Question 1

What is an IBAN and what does it contain?

Accepted Answer

IBAN (International Bank Account Number) is an internationally agreed standard (ISO 13616) for identifying bank accounts. It starts with a 2-letter country code (GB, DE, FR), followed by 2 check digits, then the BBAN (Basic Bank Account Number) which is country-specific. Example: GB82 WEST 1234 5698 7654 32. The total length varies by country: UK IBANs are 22 characters, German IBANs are 22, French are 27. IBANs are used for SEPA transfers within Europe and increasingly in international wire transfers.

Question 2

How is the IBAN checksum calculated?

Accepted Answer

The IBAN check digit validation uses MOD-97: (1) Move the first 4 characters to the end of the IBAN. (2) Replace each letter with digits (A=10, B=11, ..., Z=35). (3) Calculate the numeric string modulo 97. (4) If the result is 1, the IBAN is valid. Example: GB82WEST12345698765432 → WEST12345698765432GB82 → convert letters → compute mod 97 → must equal 1. This detects single digit errors and most transposition errors.

Question 3

What is the difference between IBAN and BIC/SWIFT?

Accepted Answer

IBAN identifies the bank account (account number + bank + country). BIC (Bank Identifier Code) / SWIFT code identifies the bank itself (not the account): a 8 or 11 character code like DEUTDEFF (Deutsche Bank Germany) or BARCGB22 (Barclays UK). For SEPA transfers within the EU, only the IBAN is required. For international SWIFT transfers, both IBAN and BIC are typically needed. BIC format: 4-letter bank code + 2-letter country + 2-character location + optional 3-character branch.

Question 4

Is IBAN validation enough to verify a bank account exists?

Accepted Answer

No — IBAN validation only verifies the format and checksum. A structurally valid IBAN may still refer to an account that does not exist, has been closed, or belongs to a different person. To verify an account exists, you need a bank-level verification service (like open banking APIs, Plaid, or a payment processor's verification endpoint). IBAN validation is a necessary first step to catch typos, but it is not a substitute for account existence verification.

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