CUSIP Validator (Securities Identifier Check)

It checks the structure and checksum: that the code is 9 characters from the set 0-9, A-Z and the symbols asterisk, at-sign and hash, and that the final check digit matches the standard mod-10 calculation. A valid result means the code is well-formed, not that a security with that CUSIP is currently listed.

Each of the first eight characters is converted to a value: digits are themselves, A to Z are 10 to 35, and the symbols asterisk, at-sign and hash are 36, 37 and 38. Every second value counting from the left is doubled, then each value contributes the sum of its two digits. The totals are summed and the check digit is ten minus the last digit of that sum, modulo ten.

A CUSIP is a nine-character identifier used mainly for US and Canadian securities. An ISIN is a twelve-character global identifier that, for those securities, is built by adding a two-letter country prefix in front of the CUSIP and a separate check digit at the end. So a US ISIN usually contains its CUSIP in the middle.

Usually a single character is mistyped, which breaks the mod-10 checksum. Other causes are the wrong length or a character outside the allowed set. The validator shows the computed check digit so you can compare it with the one you entered.

No. All validation runs locally in your browser using client-side JavaScript. The CUSIP you enter is never uploaded, logged, or stored, so it never leaves your device.