IBAN Validation: How International Bank Account Numbers Work

IBAN (International Bank Account Number) is a standardized system for identifying bank accounts across national borders. Proper IBAN validation prevents costly payment errors and rejected transactions.

IBAN Structure

An IBAN consists of up to 34 alphanumeric characters:

Part	Length	Description
Country code	2 letters	ISO 3166-1 alpha-2 (e.g., TR, DE, GB)
Check digits	2 digits	Calculated using MOD-97
BBAN	Up to 30	Basic Bank Account Number (country-specific)

IBAN Length by Country

Country	Length	Example Format
Turkey (TR)	26	TR00 0000 0000 0000 0000 0000 00
Germany (DE)	22	DE00 0000 0000 0000 0000 00
United Kingdom (GB)	22	GB00 AAAA 0000 0000 0000 00
France (FR)	27	FR00 0000 0000 0000 0000 0000 000
Netherlands (NL)	18	NL00 AAAA 0000 0000 00

MOD-97 Validation Algorithm

Move the first 4 characters to the end

Convert letters to numbers (A=10, B=11, ... Z=35)

Compute the remainder when divided by 97

If the remainder is 1, the IBAN is valid

Common IBAN Errors

Typos: A single wrong digit invalidates the entire IBAN

Wrong length: Each country has a fixed IBAN length

Missing country code: Always include the 2-letter prefix

Spaces vs. no spaces: Both formats are valid; remove spaces for processing

Developer Best Practices

Strip all whitespace before validation

Validate both format and check digits

Display IBANs in groups of 4 characters for readability

Store IBANs without spaces in databases

Try It Yourself

Validate any IBAN number instantly with our free IBAN Validator. Check the format, country, and MOD-97 check digits in real time.