CUSIP checksum checker

Client

Reference-data spreadsheets and trade-support tickets often paste CUSIP symbols beside ISIN or SEDOL columns. This page strips separators, confirms the nine-character layout, and recomputes the published mod‑10 check—pair it with ISIN validate when the same instrument also carries a twelve-character ISO wrapper.

What this checks

CUSIP uses nine characters: issuer and issue body plus a mod‑10 check digit. Even positions are doubled on single-digit mapped values (0–35), products are digit-summed, and the ninth character completes the chain—arithmetic only, not a vendor master lookup.

How to use

Paste the nine-character symbol after removing spaces. Pair with ISIN validate when the row also includes a twelve-character ISO wrapper.

For UK seven-character symbols, use SEDOL checker (weights 1, 3, 1, 7, 3, 9—not CUSIP doubling).

Privacy: checksum math runs locally in your tab. Toolcore does not query CUSIP Global Services, issuer registries, or market data—format and check digit only.
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After cleanup the identifier is 9 characters: six issuer, two issue, one decimal check. Letters map to values 10–35 (A=10 … Z=35). Even positions (2nd, 4th, 6th, 8th) are doubled and digit-summed before the mod‑10 chain—distinct from ISO 6166 ISIN expansion.

Result

US ISINs often embed the same nine-character body inside a twelve-character ISO wrapper—open ISIN validate when you need country prefix and Luhn expansion instead.

Passes CUSIP mod‑10 check for 037833100.

Issuer (6)
037833
Issue (2)
10

Nearby workflows on Toolcore

  • ISIN validate — after the CUSIP body passes—expand letters for ISO Luhn when needed.
  • SEDOL checker — for London-listed symbols in the same reference extract.
  • Payment card checker — when the column is a card PAN (different mod‑10 chain than CUSIP bodies).

Common use cases

  • Sanity-check a CUSIP copied from a Bloomberg export before loading it into an internal security master.
  • Explain why a nine-character North American symbol fails checksum while the related ISIN still passes ISO Luhn expansion.
  • Spot typos in issuer/issue segments during onboarding when only the CUSIP column is available in legacy CSV feeds.
  • Contrast CUSIP doubling rules with GS1 modulus-10 on retail GTINs when adjacent teams mix supply-chain and capital-markets identifiers.

Common mistakes to avoid

  • Treating a passing check as proof of listing or eligibility

    Checksum validation confirms arithmetic only—not trading status, corporate actions, or regulatory approvals.

  • Applying ISIN letter expansion to CUSIP bodies

    CUSIP doubles even positions on single-digit character values; ISIN expands letters to two digits before a different Luhn chain.

  • Expecting CUSIP Global Services metadata

    Issuer names, issue descriptions, and maturity data require licensed vendor feeds—this page performs local format math only.

FAQ

Does Toolcore query CUSIP Global Services?

No—the check digit and layout rules run entirely in your browser tab.

How does the check digit work?

Map each of the first eight characters to 0–35 (digits stay, A=10 through Z=35). Double values at even positions (2nd, 4th, 6th, 8th), sum digits of each product, add everything, then take (10 − sum mod 10) mod 10 as the ninth character.

What about CINS or private placements?

This page expects standard nine-character CUSIP layout with a decimal check digit—the same mod-10 chain used for common equity and debt symbols in North American reference files.

Common search terms

Phrases people search for that match this tool. See the full long-tail keyword index.

  • cusip checker online check digit
  • validate cusip checksum in browser
  • north american securities identifier mod 10
  • cusip validate no registry lookup

More tools

Related utilities you can open in another tab—mostly client-side.