IBAN & SEPA
IBAN Check Digits (MOD-97)
IBAN check digits are the two numeric characters in positions 3 and 4 of every IBAN, immediately after the country code. They serve as a built-in error detection mechanism, calculated using the MOD-97 algorithm. Their sole purpose is to catch transcription and transposition errors before a payment is submitted.
To compute the check digits, the country code and 00 are appended to the BBAN, all letters are converted to numbers (A=10, B=11, ... Z=35), and the resulting integer is divided by 97. The check digits equal 98 minus the remainder. When validating, the full IBAN is rearranged and the same modular arithmetic must yield a remainder of 1. This detects virtually all single-digit errors and most transpositions of adjacent characters.
Check digits catch over 99% of accidental errors before money is sent, saving businesses and individuals from failed transfers, return fees, and delayed payments. If you receive a payment instruction with an IBAN, running it through BankCheck's IBAN validator will instantly confirm whether the check digits are correct.
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