Glossary
Check Digit
Position 9 of a VIN. A single character (0-9 or X) computed from the other 16 to detect typos or forgery.
Standard: ISO 3779
Definition
The check digit is a single character at position 9 of a VIN. It is computed by assigning each other character a numeric value (letters map to specific digits — A=1, B=2, etc., excluding I, O, and Q), multiplying each by a position weight (8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2), summing the products, and taking the remainder modulo 11. If the remainder is 10, the check digit is the letter X; otherwise it is the digit 0-9. Check digits are mandatory on VINs sold in North America and optional elsewhere — most European-market VINs include them anyway. A failed check digit usually means a typo, but can also indicate VIN cloning or a forged document.
Why it matters when buying a used car
A check-digit failure is the cheapest fraud catch there is. Before paying for a history report, run the free decode — if the check digit fails, you are looking at a typo or a fake VIN, and there is no point going further until that is resolved.
Use this on Carlytics
Often confused with
VIN
A VIN is the 17-character serial number that uniquely identifies a road vehicle worldwide, standardised by ISO 3779.
VDS
Positions 4 through 9 of a VIN. The VDS encodes model, body style, restraint system, engine, and the check digit.
VIN cloning
Stamping the VIN of a legitimate vehicle onto a stolen or written-off vehicle to give it a clean apparent identity.