Check Digit Verification of CAS Registry Numbers

A CAS Registry Number® includes up to 10 digits which are separated into 3 groups by hyphens. The first part of the number, starting from the left, has 2 to 7 digits; the second part has 2 digits. The final part consists of a single check digit.

The check digit is developed by following a standard calculation shown below. Use it to see if you have a valid CAS Registry Number.

CAS Registry Check Digit Algorithm