IBAN Validator

An IBAN (International Bank Account Number) is not just a long string of letters and digits — the last two characters of its country code block are a real checksum, computed with the ISO 7064 mod-97 algorithm, that catches the vast majority of typos and transcription errors before a wire transfer is even submitted. This tool implements that exact algorithm rather than a lookup table or a rough approximation: it moves the first four characters of the cleaned IBAN to the end, converts every letter to its two-digit numeric value (A=10 through Z=35, so a 22-character IBAN can expand into a 30-plus digit number), and computes that large number modulo 97 using JavaScript's BigInt type, since the value routinely exceeds Number.MAX_SAFE_INTEGER for longer IBANs. A genuinely valid IBAN always reduces to exactly 1.

Checksum validity alone does not guarantee an IBAN is well-formed, so this tool also cross-checks the total length against a bundled table of 79 real IBAN-issuing countries drawn from the ISO 13616 registry — Germany's IBANs are always 22 characters, France's are always 27, Ukraine's are always 29, Malta's are always 31, and so on. If the length for a recognized country code does not match, the tool reports the mismatch explicitly rather than only saying "invalid", and if the country code is not in the bundled table it says so plainly and simply skips the length check while still verifying the mod-97 checksum.

Nothing about the process is hidden. The result panel shows the rearranged string with the country code and check digits moved to the end, the full letter-to-number expansion used to build the numeric string that gets reduced mod 97, and the exact remainder that was computed — so you can verify by hand, or against any other implementation, that the tool is not simply flashing a green checkmark on faith. A known-valid test IBAN such as GB82 WEST 1234 5698 7654 32 will walk through every step and land on a remainder of exactly 1.

Like every tool on this site, the IBAN validator runs entirely in your browser: no bank account number, real or test, is ever sent to a server, logged, or stored anywhere. Paste an IBAN, get an instant, transparent answer, and copy the full breakdown with one click for your own records or a support ticket.