Missing Cost Basis Document Checklist & Next-Step Decision Guide

Start by defining what is missing

Write down the security, approximate acquisition period, account or brokerage, and the exact field that is unclear. Separate a missing number from a missing source document, and record what you know without filling gaps with guesses.

This checklist helps organize evidence. It does not determine tax basis, tell you what to report, or establish that any particular document will be accepted for a tax purpose.

Records to look for

• Current and historical brokerage statements, including year-end statements
• Trade confirmations and purchase notices
• 1099-B and related tax forms
• Dividend or capital-gain reinvestment records
• Transfer, ACATS, and account-closing correspondence
• Corporate-action notices for splits, mergers, ticker changes, or reorganizations
• DRS or transfer-agent statements and registration advices, where relevant
• Prior tax workpapers or notes that identify a source, date, or lot
• Email, paper, or external-drive copies that have not yet been inventoried

Record what each document supports

• Document name, issuing firm, account identifier, and statement period
• Security name, ticker, quantity, transaction date, and transaction type shown
• Whether the document is original, a copy, or an export
• Which facts are confirmed, which are candidate facts, and which remain unknown
• Any period, account, or transfer gap between two documents
• The next record request needed to test or clarify the gap

Do not close the gap by assumption

A later statement may show a balance without showing how an older lot was acquired. A receiving brokerage statement may not contain every historical detail from the delivering firm. A tax form may be useful evidence without answering every question about an older or transferred position.

Keep unresolved items visible. If the result may affect a tax return, sale, estate, transfer, or other consequential decision, bring the source records and open questions to a qualified tax professional or the relevant financial institution.