Last updated: April 2026 · Reviewed by Alex Morgan, CFP

IBAN Validator — Check Any European Bank Account Number

An IBAN (International Bank Account Number) is the standardised format used across Europe and beyond to identify bank accounts for international wire transfers. Even a single digit error can send your payment to the wrong account or cause it to be rejected. This validator checks your IBAN against the ISO 13616 standard using the MOD-97 algorithm — the same mathematical check used by banks — and extracts the country code, check digits, bank identifier, and account number. Enter your IBAN below to validate it instantly. No data is transmitted to any server; all processing runs in your browser.

This calculator provides estimates for informational purposes only and does not constitute financial advice. Consult a qualified financial advisor for decisions based on your individual circumstances.

What Is an IBAN?

The International Bank Account Number (IBAN) is a standardised numbering system developed by the International Organisation for Standardisation (ISO) and the European Committee for Banking Standards (ECBS) to uniquely identify bank accounts across national borders. The standard is defined in ISO 13616.

Before the IBAN was introduced, cross-border payments relied on ad-hoc domestic account number formats, which led to frequent errors and high failure rates for international transfers. The SEPA (Single Euro Payments Area) mandate, introduced in 2007 and fully enforced by 2014, made IBAN mandatory for all euro-area payments. Today more than 80 countries have adopted the IBAN standard, although the United States, Canada, Australia, and most of Asia still use domestic formats.

An IBAN can be up to 34 characters long, though actual lengths are fixed per country. It consists entirely of alphanumeric characters (letters A-Z and digits 0-9) with no special characters. When written for human reading it is conventionally split into groups of four characters separated by spaces, but the spaces are not part of the IBAN itself and are stripped before any processing.

IBAN Structure

Every IBAN follows a three-part structure:

[CC][KK][BBAN]

CC   = 2-letter ISO 3166-1 country code  (e.g. GB, DE, FR)
KK   = 2-digit check digits              (e.g. 82 in GB82)
BBAN = Basic Bank Account Number         (remaining chars, country-specific length)

Example: GB82 WEST 1234 5698 7654 32
  CC   = GB  (United Kingdom)
  KK   = 82  (check digits)
  BBAN = WEST12345698765432
         ^^^^               bank sort code prefix (4 chars for UK)
             ^^^^^^^^^^^^^^  branch + account number

The BBAN encodes the domestic account number in a country-specific format. For a UK IBAN, the BBAN contains the 4-character bank code (e.g., WEST for Westpac/Western Bank), followed by the 6-digit sort code and 8-digit account number. For a German IBAN the BBAN is purely numeric: an 8-digit bank code (Bankleitzahl) followed by a 10-digit account number. Each country's IBAN registry specifies the exact BBAN structure.

The MOD-97 Check Digit Algorithm

The two check digits at positions 3-4 of every IBAN are calculated using a modulo-97 algorithm. The MOD-97 algorithm was chosen because 97 is a prime number and provides excellent coverage of common transcription errors — it catches all single-digit errors, all transpositions of adjacent characters, and most other error patterns.

The validation algorithm works in four steps:

1. Rearrange: Move the first four characters (country code + check digits) to the end of the string.
2. Convert letters to numbers: Replace each letter with its numeric equivalent: A=10, B=11, C=12, ..., Z=35. This converts the entire IBAN into a long sequence of digits.
3. Compute modulo 97: Treat the resulting digit string as one very large integer and calculate its remainder when divided by 97.
4. Check the result: If the remainder equals 1, the IBAN is structurally valid. Any other result means the IBAN contains an error.

Because JavaScript's Number type loses precision for very large integers, this validator uses a chunked iterative method — processing the digit string in 9-character blocks — to compute the modulo exactly without floating-point errors.

Worked Example: Validating GB82 WEST 1234 5698 7654 32

Let's trace through the complete MOD-97 validation of the IBAN GB82WEST12345698765432:

Step 1 — Strip spaces, uppercase:
  GB82WEST12345698765432

Step 2 — Check country code and length:
  Country: GB (United Kingdom), expected length = 22 ✓
  Actual length: 22 ✓

Step 3 — Rearrange: move first 4 chars (GB82) to end:
  WEST12345698765432GB82

Step 4 — Replace letters with numbers (A=10, ..., Z=35):
  W=32, E=14, S=28, T=29, G=16, B=11
  → 3214282912345698765432161182

Step 5 — Compute 3214282912345698765432161182 mod 97:
  Process in chunks of 9 digits:
  321428291 mod 97 = 76
  762345698 mod 97 = 14   (prepend remainder 76)
  14765432  mod 97 = 29   (prepend remainder 14)
  29161182  mod 97 = 1    (prepend remainder 29)

Step 6 — Result = 1 ✓  →  IBAN is VALID

The check digit value of 82 in "GB82" was chosen precisely so that the final MOD-97 result equals 1. When an IBAN is issued by a bank, the check digits are calculated by temporarily setting them to "00", running the algorithm, and then setting KK = 98 - (result mod 97).

Country-Specific IBAN Lengths

The table below lists the IBAN length for every country this validator supports. Lengths are defined in the SWIFT IBAN Registry, which is updated periodically as new countries adopt the standard.

Common Mistakes When Using IBANs

Confusing IBAN with SWIFT/BIC. These serve different purposes. The IBAN identifies the account; the SWIFT/BIC identifies the bank. For most SEPA payments inside Europe, the IBAN alone is sufficient. For intercontinental payments — for example, sending euros from the US to Germany — you typically need both the recipient's IBAN and their bank's SWIFT/BIC code.

Using domestic formats for international payments. If you are in the UK and want to pay a German supplier, you must use their German IBAN (starting with DE) — not their local account number. Some UK businesses still quote their sort code and account number on invoices. To construct the IBAN, use your bank's online tool or a trusted IBAN calculator that knows the German BBAN structure.

Assuming MOD-97 = guaranteed correct. A valid MOD-97 result means the IBAN is structurally correct. It does not prove the account exists, that it is active, or that it belongs to the person you intend to pay. For high-value transfers, always confirm the IBAN verbally or via a separate communication channel — email can be intercepted and IBAN details changed by fraudsters in business email compromise (BEC) attacks.

Entering IBANs manually from handwritten sources. The characters most commonly confused are: 0 (zero) vs O (letter O), 1 (one) vs I (letter I) vs l (lowercase L), and 8 vs B. The MOD-97 check will catch most such errors, but double-checking against the source document is always recommended for large payments.

Privacy Note

This IBAN validator runs entirely in your browser using client-side JavaScript. The IBAN you enter is never transmitted to our servers, not stored in any database, and not shared with any third party. You can verify this by inspecting the browser's network tab while using the validator — no network requests are made when you type. The source code for the validation logic is the standard ISO 13616 MOD-97 algorithm implemented in TypeScript.

Frequently Asked Questions