IBAN validator & calculator
Instantly check whether an IBAN is correct, or work out the two check digits of a Spanish IBAN from the account's 20 digits. Everything is verified in your browser, without sending the number to any server.
You can type it with or without spaces. Works with IBANs from any country.
What an IBAN is and how it's built
The IBAN (International Bank Account Number) is the international format for a bank account number, used across Europe and beyond. A Spanish IBAN has 24 characters: it starts with ES (the country code), followed by two check digits and then the 20 digits of the traditional account number (bank, branch, internal check digits and account). Those two digits right after the "ES" are the key to validation.
How it's validated: the remainder after 97
The IBAN carries a built-in mathematical check to catch typing errors. The procedure, set out in an international standard, moves the first four characters to the end, turns the letters into numbers (A is 10, B is 11, up to Z, which is 35) and works out the remainder of dividing that very large number by 97. If the IBAN is correct, the remainder is always 1. Change a single digit and the remainder stops being 1, so the system catches most slips.
Valid format isn't the same as an account that exists
This distinction is worth keeping clear. A mathematically valid IBAN means it's well formed and there's no obvious transcription error, but it doesn't guarantee the account actually exists or belongs to who you think. That needs a bank check. This tool tells you whether the number is internally consistent, which is exactly what you want before setting up a direct debit or passing an IBAN to a client and risking a return over one mistyped digit.