International Bank Account Number - Features

Features

One of the design aims of the IBAN was to enable as much validation as possible to be done at the point of data entry. In particular, the computer program that accepts an IBAN will be able to validate:

• the country code
• the number of characters in the IBAN correspond to the number specified for the country code
• the BBAN format specified for the country code
• the account number, bank code and country code combination is compatible with the check digits.

The check digits are calculated using MOD-97-10 as per ISO/IEC 7064:2003 (abbreviated to mod-97 in this article) which specifies a set of check character systems capable of protecting strings against errors which occur when people copy or key data. In particular, the standard states that the following can be detected:

• "all single substitution errors (the substitution of a single character for another, for example 4234 for 1234);"
• "all or nearly all single (local) transposition errors (the transposition of two single characters, either adjacent or with one character between them, for example 12354 or 12543 for 12345);" Since the IBAN error detection uses mod-97, it will trap all such errors.
• "all or nearly all shift errors (shifts of the whole string to the left or right);" These errors will be trapped by the computer program as they will result in an incorrect format.
• "a high proportion of double substitution errors (two separate single substitution errors in the same string, for example 7234587 for 1234567);"
• "a high proportion of all other errors."

The underlying rules for IBANs is that the account-servicing financial institution should issue an IBAN, as there are a number of areas where different IBANs could be generated from the same account and branch numbers that would satisfy the generic IBAN validation rules. In particular cases where 00 is a valid check digit, 97 will not be a valid check digit, likewise if 01 is a valid check digit, 98 will not be a valid check digit, similarly with 02 and 99.

The UN CEFACT TBG5 has published a free IBAN validation service in 32 languages for all 57 countries that have adopted the IBAN standard. They have also published the Javascript source code of the verification algorithm.

A similar English language IBAN checker which is restricted to ECBS member country bank accounts is available on their website.