The basic idea
IBAN checksum validation rearranges the IBAN, converts letters to numbers, and checks the result with a MOD-97 calculation. If the remainder matches the expected rule, the checksum passes.
What checksum catches
Checksum rules catch many common typing errors, transpositions, and malformed values. They cannot confirm account status, ownership, balance, payment eligibility, or official records.
Common mistakes
Do not collect unnecessary real account data just to test a checksum. Use examples or masked values where possible.
FAQ
Can a fake IBAN pass checksum?
Yes. A number can be structurally valid but not connected to a real account.
Is checksum validation useful?
Yes, for pre-checks and typo reduction, as long as its limits are clear.