CUSIP Validator & Check-Digit Calculator
Validate CUSIPs (Committee on Uniform Securities Identification Procedures codes) and compute their check digit. A CUSIP is a 9-character alphanumeric code — an 8-character issuer / national security identifier and a single trailing check digit — that identifies US and Canadian securities. It uses digits 0–9, the letters A–Z (vowels included), and an extended * @ # set, with a Luhn-style weighted check-digit algorithm. Everything runs locally in your browser.
Validate a CUSIP
Compute check digit
CUSIP structure: positions 1–8 are the alphanumeric issuer / NSIN, position 9 is the check digit. Allowed characters in the first eight are 0–9, A–Z (vowels included), and the extended private-issue characters * (36), @ (37) and # (38); the check digit is always 0–9. Each character has a numeric value: a digit → itself; a letter → its position in the alphabet plus 9, giving A=10, B=11, … Z=35. The check digit is computed by multiplying the eight NSIN values by the alternating weights [1, 2, 1, 2, 1, 2, 1, 2] (leftmost is ×1), summing the decimal digits of each product, then taking (10 − sum mod 10) mod 10. Validation recomputes that digit and compares it to the 9th character. CUSIPs are case-insensitive on input (uppercased here). A US CUSIP is embedded (without the leading US) as the NSIN of the matching 12-character ISIN. Pairs with the SEDOL and ISIN validators. Everything runs locally — nothing leaves your browser.