Check Digit Verification (CDV) is a mathematical validation method applied to South African bank account numbers to confirm they are structurally valid before submission to PayInc (BankservAfrica) for EFT processing. South African banks use proprietary check-digit algorithms — each bank has its own variant — that verify the relationship between the digits in an account number and a check digit embedded in the number. CDV catches typos, transposed digits, and invented account numbers instantly, without any bank inquiry. It is the first line of defence in a two-layer account verification strategy: CDV first (instant, offline), then AVS (live bank-to-bank inquiry) for identity and account ownership confirmation.

Each South African bank uses its own proprietary check-digit algorithm for validating account numbers. CDV libraries for the South African market include algorithms for all major banks: Absa, FNB, Nedbank, Standard Bank, Capitec, TymeBank, African Bank, Mercantile, and others. The algorithm takes the account number and applies a mathematical formula — typically involving weighted digit sums modulo a prime number — to produce an expected check digit. If the check digit in the account number matches the expected value, the number passes CDV. If not, it is structurally invalid. Branch codes (universal branch codes in modern SA banking: 051001 for Standard Bank, 250655 for FNB, etc.) are also validated as part of the CDV process.

No — CDV validates account number format only. It cannot confirm that the account belongs to a specific person, is active, or is not fraudulently submitted. CDV will pass a structurally valid account number even if it belongs to someone else or is a closed account. AVS (Account Verification Service) is required to confirm account ownership, identity matching, and account status. The correct sequence is always: CDV first (instant format check), then AVS (live bank-to-bank identity verification). CDV is free or near-free per check; AVS has a cost per inquiry. Running CDV first eliminates structurally invalid accounts before they consume AVS inquiry budget.

Most South African payment service providers (PSPs), banks' business banking portals, and EFT collection platforms include CDV as a built-in validation step when account details are entered. However, if you are building a custom integration or capturing banking details through your own web or mobile forms before passing them to a PSP, you should implement CDV at the point of capture to give immediate user feedback on invalid account numbers. Open-source CDV libraries for South African banks are available for Java, .NET, Python, PHP, and JavaScript/TypeScript on platforms such as GitHub. CDV validation at capture time significantly reduces data quality issues downstream.