Credit card check digit calculator

Client

The credit card check digit is the final Luhn mod-10 symbol. When OCR or manual entry misreads one digit, the prefix may still be correct. This page shows pass/fail and whether the checksum matches the other digits.

Using the calculator

Paste or type digits only. On pass, the full string satisfies Luhn mod-10. On fail, one transposed digit is the usual cause—compare against a known test PAN from your processor docs.

Sensitive data: checks run only in your browser. Prefer processor-published test card numbers, never live PANs on shared devices.
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Spaces and dashes are stripped before counting digits and running Luhn. Card-network labels come from common public BIN/IIN ranges—they may mismatch exotic co-branded or new ranges.

16 digits after cleanup

Likely network: Visa

Luhn checksum: passes — algorithm-only; does not mean the card is active or genuine.

Common use cases

  • Fix one wrong trailing digit without re-scanning a test document.
  • Document expected check digit behavior in QA specs for checkout forms.

Common mistakes to avoid

  • Calculating check digit on partial PAN strings

    Run Luhn on the full digit sequence including the check position.

FAQ

How is the credit card check digit calculated?

Luhn mod-10: double alternate digits from the right, sum, remainder mod 10—the check digit makes the total divisible by 10.

Which digit is the check digit?

The rightmost digit in the primary account number for Luhn validation.

Common search terms

Phrases people search for that match this tool. See the full long-tail keyword index.

  • credit card luhn check online
  • visa mastercard bin checker browser
  • payment card checksum validator no upload
  • validate primary account number luhn locally
  • discover amex prefix checker heuristic online

More tools

Related utilities you can open in another tab—mostly client-side.