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Denmark IBAN Validator

Validates a Danish IBAN: the mod-97 checksum, the 18-character length and the structure, with the registreringsnummer identified.

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In short A Danish IBAN is exactly 18 characters: DK, two check digits, then 4 digits, then 9 digits, then 1 digits — so the 4 characters after the check digits are the registreringsnummer — 0040 in the example — and the remaining 10 are the account number, 0440116243. The four digits after the check digits are the registreringsnummer, the same four-digit bank identifier Danes quote domestically. Greenland and the Faroe Islands use the identical format under their own country codes. The checksum is ISO 7064 MOD-97-10: move the first four characters to the end, turn each letter into its position in the alphabet plus nine, and read the result as one long number, which must leave remainder 1 when divided by 97. That catches every single-character mistake and almost every swap of two neighbouring characters, which is what it was designed for and why an IBAN is worth checking before you pay rather than after. What it cannot do is tell you the account exists, is open, or belongs to the person you think — a random string of the right shape passes about once in 97 tries, and no amount of arithmetic reaches into a bank. This page runs entirely in your browser, so the number you type is not sent anywhere.

How to use the Denmark IBAN Validator

  1. Paste the Danish IBAN — spaces and dashes are fine.
  2. Read the three checks: mod-97, length and structure.
  3. If it fails, the page says which check failed and what that usually means.

About the Denmark IBAN Validator

Checks a Danish IBAN three ways — checksum, length and structure — and says which of the three failed when one does, because they mean different things.

What people use it for

  • Checking a Danish IBAN before sending money to it.
  • Finding the registreringsnummer inside an IBAN you have been given.
  • Confirming a Danish number was typed or pasted correctly.

Details

Length18 characters, always
Structure4!n9!n1!n after the check digits
In wordsDK, 2 check digits, then 4 digits, then 9 digits, then 1 digits
Registreringsnummer4 characters — 0040 in the example
ExampleDK50 0040 0440 1162 43
Check digitsAlways between 02 and 98. 00, 01 and 99 cannot occur
PrivacyThe arithmetic runs in your browser. Nothing you type is sent anywhere

The maths behind it

This tool uses ISO 7064 MOD-97-10 — move the first four characters to the end, replace each letter with its position plus nine, and a valid IBAN leaves remainder 1 on division by 97. On top of that, Danish IBANs are exactly 18 characters and follow 4!n9!n1!n. Every intermediate value is shown on screen, so the result can be checked by hand.

Three checks, reported separately on purpose. A length error means a character is missing or extra, a structure error means a letter sits where a digit belongs, and a checksum failure with both of those right means a genuine typo inside the number — most often two neighbouring characters swapped.

Where this tool stops

It checks arithmetic and shape. It cannot tell you the account exists or who it belongs to, it does not look the bank up, and it does not verify any national check digits Denmark may use inside its own account number — those are separate rules, computed differently, and passing mod-97 says nothing about them.

Frequently asked questions

How many characters is a Danish IBAN?
Exactly 18, with no exceptions. After the two check digits the structure is 4!n9!n1!n — 4 digits, then 9 digits, then 1 digits. A number of any other length is not a Danish IBAN, whatever else about it looks right.
Is a Danish IBAN the same as reg. nr. plus account?
Yes — it is exactly the four-digit registreringsnummer and the ten-digit account number with DK and two check digits in front. Nothing is added or rearranged.
Where is the bank code in a Danish IBAN?
The 4 characters after the check digits are the registreringsnummer — 0040 in the example — and the remaining 10 are the account number, 0440116243.
Does a valid checksum mean the account exists?
No, and this is the thing worth taking away. Mod-97 proves the number is internally consistent — that it was probably typed correctly. It says nothing about whether the account is open, or whose it is. A random string of the right length passes about once in every 97 attempts. Only the bank can confirm the rest.
Is it safe to paste an IBAN here?
The checking happens in your browser and the number is never sent to a server — there is no request to make one. An IBAN is not a secret the way a card number is, since it is printed on every invoice you send, but it is still yours, and it does not leave your machine here.
Is the Denmark IBAN Validator free, or is there a paid tier?
Free, unlimited, and no email address required. You can use it a hundred times a day and nothing changes.
Does anything I enter leave my computer?
No. The Denmark IBAN Validator runs entirely in your browser using JavaScript. Because the work happens locally, the tool also keeps working if your connection drops, and closing the tab is all it takes to discard everything.
How is the result calculated?
It uses ISO 7064 MOD-97-10 — move the first four characters to the end, replace each letter with its position plus nine, and a valid IBAN leaves remainder 1 on division by 97. On top of that, Danish IBANs are exactly 18 characters and follow 4!n9!n1!n. The full working is printed under the result, so you can follow every step rather than trusting a black box.
What is the Denmark IBAN Validator used for?
The jobs it is built for: checking a Danish IBAN before sending money to it. Finding the registreringsnummer inside an IBAN you have been given. Confirming a Danish number was typed or pasted correctly. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
When is the Denmark IBAN Validator not the right tool?
It checks arithmetic and shape. It cannot tell you the account exists or who it belongs to, it does not look the bank up, and it does not verify any national check digits Denmark may use inside its own account number — those are separate rules, computed differently, and passing mod-97 says nothing about them. Knowing where a tool stops being trustworthy matters more than the cases where it works.
Which values should I know?
Length is 18 characters, always. Structure is 4!n9!n1!n after the check digits. In words is DK, 2 check digits, then 4 digits, then 9 digits, then 1 digits. These are printed on the page itself, so you do not have to take them on trust.
Does the Denmark IBAN Validator work on a phone?
Yes. The page is responsive and the tool works in Chrome, Safari, Firefox, Edge and Samsung Internet on both Android and iOS. There is no app to install and nothing to sign into.

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