How to Read an IBAN: Country Code, Check Digits, and BBAN Explained

An IBAN (International Bank Account Number) looks like a random string of letters and digits — but every character has a precise meaning. Once you know the four sections that make up any IBAN, you can decode any account number in the world in seconds. This guide walks through each section with real examples from the United Kingdom and Germany.

The Four Parts of an IBAN

Every IBAN — regardless of country — follows the same structural template. It always starts with two letters and two digits, followed by a country-specific block called the BBAN.

Here is the full UK IBAN used in most documentation examples: GB29 NWBK 6016 1331 9268 19

• GB — Country code
• 29 — Check digits
• NWBK — Bank identifier (NatWest)
• 60 16 13 31 92 68 19 — Sort code + account number

And a German example: DE89 3704 0044 0532 0130 00

• DE — Country code
• 89 — Check digits
• 3704 0044 — Bankleitzahl (bank routing number)
• 0532 0130 00 — Account number

Part 1: The Country Code

The first two letters of any IBAN are the ISO 3166-1 alpha-2 country code. This tells payment systems which country's rules to apply when interpreting the rest of the number. Every country has a unique two-letter code — DE for Germany, GB for the United Kingdom, FR for France, AE for the United Arab Emirates.

The country code determines the expected total length of the IBAN. A German IBAN is always 22 characters. A UK IBAN is always 22 characters. A French IBAN is always 27 characters. Any IBAN with the wrong length for its country code is invalid before you even look at the other digits.

As of 2026, 84 countries have assigned IBAN country codes under the ISO 13616 standard. You can verify the expected format for any country on the ibanchecker.cash IBAN formats page.

Part 2: The Check Digits

Characters three and four are always two decimal digits — never letters — calculated using the MOD-97 algorithm defined in ISO 13616. Their sole purpose is error detection: if you mistype a single character anywhere in the IBAN, the check digits will almost certainly not match the result of recalculating MOD-97 over the corrected number.

The check digits are calculated at account creation time and encoded into the IBAN permanently. They do not change. When a bank or payment system receives an IBAN, one of the first things it does is recompute the expected check digits and compare them against positions three and four. A mismatch means the IBAN was either transcribed incorrectly or is outright fabricated.

Statistically, the MOD-97 check catches 98% of single-digit errors and 100% of adjacent digit transpositions — the two most common mistakes when copying account numbers by hand.

The check digits 89 in DE89... and 29 in GB29... are valid outputs of MOD-97 for those specific account identifiers. Change any digit in either IBAN and the check will fail.

Part 3: The Bank Identifier (Within the BBAN)

After the check digits comes the BBAN — Basic Bank Account Number. This is the country-specific portion of the IBAN. Its structure, length, and meaning are defined separately by each country's banking authority.

The BBAN almost always begins with a bank or branch identifier:

• Germany: the first 8 digits of the BBAN are the Bankleitzahl (BLZ) — the German bank routing code. In DE89 3704 0044 ..., the BLZ is 37040044, which identifies Deutsche Bank in Cologne.
• United Kingdom: the first 4 characters of the UK BBAN are a letter-based bank code (NWBK for NatWest), followed by a 6-digit sort code (601613) that identifies the specific branch.
• France: the BBAN starts with a 5-digit bank code, then a 5-digit branch code, before the account number itself.

The bank identifier portion is what allows payment processors to route a transfer to the correct financial institution. Without it, they would have no way to know which bank holds the account.

Part 4: The Account Number

The final section of the BBAN is the actual account number — the digits that identify a specific customer account at that bank. This is the same account number you would use for domestic transfers within the country.

In DE89 3704 0044 0532013000, the account number is 0532013000 — a 10-digit number at Deutsche Bank Cologne.

In GB29 NWBK 6016 1331926819, the account number is 31926819 — the 8-digit UK account number at NatWest branch 601613.

The IBAN wraps this account number in an internationally-understood package. The domestic account number alone is meaningless outside its country — the IBAN adds the routing context needed to deliver it correctly across borders.

Why Spaces Don't Count

IBANs are often written with spaces every four characters for readability — this is called the print format. When transmitting electronically, spaces are removed, producing the electronic format. Both represent the same number.

GB29 NWBK 6016 1331 9268 19 (print) and GB29NWBK60161331926819 (electronic) are identical. Payment systems always strip spaces before processing. If you are building software that handles IBANs, normalize to the electronic format before validation.

How to Validate an IBAN You've Been Given

Reading an IBAN tells you what each section means. Validating one tells you whether it is actually correct. A complete IBAN validation checks:

• The country code is a recognized IBAN country
• The total length matches the expected length for that country
• The character types are correct (letters where expected, digits where expected)
• The check digits pass the MOD-97 calculation

Before making any international payment, paste the IBAN into the ibanchecker.cash validator. It runs all four checks instantly, identifies the bank and BIC code where available, and flags any structural problems before you authorize the transfer.

Last updated: June 2026