IBAN Validator
Validate an IBAN's country length and ISO 13616 mod-97 checksum.
Overview
An IBAN (International Bank Account Number) is the standardized format used to identify bank accounts across most of Europe, parts of the Middle East, and a growing list of other countries. The standard, ISO 13616, defines a country-specific length (between 15 and 34 characters), a two-letter country code, two check digits, and a domestic Basic Bank Account Number (BBAN). A validator confirms the length is correct for the country and that the embedded mod-97 checksum is intact.
Validation catches a substantial fraction of typing errors before a SEPA or wire payment is submitted, where a corrected mistake can take weeks and recall fees to unwind. It does not, however, confirm that the account exists or that the name on the wire matches the named beneficiary. For high-value transfers always use Confirmation of Payee (CoP) or a small test transaction.
How it works
First, look up the expected length for the country code and confirm the input matches. Then rearrange: move the first four characters (country + check digits) to the end of the string. Replace each letter with two digits using the rule A = 10, B = 11, … Z = 35. The resulting all-numeric string is treated as a single very large integer; the check is that this integer modulo 97 equals 1. To avoid overflow, the modulo is computed digit-by-digit using the property (remainder × 10 + next_digit) mod 97.
Examples
GB82 WEST 1234 5698 7654 32— UK, 22 characters as required. Mod-97 evaluates to 1.DE89 3704 0044 0532 0130 00— Germany, 22 characters. Valid checksum.FR14 2004 1010 0505 0001 3M02 606— France, 27 characters. Valid.GB82 WEST 1234 5698 7654 33— same UK IBAN with the trailing digit changed. Mod-97 returns a value other than 1, so it fails.XX12 3456 7890— invalid country code, rejected on the length lookup step.
FAQ
Are IBANs case-sensitive?
No. The standard letters are upper case, but validators should normalize to upper case before processing.
Why are some IBANs 34 characters long?
Countries with longer domestic account schemes (Malta, Saint Lucia) need more digits in the BBAN portion.
Does the IBAN encode the bank?
The first few characters of the BBAN typically include a bank code and branch code, but the format varies by country.
Can I tell a real account from a valid format?
No. The checksum is a typing-error filter, not an account lookup. Only a payment attempt or CoP confirms existence.
Do US banks use IBANs?
No — the US uses routing numbers (ABA) and account numbers. International wires to or from the US still rely on SWIFT BIC plus the domestic identifiers.