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CUSIP Validator

Enter a 9-character CUSIP to check whether its check digit is valid.

Result

Valid
0
037 833 100

How it is calculated

The code is trimmed and upper-cased, then it must be exactly 9 characters from 0-9, A-Z, *, @ or #; anything else returns no result. Each of the first 8 characters gets a value: digits keep their value, letters A to Z become 10 to 35, and *, @, # become 36, 37, 38. Every second character (positions 2, 4, 6, 8) is doubled, and the digits of each resulting number are added up (16 counts as 1 + 6). Then check = (10 − (sum mod 10)) mod 10. The code is Valid only if the 9th character is a digit equal to that check digit. The tool tests the check digit only; it does not look the security up.

Worked example

Take 037833100. The first 8 characters are 0, 3, 7, 8, 3, 3, 1, 0. Doubling positions 2, 4, 6 and 8 gives 6, 16, 6 and 0, and 16 counts as 1 + 6 = 7. The sum is 0 + 6 + 7 + 7 + 3 + 6 + 1 + 0 = 30. The check digit is (10 − 0) mod 10 = 0, which matches the 9th character, so the result is Valid and the code is shown as 037 833 100.

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Common mistakes

  • Entering 8 characters (the issuer and issue part without the check digit) or 10 characters. The tool needs exactly 9 and returns nothing otherwise.
  • Confusing the letter O with the digit 0, or I with 1. Letters are worth 10 or more, so one swapped character changes the sum and usually the verdict.
  • Treating Valid as proof that the security exists. A correct check digit only shows the code is internally consistent; a different typo can still produce another well-formed code.
  • Pasting an ISIN or SEDOL. Those are 12 and 7 characters long and use different rules, so a CUSIP check does not apply to them.

About this calculator

A CUSIP (Committee on Uniform Securities Identification Procedures) number is a 9-character code that uniquely identifies a North American security — the first 8 characters identify the issuer and issue, and the 9th is a check digit computed with a Luhn-like modulus-10 algorithm that weights and sums the numeric value of each preceding character. This validator recomputes that check digit from the first 8 characters and compares it to the 9th to confirm whether the code is structurally valid.

CUSIP validation is used by banks, brokerages, clearinghouses, and financial data systems to catch typos or transcription errors before a trade, settlement, or portfolio record references the wrong security — a single mistyped character in a CUSIP can point to an entirely different stock or bond, making the check digit an essential safeguard in financial data processing.

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Comments (1)

  • Editorial team

    If you hold an ISIN for a US or Canadian security, you can validate its CUSIP here. The CUSIP sits in the middle: in US0378331005 it is 037833100, the characters after the two-letter country code and before the final ISIN check digit. Paste only those nine. Which other identifiers, such as ISIN or SEDOL, would you want checked?

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