Check Digit Validator

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IBAN check digit validator

Move the first 4 characters (country code + check digits) to the end, convert every letter to a number (A=10 ... Z=35), and require the resulting number mod 97 to equal 1. The total length is fixed per country — this tool refuses country codes it doesn't have a registered length for rather than guessing.

DE89370400440532013005 fails the IBAN checksum, and 3 different single-character fixes would each satisfy it — checksum arithmetic alone cannot narrow this down further.

3 equally valid single-character fixes — checksum arithmetic alone cannot narrow this down to one digit:

  • DE89370400340532013005 (substitution, change the character at position 11 from "4" to "3")
  • DE89370400440539013005 (substitution, change the character at position 16 from "2" to "9")
  • DE89370400440532013000 (substitution, change the character at position 22 from "5" to "0")

A passing checksum only proves the number is arithmetically self-consistent. It does not prove an IBAN names an open account, an ISBN is assigned to a real book, or a card is active, unstolen, or has funds. Those require asking the bank, the ISBN registry, or the card network.

Try it: a valid example · a broken example

curl 'https://check-digit.gumballtools.com/api/v1/run?input=DE89%203704%200044%200532%200130%2000&format=iban'