A basic bank account number (BBAN) is the domestic identifier of a bank account in countries that use the International Bank Account Number standard. It contains whatever a country's banks need to locate an account, typically a bank code, sometimes a branch code, the account number and, in some countries, national check digits. Placed after a two-letter country code and two IBAN check digits, the BBAN forms the full IBAN.
The BBAN is defined by the international standard ISO 13616, which leaves each country free to set its own BBAN length and layout as long as it is fixed for that country. SWIFT acts as the registration authority and publishes every country's format in the IBAN registry. Many people never see the term, because in daily life the BBAN appears in national form: in the UK as a sort code plus account number, in Germany as a bank code plus account number. It should not be confused with the bank identifier code, which identifies the bank rather than the account.
The BBAN in plain terms
Think of a postal address. Inside a country, people write a street, house number and town in a familiar local format. To send a letter abroad, they add the country name at the bottom so foreign post offices know where to route it.
The BBAN is the local address of a bank account. It is written the way that country's banks have always done it. The IBAN simply adds the country code and a pair of check numbers to the front, turning the local address into an international one that any bank in the world can read and check for typing mistakes.
Structure inside an IBAN
Every IBAN has the same outer shell and a country-specific BBAN inside it:
- Country code. Two letters from ISO 3166, such as GB, DE or PK.
- IBAN check digits. Two digits calculated over the whole number to catch errors.
- BBAN. Up to 30 alphanumeric characters, with a fixed length and layout per country, so a full IBAN is at most 34 characters.
| Country | BBAN length | BBAN layout | Full IBAN length |
|---|---|---|---|
| United Kingdom | 18 | 4-letter bank code, 6-digit sort code, 8-digit account number | 22 |
| Germany | 18 | 8-digit bank code (Bankleitzahl), 10-digit account number | 22 |
| Pakistan | 20 | 4-letter bank code, 16-character account number | 24 |
Some national formats include their own check digits inside the BBAN, for example in France, Spain and Italy, in addition to the IBAN-level check.
How the check digits protect the BBAN
The IBAN check digits are calculated with the ISO 7064 MOD 97-10 method. The BBAN is moved in front of the country code and "00", letters are replaced by numbers (A = 10, B = 11 and so on up to Z = 35), and the check digits are:
Here is the long number produced by that rearrangement, and means the remainder after dividing by 97. Take the sample UK BBAN WEST12345698765432. Rearranged as WEST12345698765432GB00 and converted, it becomes 3214282912345698765432161100, which leaves a remainder of 16 when divided by 97. The check digits are , so the IBAN is GB82WEST12345698765432. To validate an IBAN, a system moves the first four characters to the end, converts letters and confirms the remainder is exactly 1; tools such as an IBAN checker do this automatically. The test catches nearly all single typing errors and swapped digits, but it cannot confirm the account exists or belongs to the named payee.
Where the BBAN is used
Domestic payment systems often still route on BBAN elements. UK Bacs and Faster Payments use the sort code and account number, while euro payments under SEPA require the full IBAN, even within a single country. Cross-border transfers sent over SWIFT, including MT103 and ISO 20022 messages, carry the IBAN where the receiving country uses one. Banks and payment providers derive the bank and branch from the BBAN to route a credit transfer, and an IBAN lookup can map it to a BIC.
Countries outside the IBAN system use their own domestic identifiers instead, such as the US ABA routing number plus account number. In Pakistan, the State Bank of Pakistan issued IBAN guidelines in 2012 and phased in their use for domestic electronic transfers and home remittances over the following years. Because a valid format does not prove ownership, payers increasingly rely on bank account verification and payee-name checks such as UK Confirmation of Payee and the EU's verification of payee, which became mandatory for euro credit transfers in October 2025. Errors that slip through usually surface as returned payments and payment failures.
Payment providers also issue virtual IBANs, which follow a country's BBAN format but point to a sub-ledger within a provider's master account, letting businesses give each customer a unique number for incoming payments.