IBAN Validator Guide: Format, Length and the Mod-97 Check
Learn how IBAN validation works in three separate steps and why each failure means something different.
What is the IBAN Validator?
Type an IBAN and this tool checks its structure, compares its length against a table for 19 common countries, and runs the mod-97 checksum used by the IBAN standard. Each problem gets its own message, so a wrong length, a bad format and a failed checksum are not lumped together. Countries outside the table are reported as not covered rather than guessed at.
How to use it
- Type the IBAN; spaces are ignored.
- Click Validate.
- Read the format, length and checksum results, each reported separately.
Worked example
For the sample GB29 NWBK 6016 1331 9268 19, the tool reports Country: GB, Expected length: 22, Checksum (mod-97): Valid and Result: Valid IBAN.
How does the mod-97 check work?
The first four characters move to the end, letters become numbers, and the whole number must leave a remainder of 1 when divided by 97. That single rule catches most transcription errors.
Frequently asked questions
Which countries does the length table cover?
GB, DE, FR, ES, IT, CH, NL, BE, IE, AE, SA, PL, TR, PT, AT, SE, NO, DK and FI. Other countries are reported as not covered, not guessed.
Does a valid IBAN mean the account exists?
No. It means the number is well formed and passes the checksum; only the bank can confirm an account.