General Banking
Validation Checksum
A validation checksum is a value derived from a number's digits using a mathematical algorithm. It provides a built-in error-detection mechanism that can catch typos, transpositions, and other common mistakes before a payment is submitted.
Different bank number formats use different checksum algorithms. IBANs use the MOD-97 algorithm defined in ISO 7064, which produces two check digits that catch over 99% of transcription errors. US routing numbers use a weighted sum algorithm where each digit is multiplied by 3, 7, or 1 in a repeating cycle, and the total must be divisible by 10. Some national account number formats include their own check digits calculated with country-specific algorithms.
Checksums are the first line of defense against payment errors. A single mistyped digit will almost always cause a checksum failure, alerting the sender before money is sent to the wrong account. Validating checksums client-side — as BankCheck does — gives instant feedback without exposing account details to a server.
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