Money & WorkHow it works
How an IBAN catches a typo before money moves.
Digits three and four of an IBAN are check digits. To verify, the IBAN is rearranged, letters become numbers and the huge result is divided by 97. Only if the remainder is 1 is the IBAN formally valid. A single typo or transposed digits is guaranteed to be caught. It only checks the format, not whether the account actually exists.
Useful: If your banking app rejects an IBAN, you've almost certainly mistyped; don't just try the next number that passes.
Source: de.wikipedia.org