How it works
Form 8949 lists each capital asset sale with the description, dates acquired and sold, proceeds, cost basis, adjustments, and gain or loss. Transactions are grouped by holding period and by whether a broker reported them with basis, without basis, or not at all, using the checkboxes at the top of each part. Totals flow to Schedule D.
Why it matters
The checkbox categories are how the IRS reconciles your return against Forms 1099-B and 1099-DA. An active trader may have thousands of lines; the IRS accepts summary totals with an attached statement, but the detail must exist and match.
Example
A trader with 3,000 crypto transactions attaches a reconciled transaction report to Form 8949, reports one summary line per checkbox category, and keeps the wallet-level records that support it.
Related: Schedule D, Form 1099-DA.
