (the same as adding its two digits). The products are added to a sum S, and the expected check digit is (10 − S mod 10) mod 10. The result is Valid only if that equals the tenth digit you typed and the date part is a real date: month 1 to 12 and a day within that month, or day 61 to 91 for a samordningsnummer (the real day plus 60). 29 February is accepted only in a leap year; with a 12-digit entry the full year decides, with 10 digits any year divisible by 4 is accepted. The tool also shows the expected check digit and the first six digits as YY-MM-DD. It does not test whether the number was actually issued to anyone.

Common mistakes

• Assuming Valid means the person exists. The checksum and the calendar date are tested, but not whether Skatteverket ever issued the number.
• Typing a 12-digit number and expecting the century to be fully checked. The century is only used for the leap-year rule on 29 February (200002291235 is Valid, 190002291235 is Invalid); otherwise 1981 and 2081 give the same result.
• Entering a number with a digit missing or extra. Anything that is not 10 digits (or 12 with century) is marked Invalid without a check digit.
• Expecting the plus sign used for people over 100 to change the result. Separators are ignored, so + and - are treated the same.
• Reading Invalid as a problem with the person's record when it is usually a typo. A single wrong digit anywhere in the first nine changes the expected check digit, and a day or month that does not exist fails even when the check digit matches.