IBAN Validator

IBAN validator (mod-97)

An IBAN (International Bank Account Number) is the standard format for identifying a bank account across borders for SEPA and international transfers. Getting one digit wrong can send money to the wrong place, so before you save or share an IBAN it is worth checking that the built-in checksum agrees with the rest of the number. This validator does that instantly and entirely offline.

How it works

The tool follows the ISO 13616 mod-97 procedure:

1. Strip spaces and uppercase the input. An IBAN is [CC][2 check digits][account block].
2. Move the first four characters (country code + check digits) to the end.
3. Replace each letter with two digits: A=10, B=11 … Z=35.
4. The IBAN is valid when this large integer mod 97 equals 1.

To avoid huge numbers, the mod-97 is folded digit by digit across the string. The tool also compares the total length against the expected length for the detected country.

Example

Validate the test IBAN GB82 WEST 1234 5698 7654 32:

• Move GB82 to the end → WEST12345698765432GB82.
• Expand letters → W=32, E=14, S=28, T=29 … G=16, B=11.
• The resulting integer mod 97 = 1 → valid, and the length (22) matches GB.

Selected IBAN lengths

Privacy: the mod-97 calculation runs entirely in your browser. Your IBAN is never uploaded or stored, and a pass confirms internal consistency, not that the account is open.