ISIN Validator & Check-Digit Calculator
Validate ISINs (International Securities Identification Numbers) and compute their check digit. An ISIN is a 12-character code — a 2-letter ISO country code, a 9-character alphanumeric national security identifier (NSIN), and a single check digit — that uniquely identifies a financial security worldwide. The check digit uses the Luhn algorithm run over the full code after each letter is expanded to its decimal value (A=10 … Z=35). Everything runs locally in your browser.
Validate an ISIN
Compute check digit
ISIN structure: positions 1–2 are an ISO 3166-1 alpha-2 country code (two uppercase letters; XS is used for international securities), positions 3–11 are the 9-character NSIN (letters and digits), and position 12 is the check digit. Validation: each letter is replaced by its ordinal value (A→10, B→11, … Z→35), written as two decimal digits; digits pass through unchanged. The Luhn mod-10 sum is then taken over that digit string — starting from the rightmost digit (the check digit itself, which is not doubled), every second digit is doubled and, if the result exceeds 9, its digits are summed (equivalently, subtract 9). The ISIN is valid when the total is a multiple of 10. To compute the check digit, a placeholder 0 is appended to the expanded prefix, the Luhn sum is taken, and the check digit is (10 − sum mod 10) mod 10. ISINs are case-insensitive on input (uppercased here). Pairs with the IBAN and Luhn validators. Everything runs locally — nothing leaves your browser.