What is an F-skatt and is it its own number?

F-skatt (F-tax) is an approval Skatteverket grants to people and businesses who pay their own preliminary tax and social contributions. It is not a separate number — it is tied to your existing personnummer or organisationsnummer, so validating the F-skatt means validating that underlying number.

How is the check digit calculated?

Swedish identity numbers use the Luhn (modulus-10) algorithm over the first 9 of 10 significant digits. Digits in alternating positions are doubled, digits over 9 have 9 subtracted, the products are summed, and the check digit makes the total a multiple of 10.

How do I tell a personnummer from an organisationsnummer?

An organisationsnummer always has a third digit of 2 or higher, because that position would otherwise be part of a calendar month in a personnummer. The tool uses this rule to label the detected number type automatically.

Does a valid check digit mean F-skatt is actually approved?

No. A valid check digit only confirms the number is well-formed. It does not confirm that Skatteverket has granted F-skatt status — you must verify that on the official Skatteverket approval lookup. This tool performs no external lookup.

Is my number sent anywhere?

No. The Luhn check runs entirely in your browser. The number you enter never leaves your device, which is important because Swedish identity numbers are sensitive personal data.

Sweden F-skatt Number Validator

A Swedish F-skatt (F-tax) approval is what lets a sole trader or company invoice clients and handle their own preliminary tax and social-security contributions rather than having the client deduct tax at source. Crucially, F-skatt is not a standalone identifier: it is granted by Skatteverket against an existing personnummer (for individuals) or organisationsnummer (for legal entities). So when you “validate an F-skatt reference” in a contractor-onboarding flow, you are really validating that underlying Swedish identity number. This free tool runs that exact check in your browser.

How it works

Both Swedish identity numbers carry a check digit computed with the Luhn (modulus-10) algorithm over their 10 significant digits:

Strip any century prefix and the hyphen, leaving 10 digits.
Working over the first 9 digits, double the digits in alternating positions starting from the left.
If a doubled value exceeds 9, subtract 9 from it.
Sum all nine processed values.
The 10th digit is the check digit — it is correct when (10 - (sum mod 10)) mod 10 equals it.

To decide which type of number you entered, the tool reads the third digit: an organisationsnummer always has a third digit of 2 or higher (a personnummer’s third digit is part of the calendar month and stays 0 or 1).

Example and notes

Take the organisationsnummer 556036-0793. The first nine digits 556036079 are Luhn-processed, and the result confirms 3 as the valid check digit, so the number is internally well-formed.

A passing check digit tells you the number could not contain a single mistyped or transposed digit — it does not tell you the entity exists or that F-skatt is currently approved. For that you must consult Skatteverket’s official approval lookup. Everything here runs locally, which matters because personnummer are sensitive personal data and should not be transmitted to third-party validators.