IBAN Validator: How to Verify International Bank Account Numbers

What Is an IBAN?

IBAN (International Bank Account Number) is a standardized international system for identifying bank accounts, developed by the European Committee for Banking Standards (ECBS) and adopted by ISO as ISO 13616. Originally created to simplify EU cross-border transfers, IBAN is now used by over 77 countries.

IBAN Structure

An IBAN consists of up to 34 alphanumeric characters:

[Country Code (2)] [Check Digits (2)] [Basic Bank Account Number (BBAN, up to 30 chars)]

Example — German IBAN:

DE89 3704 0044 0532 0130 00
DE   = Country code (Germany)
89   = Check digits (validates the IBAN)
3704 0044 0532 0130 00 = BBAN (national account number)

Example — UK IBAN:

GB29 NWBK 6016 1331 9268 19
GB   = Country code (United Kingdom)
29   = Check digits
NWBK = Sort code prefix / bank identifier
6016 13 = Sort code
31926819 = Account number

How IBAN Validation Works

The MOD-97-10 Algorithm

IBAN validation uses modulo-97 arithmetic:

1. Move the first four characters to the end: 3704 0044 0532 0130 00 DE89 becomes 3704004405320130 00 DE89
2. Replace letters with numbers: A=10, B=11, ..., Z=35. D=13, E=14 → 37040044053201300013148 9
3. Compute the number mod 97
4. If the result equals 1, the IBAN is valid

What Validation Proves

• The IBAN passes the check digit algorithm
• The country code is recognized
• The BBAN length matches the country's expected length

What validation does NOT prove:

• The account actually exists
• The account belongs to the named person
• The transfer will succeed

IBAN Country Formats

Each country has a specific BBAN format and total IBAN length:

IBAN vs. SWIFT/BIC

IBAN identifies the account; SWIFT/BIC identifies the bank:

BIC/SWIFT: NWBKGB2L
  NWBK = Bank code (NatWest)
  GB   = Country code
  2L   = Location code

International transfers typically require both:

• IBAN: Where the money goes (account)
• SWIFT/BIC: How to route it (bank)

SEPA Transfers

The Single Euro Payments Area (SEPA) covers 36 European countries. SEPA transfers:

• Use only IBAN (no SWIFT/BIC required within SEPA since 2016)
• Are processed within 1 business day (SEPA Credit Transfer)
• Include instant payments up to €100,000 (SEPA Instant)
• Are free or low-cost within the Eurozone

Common IBAN Errors

Wrong Check Digits

Manually typed IBANs often have transposition errors. The check digit catches most single-character errors.

Incorrect Length

A German IBAN must be exactly 22 characters. Extra or missing digits cause immediate validation failure.

Formatting Issues

IBANs are often displayed in groups of 4 for readability (DE89 3704 0044) but transmitted without spaces. Validation tools should accept both formats.

Using the IBAN Validator

Our tool:

1. Enter any IBAN — accepts spaces and uppercase/lowercase
2. Validates format — checks country code, length, and check digits
3. Parses structure — shows bank code, branch code, account number
4. Identifies country — full country name from ISO code
5. Explains errors — clear messages for invalid IBANs

Use it before processing international payments to catch data entry errors and prevent failed transfers.