How IBAN Validation Works
An IBAN consists of a two-letter country code, two check digits, and a Basic Bank Account Number (BBAN). Validation uses the MOD 97 algorithm defined in ISO 13616: the country code and check digits are moved to the end, letters are converted to numbers (A=10, B=11, ...), and the resulting number must give a remainder of 1 when divided by 97.