Updated October 18, 2026. Quick answer: Lines 1a to 6 are the income section of the S corporation’s page 1. Line 1a is gross receipts or sales, line 1b takes out returns and allowances, line 2 is cost of goods sold from Form 1125-A, line 4 is the Form 4797 gain or loss, line 5 is other income, and line 6 adds up the result. The receipts come from the corporation’s books; the other lines come from attached forms and statements.
What goes on line 1a
The instructions say: “Enter on line 1a gross receipts or sales from all business operations except for amounts that must be reported on lines 4 and 5.” They add “If a cost offset method under section 451(b) or (c) is elected, the resulting gross income is reported on line 1a.” The form’s caption for the line is “Gross receipts or sales”. This page is part of the Form 1120-S line-by-line walk-through, and the deduction lines that follow are on the lines 7 to 12 page.
What stays out of the income lines
The instructions open the income section with a caution: “Report only trade or business activity income on lines 1a through 5.” They continue “Don’t report rental activity income or portfolio income on these lines.” On tax-exempt income they say “Don’t include any tax-exempt income on lines 1a through 5.” The form carries the same limit in a caution above the income lines: “Include only trade or business income and expenses on lines 1a through 22.” A sole proprietor meets the same sorting question on Schedule C lines 2 to 5.
Timing of receipts
On timing, the instructions say “In general, advance payments are reported in the year of receipt.” For the exceptions for corporations that use an accrual method of accounting, and for installment sale rules that also affect line 1a, read the full text of the line 1a instructions.
Lines 1b and 1c: returns and allowances, then the balance
The instructions for line 1b say “Enter cash and credit refunds the corporation made to customers for returned merchandise, rebates, and other allowances made on gross receipts or sales.” Line 1c is the balance column on the form and has no instruction paragraph of its own (checked by searching both text extractions for the heading), so the printed layout is what the form gives you: 1a, less 1b, leaves 1c. As a computed illustration, not an IRS example, gross receipts of $250,000 less returns and allowances of $10,000 leave a balance of $240,000.
Line 2: cost of goods sold
The form’s caption is “Cost of goods sold (attach Form 1125-A)”. The instructions say “Complete and attach Form 1125-A, Cost of Goods Sold, if applicable.” They continue “Enter on line 2 the amount from Form 1125-A, line 8.” The cost figure is therefore built on Form 1125-A first, and line 2 only receives the result.
Line 3: gross profit
The caption reads “Gross profit. Subtract line 2 from line 1c”. The instructions have no separate paragraph for line 3 (checked in both extractions), so the caption is the whole rule. Continuing the computed illustration, not an IRS example, a balance of $240,000 less cost of goods sold of $90,000 gives a line 3 gross profit of $150,000.
Line 4: net gain or loss from Form 4797
The caption is “Net gain (loss) from Form 4797, Part II, line 17 (attach Form 4797)”. The instructions open with a caution: “Include only ordinary gains or losses from the sale, exchange, or involuntary conversion of assets used in a trade or business activity.” For the form itself, see Form 4797. Part II of that form is explained at Form 4797 lines 10 to 12.
Line 5: other income or loss
The caption is “Other income (loss)”. The instructions say “Enter any other trade or business income (loss) not included on lines 1a through 4.” They add “List the type and amount of income on an attached statement.” The examples include “Interest income derived in the ordinary course of the corporation’s trade or business, such as interest charged on receivable balances.” and “Taxable income from insurance proceeds.” The paragraph ends with “Don’t include items requiring separate computations by shareholders that must be reported on Schedules K and K-1.”
A separate instruction covers ordinary income from a partnership, estate or trust: “Enter the ordinary income (loss) shown on Schedule K-1 (Form 1065) or Schedule K-1 (Form 1041) or other ordinary income (loss) from a foreign partnership, estate, or trust.” It adds “If the amount entered is from more than one source, identify the amount from each source.” And “Don’t include portfolio income or rental activity income (loss) from a partnership, estate, or trust on this line.” The instructions list further examples of other income that are not reproduced here.
Line 6: total income
The caption is “Total income (loss). Add lines 3 through 5”. The instructions have no separate paragraph for line 6 (checked in both extractions), so the caption is the rule. As a computed illustration, not an IRS example, a line 3 gross profit of $150,000 plus a line 5 other income of $5,000, with nothing on line 4, combines to $155,000.
Where the number comes from
Line 1a comes from the corporation’s own books and sales records for the tax year. Line 1b comes from its records of refunds and allowances. Line 2 comes from Form 1125-A, line 8. Line 4 comes from the attached Form 4797, and line 5 from the statement attached to the return. Owners who also file a sole proprietor schedule can compare the layout with Schedule C, where the same receipts-to-gross-profit sequence appears for a single owner.
Where it goes next
Line 6 is the figure the deductions are taken from. The caption for line 22 is “Ordinary business income (loss). Subtract line 21 from line 6”. The deduction lines begin on the lines 7 to 12 page, and line 22 is covered on the lines 13 to 22 page. Income that must be stated separately goes to Schedule K, which begins on the Schedule K lines 1 to 4 page.
Edition and line numbers
This page reads the 2025 Form 1120-S 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 title line reads “U.S. Income Tax Return for an S Corporation” and the period line reads “For calendar year 2025 or tax year beginning”. 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
- Putting rental or portfolio income on the income lines. The instructions say “Don’t report rental activity income or portfolio income on these lines.”
- Leaving tax-exempt income in the income lines. The instructions say “Don’t include any tax-exempt income on lines 1a through 5.”
- Typing a cost of goods sold figure on line 2 without the form behind it. The instructions say “Complete and attach Form 1125-A, Cost of Goods Sold, if applicable.”
Related: Form 1120-S, Schedule C lines 2 to 5, Schedule C, Form 4797, and Form 4797 lines 10 to 12.
Sources
- Instructions for Form 1120-S, U.S. Income Tax Return for an S Corporation (2025): https://www.irs.gov/pub/irs-pdf/i1120s.pdf
- Form 1120-S, U.S. Income Tax Return for an S Corporation (2025): https://www.irs.gov/pub/irs-pdf/f1120s.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.