IBAN Checksum Verifier

Enter any IBAN to see the MOD-97 check digit algorithm run step by step. Understand exactly why an IBAN passes or fails the ISO 13616 standard.

What Is the MOD-97 Algorithm?

Every IBAN includes two check digits at positions 3 and 4. These are computed using the ISO 7064 MOD-97-10 algorithm, also used by IBAN's governing standard ISO 13616. The algorithm can detect any single-digit error and most transposition errors, making it a reliable first-pass guard against typos.

The Four Steps Explained

1. Rearrange: Move the first four characters (country code + check digits) to the end of the string. For DE89370400440532013000, this produces 370400440532013000DE89.
2. Convert letters: Replace each letter with its numeric equivalent (A=10, B=11, …, Z=35). The country code letters become numbers, turning the string into a long integer. D becomes 13, E becomes 14, so DE89 at the end becomes 13148 9.
3. MOD 97: Compute the remainder when the numeric string is divided by 97. Because the number can be hundreds of digits long, this is done digit-by-digit to avoid integer overflow.
4. Validate: A remainder of 1 means the IBAN is structurally correct. Any other remainder means at least one character is wrong.

What MOD-97 Does Not Guarantee

A passing checksum confirms the IBAN is structurally valid — not that the account exists or is open. To verify that an IBAN maps to a real account at a real bank, use the full IBAN checker which also returns the bank name, BIC code, and SEPA reachability.

There is also a small statistical chance (~1-in-97) that a randomly corrupted IBAN still passes MOD-97. For financial transactions, always confirm the account details directly with the payee.

Last updated: June 2026