Updated October 18, 2026. Quick answer: Line 1a is a total of the gross proceeds reported to you on Form 1099-S or Form 1099-B for sales you are including on line 2, 10 or 20. Lines 1b and 1c total the gain and the loss you are including because of partial dispositions of MACRS assets. These lines are reference totals; the sales themselves are reported in the Parts that follow.
What lines 1a to 1c ask for
The form’s captions read “Enter the gross proceeds from sales or exchanges reported to you for 2025 on Form(s) 1099-B or 1099-S (or substitute statement) that you are including on line 2, 10, or 20.” for line 1a, “Enter the total amount of gain that you are including on lines 2, 10, and 24 due to the partial dispositions of MACRS assets” for line 1b, and “Enter the total amount of loss that you are including on lines 2 and 10 due to the partial dispositions of MACRS assets” for line 1c. The instructions give each of these three lines its own short paragraph, covered below. This page is part of the Form 4797 walk-through.
Line 1a: real estate reported on Form 1099-S
The instructions begin “Enter on line 1a the total gross proceeds from:” and the first of two items is “Sales or exchanges of real estate reported to you for 2025 on Form(s) 1099-S (or substitute statement(s)) that you are including on line 2, 10, or 20”. So the figure on line 1a is the proceeds amount printed on the closing form, and only for a sale you are carrying to line 2, line 10 or line 20. How that form is laid out is explained at Form 1099-S.
Line 1a: securities reported on Form 1099-B
The second item is “Sales of securities or commodities reported to you for 2025 on Form(s) 1099-B (or substitute statement(s)) that you are including on line 10 because you are a trader with a marktomarket election under section 475(f) in effect for the tax year.” This item is limited to line 10 and to a trader with that election. A broker form for an ordinary investment sale is covered at 1099-B box 1d and 1e, and the capital asset forms are at Form 8949.
Lines 1b and 1c: partial dispositions of MACRS assets
The line 1b instruction says “Enter on line 1b the total amount of gain that you are including on lines 2, 10, and 24 due to the partial dispositions of MACRS assets.” The line 1c instruction says “Enter on line 1c the total amount of loss that you are including on lines 2 and 10 due to partial dispositions of MACRS assets.”
The general rule behind them reads “You may elect to recognize a partial disposition of a Modified Accelerated Cost Recovery System (MACRS) asset”. It also says “In some cases, however, you are required to report the gain or loss on the partial disposition of a MACRS asset”. The required cases include “Sale of a portion of a MACRS asset.”
Where the number comes from
Line 1a comes from the proceeds shown on the Form 1099-S or Form 1099-B you received, or on a substitute statement, for the sales you are including on the later lines. Lines 1b and 1c come from your own totals of the partial-disposition gain and loss you carried to lines 2, 10 and 24. Nothing on these three lines is figured on the lines themselves; they total amounts reported elsewhere on the form.
Where it goes next
The sales behind line 1a are reported on lines 2 to 6 in Part I, on lines 10 to 12 in Part II, or on lines 19 to 24 in Part III. The Part III proceeds line carries a pointer back here: “Gross sales price (Note: See line 1a before completing.)”. The trader rule that sends securities to line 10 is explained on the lines 10 to 12 page.
Edition and line numbers
This page reads the 2025 Form 4797, Sales of Business Property and its 2025 instructions, the current files irs.gov served on 2026-10-18. They are the files for the tax year 2025 return, filed in 2026. The form’s own header says “Attach to your tax return.” Check the tax year printed on the form you are filling in and use the line numbers on that year’s form, because a different year’s form can number or word its lines differently.
Common mistakes
- Totaling every sale on line 1a. The caption limits the amount to proceeds “that you are including on line 2, 10, or 20.”
- Putting ordinary brokerage sales on line 1a. The instructions count 1099-B proceeds only “because you are a trader with a marktomarket election under section 475(f)”.
- Leaving a partial disposition out of lines 1b and 1c. The instructions say “Enter on line 1c the total amount of loss that you are including on lines 2 and 10 due to partial dispositions of MACRS assets.”
Related: Form 4797, Form 1099-S, 1099-B box 1d and 1e, Form 8949, and Form 4797 lines 10 to 12.
Sources
- Instructions for Form 4797, Sales of Business Property (2025): https://www.irs.gov/pub/irs-pdf/i4797.pdf
- Form 4797, Sales of Business Property (2025): https://www.irs.gov/pub/irs-pdf/f4797.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.