How long is a Danish IBAN?

Exactly 18 characters. The structure is DK, two check digits, a 4-digit registration number, and a 10-digit account number. Anything shorter or longer is invalid.

What is the registration number in a Danish IBAN?

The registration number (registreringsnummer or reg-nr) is the 4-digit code identifying the bank and branch. Domestically it is written as reg-nr plus account, for example 0040 0440116243.

How does the MOD-97 check work?

The first four characters are moved to the end, each letter is replaced by a number (A=10 to Z=35), and the result is divided by 97. The remainder must equal 1 for the IBAN to be structurally valid.

Does a valid result mean the account exists?

No. MOD-97 catches typos and transposed digits but cannot confirm the account is real or open. Only the bank can confirm that.

Is my IBAN sent anywhere?

No. All validation runs locally in JavaScript. Nothing is uploaded, logged, or stored, and the tool works offline once loaded.

Denmark IBAN Validator

Danish IBANs follow an 18-character layout defined by the SWIFT IBAN Registry under ISO 13616. Domestically Danes use a 4-digit registration number plus an account number, and it is easy to drop the leading registration digits when converting to an IBAN. This validator confirms the structure instantly, entirely in your browser.

How it works

A Danish IBAN always begins with DK, followed by two check digits, a four-digit registration number, and a ten-digit account number:

DK  kk  bbbb  aaaaaaaaaa
^   ^   ^     account number (10 digits)
|   |   registration number (4 digits)
|   check digits (2)
country code

The validator runs three checks: the length must be exactly 18; the 14-digit BBAN must be all digits; and the ISO 7064 MOD-97-10 checksum must pass. For the checksum the first four characters (DKkk) are moved to the end, every letter is replaced by its numeric code, and the resulting long integer must leave a remainder of 1 when divided by 97. The computation is folded digit-by-digit so no big-integer library is needed.

Worked example

Take DK50 0040 0440 1162 43: country code DK, check digits 50, registration number 0040, account 0440116243. Rearranging the IBAN and dividing by 97 leaves remainder 1, so the checksum passes.

Tips

A common error is omitting the leading zero of the registration number, which makes the IBAN one digit short and fails the length check. Some Danish accounts are padded with leading zeros to fill the 10-digit account field, so keep those zeros when copying. All figures are processed locally and never uploaded.