What is the IBAN check digit algorithm?

IBAN check digits use the MOD-97-10 algorithm defined in ISO 7064. The algorithm moves the first 4 characters to the end of the IBAN, replaces each letter with its numeric equivalent (A=10 through Z=35), then verifies the resulting integer modulo 97 equals 1.

Why do IBANs have check digits?

Check digits let any software or person detect typing errors or transpositions in an IBAN before submitting a payment. A single character error almost always produces a different MOD-97 result, catching the mistake before money is sent.

Can I verify an IBAN checksum manually?

Yes. Step-by-step: (1) Move the first 4 characters to the end. (2) Replace each letter with its number (A=10, B=11 … Z=35). (3) Divide the resulting integer by 97. If the remainder is 1, the IBAN checksum is valid.

Does a valid checksum mean the account exists?

No. A valid MOD-97 checksum confirms the IBAN is formatted correctly but does not verify the account exists or belongs to a specific person. Only the recipient's bank can confirm account existence.

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.

IBAN

Sending money to another country?

Wise shows the exchange rate and its fee before you send.

Send with Wise

Partner link. If you open a Wise account through it and send money between two currencies, Wise pays ibanchecker.cash a commission; what you pay does not change. How this works

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

Rearrange: Move the first four characters (country code + check digits) to the end of the string. For DE89370400440532013000, this produces 370400440532013000DE89.
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.
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.
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