Understanding International Bank Account Numbers (IBAN): How They Work

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An IBAN (International Bank Account Number) is a standardized code of up to 34 letters and digits that identifies one specific bank account, together with its country and bank, so that a payment sent across borders reaches the right place. It does not replace your domestic account number. It packages that number into an internationally readable format with a built-in error check. The standard behind it is ISO 13616, and the IBAN Registry released in July 2023 listed 86 countries using the system.

How an IBAN Is Built

Every IBAN follows the same top-level structure, read from left to right:

1. Country code (2 letters): the ISO 3166 code of the country where the account is held, such as DE for Germany, FR for France or GB for the United Kingdom.
2. Check digits (2 digits): a number calculated from the rest of the IBAN using a fixed formula (explained below). Your bank generates it, but it is not arbitrary.
3. Basic Bank Account Number, or BBAN (up to 30 characters): the domestic account details. Each country’s banking community decides what goes here, usually a bank code, often a branch or sort code, and the account number itself.

Because the BBAN is defined nationally, IBAN length is fixed per country but varies between countries. A Norwegian IBAN has 15 characters (for example NO93 8601 1117 947), a Luxembourg IBAN has 20 (LU28 0019 4006 4475 0000), and a Kuwaiti IBAN has 30 (KW81 CBKU 0000 0000 0000 1234 5601 01). A payment system that knows the country code therefore knows exactly how many characters to expect.

IBANs appear in two forms. The electronic form is one continuous string with no spaces, which is what payment systems process. The print form splits the string into groups of four for readability, as on bank statements and invoices. The spaces carry no meaning, and IBANs use only uppercase letters.

Worked Example: Reading and Validating an IBAN

The example IBAN used in ISO documentation is a hypothetical UK account:

GB82 WEST 1234 5698 7654 32

In the UK, the BBAN is the four-letter bank code, the six-digit sort code and the eight-digit account number, so every UK IBAN has 22 characters.

How the check digits work

The validation method is called MOD 97 (from ISO 7064). A bank or payment form checks an IBAN like this:

1. Move the first four characters to the end: WEST12345698765432GB82.
2. Convert letters to numbers, where A = 10, B = 11 and so on up to Z = 35. W becomes 32, E 14, S 28, T 29, G 16, B 11. The string becomes 3214282912345698765432161182.
3. Divide that number by 97. If the remainder is exactly 1, the IBAN passes.

Issuing a new IBAN uses the same formula in reverse: the bank temporarily sets the check digits to 00, runs the calculation, and subtracts the remainder from 98 to get the two check digits. This design catches any single mistyped character and any two adjacent characters typed in the wrong order. That is why an online banking form can reject a wrong IBAN instantly, before the payment is submitted.

How IBANs Are Used

You give your IBAN to anyone who needs to pay you by bank transfer, such as an employer abroad, a foreign customer or a relative sending money from Europe. When you send money to an account in an IBAN country, your bank asks for the recipient’s IBAN. The IBAN only routes funds into an account. It is not a card number or a password, and it cannot be used to withdraw cash.

Inside the Single Euro Payments Area (SEPA), the IBAN is the only account identifier required for euro credit transfers and direct debits. EU rules made the BIC optional for these payments, so a transfer from Spain to Germany typically needs only the beneficiary’s name and IBAN.

Outside IBAN countries, domestic transfers keep their own systems. A US account is identified by a routing (ABA) number plus an account number, and a Canadian account by institution, transit and account numbers. When a US or Canadian bank sends a wire to an IBAN country, it collects the recipient’s IBAN and usually the recipient bank’s SWIFT/BIC. For money coming the other way, the sender abroad needs the US or Canadian account details and SWIFT code, because no US or Canadian IBAN exists. A website that generates a “US IBAN” is not producing a real identifier.

How to find your IBAN

If your account is in an IBAN country, look in these places:

• Your bank statement, usually printed near the account number.
• Your online or mobile banking app, often under account details or “receive money.”
• Your bank directly, by branch, phone or secure message.

Many online banks and other fintech providers also issue IBANs. The country code at the start shows which country’s banking system the account belongs to, which can affect which payment schemes and protections apply.

IBAN vs. SWIFT/BIC vs. Account Number

IBAN vs. account number. An IBAN contains your account number but is not the same thing: in the UK example, the account number 98765432 is only one part of the IBAN. Entering only the account number into an IBAN field will fail validation.

IBAN vs. SWIFT/BIC. SWIFT (the Society for Worldwide Interbank Financial Telecommunication) runs the messaging network that banks use to send payment instructions to each other, and it predates IBAN. The BIC (Bank Identifier Code), commonly called the SWIFT code, tells the network which bank receives the message; the IBAN tells that bank which account to credit. “SWIFT code” and “BIC” refer to the same identifier. SWIFT also acts as the registration authority that maintains the official IBAN Registry of country formats.

Why IBAN Was Created

Before IBAN, each country formatted bank, branch, routing and account codes in its own way. Cross-border payments regularly arrived with information misread or missing, which led to rejected transfers, delays and extra bank charges for investigation and repair. IBAN gave every account a format that any bank could parse and check automatically. The standard developed in stages:

• 1997: ISO published ISO 13616:1997, the first IBAN standard.
• Shortly after: the European Committee for Banking Standards (ECBS) issued a stricter version that allowed only uppercase letters and required a fixed IBAN length for each country.
• 2003: ISO 13616:2003 replaced the earlier versions.
• 2007: ISO 13616-1:2007 specified that IBAN elements should support international data processing, without dictating how banks store the data internally.

IBAN began as a European tool for electronic payments between banks. It has since spread to parts of the Middle East, Africa and Latin America, as the Kuwaiti example above shows.

Limitations of IBAN

• A valid IBAN is not a verified recipient. The check digits confirm that the number is internally consistent, not that the account exists, is open, or belongs to the person you intend to pay. A fraudster’s IBAN on a fake invoice passes the same check. Confirm payment details through a channel you already trust before a first payment.
• It does not cover every country. The US, Canada, Australia and most of Asia do not use IBAN domestically.
• It does not set costs or speed. Fees, exchange rates and delivery times depend on the banks, payment schemes and any intermediary banks involved, not on the IBAN.
• It can change. If a bank merges, restructures its codes, or you move your account, your IBAN may change even when you keep the same bank relationship.

FAQs

The Bottom Line

Anyone sending or receiving money across borders, especially to or within Europe, needs to know their IBAN and where to find it. For SEPA euro transfers, the recipient's name and IBAN are usually enough. A valid IBAN only proves the number is well formed, so confirm payment details through a trusted channel before paying someone new.