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ISIN Validator

Check whether a security's ISIN is valid.

How it is calculated

An ISIN has 12 characters: a two-letter country code, a nine-character alphanumeric identifier and a final check digit. The tool first checks this layout (the check digit must be a number). Then each letter is replaced by two digits, A = 10 … Z = 35. The final digit is removed, and the Luhn algorithm is applied to the rest from right to left: double every second digit starting with the rightmost, subtract 9 from any result above 9, and add all digits. The expected check digit is (10 − sum mod 10) mod 10.

Lower-case letters and spaces at the ends are accepted. A "Valid" status means only that the check digit fits, so a typing error is unlikely; it does not prove that the security exists or who issues it.

Worked example

Take US0378331005. Letters become digits: U = 30 and S = 28, so the first eleven characters give 3028037833100. Doubling every second digit from the right and adding gives a sum of 45. The expected check digit is (10 − 5) mod 10 = 5. The last character of the code is 5, so the tool shows the status Valid with check digit 5.

Try this example →

Common mistakes

  • Treating "Valid" as proof that the security exists; only the arithmetic is checked.
  • Typing the letter O instead of the digit 0, or I instead of 1.
  • Adding spaces or hyphens inside the code: only the 12 characters are accepted, and a malformed code gives no result.
  • Confusing ISIN with a ticker symbol or a CUSIP; they have different lengths and are issued separately.

About this calculator

This tool validates a 12-character ISIN (International Securities Identification Number), the global standard (ISO 6166) for uniquely identifying a specific securities issue — stocks, bonds, and other instruments. An ISIN consists of a 2-letter country code, a 9-character alphanumeric national security identifier, and a single check digit computed with a variant of the Luhn algorithm after converting letters to numbers.

Custodians, brokers, exchanges, and back-office settlement systems use ISIN validation to catch typos before trades are booked, since a single wrong character can route an order to the wrong security.

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Comments (1)

  • Editorial team

    For US securities, the nine characters after the country code are the CUSIP: in US0378331005 that is 037833100, followed by the check digit 5. A Valid status only shows the check digit fits, not that the security exists or is the one you meant, so confirm the issuer and instrument name with your broker or a registry. If a real code is reported as invalid, post it and say where you copied it from.

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