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CUSIP / ISIN Validator

Finance & Global IDs

Validate a CUSIP (9-char US security ID) or ISIN (12-char global security ID) using their official checksum algorithms. Free, in-browser, no data uploaded.

Reviewed by the thecalcu.com team · Last updated July 24, 2026

What is a CUSIP/ISIN?

The CUSIP / ISIN Validator checks whether a security identifier is structurally valid using each format's official checksum algorithm. Enter 9 characters for a CUSIP or 12 characters for an ISIN, the validator auto-detects the type and applies the correct algorithm.

CUSIP (9 characters): the standard US and Canadian security identifier, managed by CUSIP Global Services under the American Bankers Association. Used on all US exchange-listed equities, corporate bonds, government bonds, mutual funds, and ETFs. The check digit uses a modified doubling algorithm with alphanumeric transliteration.

ISIN (12 characters): the global security identifier under ISO 6166, consisting of a 2-letter country code + 9-character national security ID + 1 Luhn check digit. US ISINs embed the CUSIP in positions 3–11. Indian ISINs use country code "IN" and are assigned by NSDL.

The validator performs three checks:

  1. Length detection, 9 chars triggers CUSIP path; 12 chars triggers ISIN path
  2. Character validation, CUSIP: digits, uppercase letters, *, @, #; ISIN: 2 letters then alphanumeric
  3. Checksum, CUSIP modified doubling algorithm; ISIN Luhn on letter-expanded string

What it does not check: Whether the identifier is listed in the official CUSIP Global Services database, currently tradeable, or associated with an active issuer. For official lookup, use CUSIP Global Services, the SEC's EDGAR database, or the NSE/BSE website for Indian ISINs.

Related tools: SWIFT / BIC Validator for bank identifier codes and IBAN Validator for bank account numbers.

All validation is client-side. No data is transmitted.

Why Use a CUSIP / ISIN Validator?

Securities operations teams, fintech developers, and financial data engineers work with CUSIP and ISIN identifiers in trade booking systems, portfolio management platforms, regulatory reporting (SEC filings, RBI reporting), and data reconciliation workflows. A transposed digit in a CUSIP or ISIN causes trade booking failures, reporting errors, and reconciliation breaks.

Fintech developer use case: An Indian fintech company building a US equity trading platform receives security identifiers from a market data feed and validates each CUSIP before storing in the securities master database. Checksum validation filters out data feed errors (corrupted characters, truncated identifiers) before they propagate into downstream systems.

Fund operations use case: A mutual fund operations team reconciling portfolios between the fund administrator and the custodian finds ISIN mismatches. The validator identifies which ISINs have structural errors (checksum failures) versus potential correct-but-mismatched ISINs that need manual review.

Who Should Use This Validator?

Financial technology developers building US equity, bond, or fund platforms that process CUSIP and ISIN identifiers in trade booking, settlement, or reporting systems.

Indian asset management and fund operations teams that work with global securities (using ISINs) and US domestic securities (using CUSIPs) in cross-border portfolio management.

Compliance and regulatory reporting teams submitting SEC filings, SEBI disclosures, or FPI holding reports that require valid security identifiers.

Quantitative analysts and financial data engineers building securities master databases or reconciliation workflows that need identifier integrity validation.

What Insights Does the CUSIP / ISIN Validator Give You?

For CUSIP: the issuer code (positions 1–6), issue code (positions 7–8), and check digit (position 9). The issuer code identifies the company that issued the security; the issue code differentiates multiple securities from the same issuer (common stock, preferred stock, different bond series).

For ISIN: the country code (ISO 3166-1 alpha-2, positions 1–2), the national security identifier (positions 3–11, which is the CUSIP for US securities), and the Luhn check digit (position 12). The country code immediately identifies the security's country of registration.

How to use this CUSIP/ISIN calculator

  1. Enter the identifier, 9 characters for CUSIP, 12 for ISIN.
  2. Check the Valid/Invalid badge, auto-detection and checksum run instantly.
  3. Read the details, issuer code, issue code or country code, and check digit.
  4. For US ISINs: the CUSIP is embedded in positions 3–11.
  5. For official lookup: query CUSIP Global Services, SEC EDGAR, or NSE/BSE for listed securities.
  6. Related tools: use the SWIFT / BIC Validator for bank identifiers.
Show formula & methodology ↓Show less ↑

Formula & Methodology

CUSIP check digit:
For positions 1–8 (0-indexed: 0–7):   value = transliterate(char)  // A=10..Z=35, *=36, @=37, #=38, 0-9=face value   if position is even (0,2,4,6): use value as-is   if position is odd (1,3,5,7): double value; if result ≥ 10, add digits sum all 8 results check digit = (10 - (sum % 10)) % 10

ISIN Luhn check digit:
Expand each character: letters → two-digit number (A=10..Z=35), digits → single digit Concatenate expanded string Apply standard Luhn: valid if sum % 10 === 0

Valid and invalid examples:

| Identifier | Valid? | Type | Note |
|---|---|---|---|
| 037833100 | ✓ | CUSIP | Apple Inc. |
| US0378331005 | ✓ | ISIN | Apple Inc. US ISIN |
| INE002A01018 | ✓ | ISIN | Reliance Industries (IN) |
| 037833101 | ✗ | CUSIP | Check digit should be 0 |
| US037833100 | ✗ | N/A | 11 chars, neither CUSIP nor ISIN |

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Frequently Asked Questions

What is a CUSIP?
A CUSIP (Committee on Uniform Security Identification Procedures) is a 9-character alphanumeric identifier assigned to US and Canadian securities, including stocks, bonds, and mutual funds. CUSIPs were introduced in 1968 and are administered by the American Bankers Association (ABA) in partnership with S&P Global. The first 6 characters identify the issuer, the next 2 identify the specific issue, and the 9th character is a check digit calculated from the first 8.
What is an ISIN?
An ISIN (International Securities Identification Number) is a 12-character alphanumeric identifier that provides a globally unique code for any security, stocks, bonds, derivatives, and other instruments. Defined by ISO 6166, an ISIN consists of a 2-character ISO country code, a 9-character national security identifier (for US securities, this is the CUSIP), and a single Luhn check digit. ISINs are the global standard used by exchanges, clearing houses, and financial regulators worldwide.
What is the difference between CUSIP and ISIN?
CUSIP is the US/Canada standard (9 characters) while ISIN is the global standard (12 characters). US securities have both, the ISIN for a US stock is built by prepending 'US' to the 9-character CUSIP and appending a new Luhn check digit. For example, Apple Inc. has CUSIP 037833100 and ISIN US0378331005. Institutional investors working with US exchanges use CUSIPs; global cross-border transactions use ISINs.
How does the CUSIP checksum work?
The CUSIP checksum uses a modified doubling algorithm. For each of the first 8 characters, letters are converted to numbers (A=10, B=11, ..., Z=35; *=36, @=37, #=38), digits keep their value. Characters at even positions (2nd, 4th, 6th, 8th) are doubled, if the doubled value is a two-digit number, its digits are summed. All 8 resulting values are summed, and the check digit is (10 - (sum mod 10)) mod 10.
How does the ISIN checksum work?
The ISIN uses the standard Luhn algorithm, but applied to a string derived by expanding all letters to their numeric equivalents (A=10, B=11, ..., Z=35). For example, 'US' becomes '3028', making the 12-character ISIN expand to a longer digit string. The Luhn algorithm is then applied to this expanded string, doubling every second digit from the right, subtracting 9 if the result exceeds 9, then summing. A valid ISIN produces a sum divisible by 10.
Does this validator confirm the security is currently listed or tradeable?
No, the validator checks checksum integrity only. A passing checksum confirms the identifier was correctly constructed, but it does not confirm the security is currently listed on any exchange, that the issuer is still active, or that the CUSIP/ISIN is in the official CUSIP Global Services or ISIN database. Securities can be valid CUSIP/ISIN format but delisted, matured (for bonds), or cancelled.
What securities use CUSIP and ISIN identifiers?
CUSIPs and ISINs are used for equities (stocks), corporate bonds, government bonds, municipal bonds, mutual funds, ETFs, options, futures, and other tradeable securities. Every US-listed security has a CUSIP; every security traded internationally has or can have an ISIN. Indian securities listed on NSE and BSE have ISINs with the country code 'IN', for example, Reliance Industries has ISIN INE002A01018.
Is my CUSIP/ISIN data stored when I validate it?
No, all validation runs entirely in your browser. The CUSIP or ISIN is never sent to any server, stored, or logged. Security identifiers are public data (they appear in regulatory filings and exchange data), but we keep validation fully client-side. The tool works offline once loaded.
What is the ISIN for Indian blue-chip stocks?
Some well-known Indian securities ISINs: Reliance Industries, INE002A01018; HDFC Bank, INE040A01034; Infosys, INE009A01021; TCS, INE467B01029. All start with 'IN' (the ISO country code for India). To look up any NSE/BSE-listed security's ISIN, search the NSE or BSE website by company name or symbol.
How do I use the CUSIP / ISIN Validator?
Enter the identifier in the input field, 9 characters for CUSIP, 12 characters for ISIN (hyphens and spaces are stripped automatically). The validator auto-detects whether it is a CUSIP or ISIN based on the length and runs the appropriate checksum. The Valid/Invalid badge updates instantly. The details panel shows the issuer code, issue code, and check digit breakdown for CUSIP; the country code, national ID, and check digit for ISIN.
What is the relationship between CUSIP and SEDOL?
SEDOL (Stock Exchange Daily Official List) is the 7-character security identifier used on the London Stock Exchange. It is separate from and not compatible with CUSIP. ISINs for UK securities use SEDOL as the national security ID (with 'GB' country code). CUSIPs are specific to North America (US and Canada); SEDOLs to the UK and Ireland; ISINs are the global wrapper that includes both regional identifiers.
Also known as
CUSIP validatorISIN validatorsecurities identifier checkvalidate CUSIPvalidate ISIN