IBAN Validator

An IBAN packs three things into one string: a two-letter country code, two check digits, and a country-specific basic bank account number. Validation is two independent steps, and this tool runs both. First the length is compared against the country's published specification — Norway's IBANs are 15 characters, Germany's and the United Kingdom's are 22, France's and Italy's are 27, Saint Lucia's are 32, and the table here covers 89 countries. Then the checksum: move the first four characters to the end, replace each letter with a number (A = 10 through Z = 35), and the whole thing read as one long integer must leave a remainder of 1 when divided by 97.

That mod-97 scheme, ISO 7064, is chosen because of what it catches rather than what it computes. Any single wrong character fails it, and so does any transposition of two adjacent digits — the two mistakes people actually make when copying an account number off a screen or hearing it over the phone. What it does not do is guarantee correctness: a thoroughly scrambled string still has roughly a one-in-97 chance of landing on a valid remainder by accident.

The larger limit is that a valid IBAN is not a real one. The checksum tells you the string is internally consistent. It cannot tell you that the bank code belongs to a bank that exists, that the account is open, or that it belongs to the person you think it does. Many countries also embed their own national check digits inside the BBAN — Spain, Italy, France and Belgium among them — and the mod-97 pass says nothing about those. For an actual payment you still need the bank's confirmation, and increasingly a confirmation-of-payee check on the name.

Everything runs in your browser and nothing is transmitted, which is the point when the string you are checking is a real account number. Spaces are ignored and letters are upper-cased before validation, so you can paste an IBAN formatted in the conventional four-character groups straight from an invoice; the output shows the parsed country, the check digits, the BBAN, and the grouped form to copy back.