A Form 8949 attachment is a separate statement listing each capital asset sale in full detail so that only summary totals appear on Form 8949 itself. You use one whenever your transactions don’t qualify to go straight onto Schedule D, which in practice means any time you have adjustments to make, trades without a 1099-B, or simply too many transactions to type out row by row. The IRS calls this “Exception 2,” and it works for 15 trades or 15,000 as long as the statement mirrors the form’s columns and the numbers reconcile to what your broker reported.1Internal Revenue Service. Instructions for Form 8949 – Section: Exceptions to Reporting Each Transaction on a Separate Row
Do You Actually Need an Attachment?
Check first whether you can skip Form 8949 entirely. Under Exception 1, qualifying transactions go directly on Schedule D lines 1a or 8a with no form and no statement. Every one of these has to be true for the group of trades you want to report this way:1Internal Revenue Service. Instructions for Form 8949 – Section: Exceptions to Reporting Each Transaction on a Separate Row
- Your broker reported the cost basis to the IRS on Form 1099-B or Form 1099-DA.
- The form shows no adjustments.
- The “Ordinary” box on the 1099-B or 1099-DA is not checked.
- You don’t need to correct the basis, proceeds, or type of gain or loss.
- You aren’t deferring gain through a Qualified Opportunity Fund investment.
- The transactions don’t involve collectibles.
If any of those fails for even some of your trades, those trades need Form 8949, and that’s where the attachment comes in. Most active traders and anyone holding digital assets will have at least some transactions that don’t fit Exception 1.
What to Enter on Form 8949 When You Attach a Statement
On the physical Form 8949, for each box category that applies to your attached transactions, fill in a single summary row:1Internal Revenue Service. Instructions for Form 8949 – Section: Exceptions to Reporting Each Transaction on a Separate Row
- Column (a): the broker’s name followed by “see attached statement.”
- Columns (b) and (c): leave blank.
- Column (f): enter “M” for multiple transactions. If other adjustment codes apply to the group, list them too.
- Columns (d), (e), (g), and (h): enter the combined totals for proceeds, basis, adjustments, and gain or loss from the matching section of your statement.
If you have statements from more than one broker, give each broker its own summary row. Rolling multiple brokers into one line is one of the most common ways to generate an IRS notice, because the service can’t match your single combined number against the individual 1099-Bs it received.
Form 8949 now has twelve box categories rather than six. Part I (short-term) uses boxes A, B, C, G, H, and I; Part II (long-term) uses D, E, F, J, K, and L. The G-through-L boxes are specifically for digital asset transactions reported on the new Form 1099-DA.2Internal Revenue Service. Form 8949 (2025) The box you check for each summary row depends on whether a 1099-B or 1099-DA was issued and whether basis was reported to the IRS. Each checked box needs its own summary row on the form and its own subtotal section on your statement.
What the Attached Statement Must Contain
Your statement has to carry the same data fields as Form 8949 and follow a similar layout. For every transaction, include:1Internal Revenue Service. Instructions for Form 8949 – Section: Exceptions to Reporting Each Transaction on a Separate Row
- Description of property (for example, “100 sh XYZ Corp” or “2.5 BTC”)
- Date acquired
- Date sold or disposed of
- Proceeds
- Cost or other basis
- Adjustment code and amount, if any
- Gain or loss
Grouping and Format
The IRS doesn’t require a particular file format. A spreadsheet exported to PDF is the common choice. What matters is the grouping: all Box A trades together, all Box B trades together, and so on through the twelve categories, with its own subtotal block for proceeds, basis, adjustments, and gain or loss at the end of each group. Those subtotals are exactly what you’ll copy to the matching summary rows on Form 8949.
Don’t mix short-term with long-term, and don’t combine traditional 1099-B securities with 1099-DA digital assets in the same group. Each box category is its own bucket. The statement needs to be organized clearly enough that someone reviewing the return can trace any single transaction back to the correct summary line.
Reconciling to the 1099-B or 1099-DA
The IRS gets its own copy of every 1099-B, so the numbers on your statement either match the broker’s figures or carry an explanation for the difference.3Internal Revenue Service. About Form 1099-B, Proceeds from Broker and Barter Exchange Transactions If you change a basis your broker reported, the row needs both an adjustment code and the dollar amount of the change. Substituting a different basis with no code attached is likely to generate a notice.
Digital assets add their own reconciliation issue. Brokers began issuing Form 1099-DA for sales starting in 2025 to report gross proceeds, and cost basis reporting for covered digital asset securities begins with sales in 2026.4Internal Revenue Service. Instructions for Form 1099-DA (2025) If your exchange didn’t report basis, or if you moved tokens between wallets before selling, you have to calculate basis from your own records. Those trades belong in Box H or K when a 1099-DA was issued without basis, or Box I or L when no 1099-DA came at all.2Internal Revenue Service. Form 8949 (2025)
Adjustment Codes to Know
Every adjusted transaction on your statement needs a code in column (f) explaining why the numbers differ from what the broker reported. The ones that come up most often:5Internal Revenue Service. Instructions for Form 8949 – Sales and Other Dispositions of Capital Assets
- Code B: the cost basis shown on your 1099-B or 1099-DA is incorrect; enter the correction in column (g).
- Code W: the loss is disallowed under the wash sale rule; enter the disallowed portion as a positive adjustment in column (g).
- Code M: multiple transactions reported on one row, which is the code you use any time you attach a statement under Exception 2.
- Code E: selling expenses or transaction costs not already reflected on the 1099-B or 1099-DA.
- Code H: excludable gain from the sale of a main home.
- Code T: the type of gain or loss on the 1099-B or 1099-DA is wrong (for instance, flagged short-term when it should be long-term).
More than one code can apply to a single transaction. A wash sale that also has an incorrect basis would carry both “W” and “B” in column (f), with the two adjustments combined in column (g).
How to File the Attachment
The mechanics differ depending on whether you e-file or mail a paper return.
E-Filing
Most commercial tax software accepts the statement as a PDF upload that transmits with the electronic return. Individual PDFs need to stay under 60 MB, the total of all attachments on a return can’t exceed 1 GB, and files can’t be password-protected.6Internal Revenue Service. Recommended Names and Descriptions for PDF Files Attached to Modernized e-File (MeF) Business Submissions Give the file a descriptive name under 64 characters, such as “Form8949_Attachment_ShortTerm.”
There’s one hybrid path worth knowing. If you e-file the return but don’t transmit the per-transaction detail electronically, you have to print Form 8453 and mail it to the IRS along with the Form 8949 statement after your electronic return is accepted.7Internal Revenue Service. Instructions for Form 8949 – Section: E-file Most filers no longer need this route because software handles PDF uploads directly, but it remains available if your software can’t take a large attachment.
Paper Filing
Attach the statement physically behind Form 8949. Your name and taxpayer identification number must appear on every page.1Internal Revenue Service. Instructions for Form 8949 – Section: Exceptions to Reporting Each Transaction on a Separate Row Pages do separate during processing. A detached page without identifying information has no way back to your return.
One prohibition applies regardless of filing method: do not write “Available upon request” on Form 8949 in place of the actual transaction detail. The instructions specifically bar it.1Internal Revenue Service. Instructions for Form 8949 – Section: Exceptions to Reporting Each Transaction on a Separate Row
Keeping the Records
Hold on to the broker statements, the attachment you prepared, and a copy of the filed return for at least three years from the filing date. If you underreported gross income by more than 25%, the IRS has six years to assess additional tax, so six years is the safer floor for anyone with sizable capital gains.8Internal Revenue Service.