IBAN (International Bank Account Number)
The IBAN is the international standard for identifying bank accounts — up to 34 characters starting with a country code and two MOD-97 check digits, defined by ISO 13616 and required for all SEPA payments.
Structure
An IBAN is country code + 2 check digits + BBAN (Basic Bank Account Number, the domestic part). Examples: AT611904300234573201 (Austria, 20 chars), DE89370400440532013000 (Germany, 22), GB29NWBK60161331926819 (UK, 22). The check digits are computed with MOD-97 — move the first four characters to the end, convert letters to numbers, and the remainder mod 97 must equal 1.
The BBAN structure is country-specific: it encodes the domestic bank code, branch, and account number in a fixed layout, which is why a validator can tell you an Austrian IBAN belongs to a specific institution just from its digits.
What validation does and does not prove
A valid checksum proves the number is well-formed and almost certainly transcribed correctly — it says nothing about whether the account exists or is open. Inside SEPA, the IBAN alone routes the payment; the BIC is optional because banks derive it.
Frequently Asked Questions
Does a valid IBAN mean the account exists?
No. The MOD-97 checksum proves the digits are well-formed — it catches typos, not closed or fictitious accounts. Reachability and account existence are confirmed by your bank, and verification-of-payee checks increasingly confirm the account holder name before you send.
Related Standards
- •ISO 13616 — IBAN
- •EPC SEPA rulebooks
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