Updated October 18, 2026. Quick answer: Lines 1b, 2 and 3 carry the short-term totals from Form 8949, one line for each pair of boxes you checked there. You finish Form 8949 first, then copy its totals across, and figure column (h) as proceeds minus cost plus any adjustments. The numbers come from your Form 8949, not from the Form 1099-B directly.
Read box by box from the IRS form text: Form 1099-CAP boxes 1 to 5.
What lines 1b, 2 and 3 ask for
The form captions the three lines by the box checked on Form 8949. Line 1b reads “Totals for all transactions reported on Form(s) 8949 with Box A or Box G checked”, line 2 reads “Totals for all transactions reported on Form(s) 8949 with Box B or Box H checked” and line 3 reads “Totals for all transactions reported on Form(s) 8949 with Box C or Box I checked”. The form’s heading tells you where the transactions are listed: “Use Form 8949 to list your transactions for lines 1b, 2, 3, 8b, 9, and 10.” They sit in Part I of Schedule D (Form 1040), the short-term part. The meaning of each box is on the Form 8949 boxes A to L guide.
Do Form 8949 first
The instructions put the order plainly: “Complete Form 8949 before you complete line 1b, 2, 3, 8b, 9, or 10 of Schedule D.” They describe what the form is for: “Use Form 8949 to report the sale or exchange of a capital asset (defined later) not reported on another form or schedule”. The line-by-line mechanics of that form are on the Form 8949 page. A sale reported on a Form 1099-B shows proceeds and basis in the boxes covered at 1099-B box 1d and 1e.
If you chose the shortcut on Schedule D line 1a, those sales stay off Form 8949 and are not repeated here.
Where the number comes from: column (h)
For these lines the instructions say “Figure gain or loss on each line. First, subtract the cost or other basis in column (e) from the proceeds (sales price) in column (d). Then combine the result with any adjustments in column (g). Enter the gain or loss in column (h). Enter negative amounts in parentheses.” They give three short examples. “Column (d) is $6,000 and column (e) is $2,000. Enter $4,000 in column (h).” For a loss: “Column (d) is $6,000 and column (e) is $8,000. Enter ($2,000) in column (h).” And with an adjustment in column (g): “Column (d) is $6,000, column (e) is $2,000, and column (g) is ($1,000).” These examples are the IRS’s own and apply to lines 1b, 2, 3, 8b, 9 and 10.
Special case: a loss that is not deductible
Some transactions need a particular box. The instructions say “Report a transaction that results in a nondeductible loss in Part I or Part II of Form 8949 (depending on how long you held the property).” “Unless you received a Form 1099-B or Form 1099-DA for the sale or exchange, check box C or box I at the top of Part I” for a short-term holding. The adjustment is entered in column (g) of Form 8949, and the Form 8949 code W page covers the wash sale version of an adjustment.
Where it goes next
Lines 1b, 2 and 3 are added into the Part I total, captioned “Net short-term capital gain or (loss). Combine lines 1a through 6 in column (h).” The other Part I lines are at Schedule D lines 4 and 5 and Schedule D lines 6 and 7.
Edition and line numbers
This page reads the 2025 Schedule D (Form 1040) and its 2025 instructions, the current files irs.gov served on 2026-10-18. They are byte-identical to the archived copies and they are the files for the tax year 2025 return, filed in 2026. The schedule says “Attach to Form 1040, 1040-SR, or 1040-NR.” Schedule D has its own instructions booklet, titled “Instructions for Schedule D (Form 1040)”. Check the tax year printed on the schedule you are filling in and use the line numbers on that year’s schedule, because a different year’s schedule can number or word its lines differently.
Common mistakes
- Filling in lines 1b, 2 or 3 before Form 8949 is done. The instructions say “Complete Form 8949 before you complete line 1b, 2, 3, 8b, 9, or 10 of Schedule D.”
- Leaving out column (g) adjustments. The instructions say to “combine the result with any adjustments in column (g).”
- Entering a loss without parentheses. The instructions say “Enter negative amounts in parentheses.”
Related: Schedule D (Form 1040), Form 8949, Form 8949 boxes A to L, 1099-B box 1d and 1e, and Form 8949 code W.
Sources
- Instructions for Schedule D (Form 1040), Capital Gains and Losses (2025): https://www.irs.gov/pub/irs-pdf/i1040sd.pdf
- Schedule D (Form 1040), Capital Gains and Losses (2025): https://www.irs.gov/pub/irs-pdf/f1040sd.pdf
Read from the IRS documents linked above on October 18, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.