IBAN validator

Check whether an IBAN is structurally valid: the right length for its country and a passing ISO 13616 mod-97 checksum. Format validity catches typos, but it doesn’t confirm the account exists. Need it in code? Hit the IBAN API.

Call it from code

The API validates the same way and returns JSON. Authenticate with ?key= or an Authorization: Bearer header.

curl "https://www.checkfmt.com/api/v1/iban?iban=DE89370400440532013000" \
  -H "Authorization: Bearer YOUR_KEY"

How IBAN validation works

1. Strip spaces and upper-case the input.
2. Confirm the length matches the country (first two letters).
3. Move the first four characters to the end.
4. Replace each letter with two digits (A=10 … Z=35).
5. The IBAN is valid if that number mod 97 equals 1.

IBAN format by country