How to Read a Business Tax Return: Deductions, Schedules, and Red Flags

Reading a business tax return means working from the top of the form down: identify the entity, follow revenue into gross profit, subtract the deductions, land on taxable income, and then check the reconciliation and balance sheet to see whether the numbers hold together. Every business return follows that same logic. The line numbers move around depending on which form the company filed, but the flow is consistent, and once you know where to look, you can tell within a few minutes whether a business is profitable, how it spends its money, and whether anything on the page deserves a second look.

Start by Identifying the Form

The form itself tells you the entity type and how profits get taxed, so this is always the first step.

Sole proprietors report business income on Schedule C, filed as part of their personal Form 1040.¹
Partnerships file Form 1065, an information return showing how profits and losses split among the partners.²
C-corporations file Form 1120.
S-corporations file Form 1120-S.³

The distinction matters for how you read the rest of the return. C-corporations pay tax at the entity level, so the tax due sits on the return itself. Partnerships and S-corporations pass income through to their owners’ personal returns, so the return you’re holding may show no tax owed even though real tax gets paid downstream on the K-1s.

At the top of every form you’ll find the company’s legal name, mailing address, and Employer Identification Number. The EIN is a nine-digit number that works like a Social Security number for the business. Confirm the name and EIN match what you expect. Mismatches are one of the fastest ways for returns to get flagged.

Revenue, Cost of Goods Sold, and Gross Profit

Gross receipts or sales appear on Line 1a of both Form 1120 and Form 1065. This is the total money collected from customers before anything is subtracted.⁴ Line 1b captures returns and allowances (refunds, rebates, similar adjustments), and Line 1c shows the net figure after those come out. To gauge the raw scale of a business, start at Line 1a.

Next comes gross profit. Subtract cost of goods sold from net receipts to get there. COGS appears on Line 2, and the underlying calculation is on Form 1125-A, attached to both Form 1120 and Form 1065.⁴ Form 1125-A breaks down beginning inventory, materials purchased during the year, and labor directly tied to producing goods. Gross profit lands on Line 3 and tells you how much the business earned from its core operations before overhead, salaries, and other operating costs come into play.

Working Through the Deductions

The deduction section is where you see how the business spends its money. On Form 1120, deductions run from Line 12 through Line 26, totaling on Line 27. On Form 1120-S, the range is Lines 7 through 20, totaling on Line 21.⁵ The categories are similar across forms, but line numbers shift, so pay attention to which form you’re reading.

A handful of lines deserve close attention.

Officer compensation and employee wages are broken out separately on Form 1120 and 1120-S. Officer compensation sits on Line 12 of Form 1120 and Line 7 of Form 1120-S, apart from general salaries and wages on Line 13 and Line 8 respectively. If officer pay looks disproportionately high or low for the size of the business, that’s worth investigating. An S-corporation owner who takes large distributions but reports minimal salary is one of the more common patterns the IRS targets.

Rent appears on Line 16 of Form 1120, Line 11 of Form 1120-S, and Line 13 of Form 1065.²

Repairs and maintenance (Line 14 on Form 1120, Line 9 on Form 1120-S) covers costs to keep existing assets in working condition. Improvements that extend an asset’s life or increase its value don’t belong here; they belong in depreciation.

Business meals are deductible at 50% of the actual cost, provided the meal is directly related to business activity. Entertainment expenses (sporting event tickets, rounds of golf) aren’t deductible at all. When food and drinks are served during an entertainment event, those costs are deductible only if they’re itemized separately on the receipt. Meal expenses are usually bundled into “Other Deductions” (Line 26 on Form 1120, Line 20 on Form 1120-S), often with an attached statement breaking out the category.

Depreciation and Section 179

Depreciation is a non-cash deduction that spreads the cost of property and equipment over its useful life. It appears on Line 20 of Form 1120, Line 14 of Form 1120-S, and Line 16 of Form 1065.⁶ The detail flows from Form 4562, attached to the return. Because depreciation reduces taxable income without any cash going out the door, it often makes a business look less profitable on paper than it is in cash terms. Keep that in mind when you’re using a return to judge financial health.

Section 179 of the tax code lets businesses deduct the full purchase price of qualifying equipment in the year of purchase instead of spreading it out. If a Section 179 deduction is later disallowed during an audit for missing documentation or misallocated expenses, the business faces both the additional tax and an accuracy-related penalty of 20% on the underpayment.⁷

Finding Taxable Income and the Tax Owed

Once all deductions come out of total income, you land on the number the IRS actually taxes. On Form 1120, taxable income is Line 30, and the federal corporate rate is a flat 21%.⁴ The math is straightforward: multiply Line 30 by 0.21.

Pass-through returns work differently. On Form 1120-S, ordinary business income is on Line 22. On Form 1065, it appears on Line 23 of page 1.² Neither partnerships nor S-corporations pay federal income tax at the entity level. Each owner’s share flows to a Schedule K-1, which reports their portion of ordinary income, rental income, capital gains, and other items.⁸ Owners then report those amounts on their personal returns and pay tax at their individual rates. When you’re reading a partnership or S-corp return, the K-1s are where the real tax consequences land.

State corporate income tax is a separate layer that won’t appear on the federal return. Rates run from zero in states with no corporate income tax up to as high as 11.5%, with a typical rate around 6.5%. Factor that in if you’re using the return to think about total tax burden.

Book-to-Tax Reconciliation on Schedule M-1 or M-3

A company’s internal accounting profit and its taxable income rarely match. Schedule M-1 explains the gap. You’ll find it on page 4 or 5 of the return, and it walks through the specific items that create the difference between what the books show and what the tax return reports.⁴ Common adjustments include tax-exempt interest (income on the books but not on the return), non-deductible meals and entertainment, and depreciation methods that differ between financial reporting and tax rules.

If the corporation’s total assets are $10 million or more, it must file the more detailed Schedule M-3 instead.⁴ Schedule M-3 breaks the reconciliation into finer categories, making it harder to bury questionable adjustments. When you’re analyzing a return, the reconciliation schedule is where you catch discrepancies that the income and deduction sections alone won’t show.

Reading Schedule L: The Balance Sheet

Schedule L is a snapshot of everything the business owns and owes on the last day of the tax year. Assets come first: cash, accounts receivable, inventories, investments, and long-term property like buildings and equipment shown at historical cost minus accumulated depreciation. On Form 1065, total assets are on Line 14.⁹ Comparing total assets at the beginning and end of the year gives you a quick read on whether the business is growing, shrinking, or holding steady.

The bottom half covers liabilities and equity. Accounts payable, mortgages, and other debts show what the company owes outsiders. The equity section (shareholder equity on Form 1120-S, partner capital on Form 1065) shows what’s left for the owners after debts. A healthy balance sheet has equity growing over time, funded by retained earnings rather than by more debt.

Not every business has to complete Schedule L. Corporations with both total receipts and total assets under $250,000 can skip it by checking the appropriate box on Schedule K of Form 1120.⁴ Partnerships meeting similar conditions under Schedule B, question 4, are also exempt. If a return you’re reading skips Schedule L, check whether it legitimately qualified for the exemption before assuming something is missing.

Red Flags to Watch For While You Read

Some patterns invite IRS scrutiny. Knowing what an auditor looks for helps you read a return with the same eye.

Income that doesn’t match third-party records. The IRS cross-references reported income against 1099 forms filed by customers, payment processors, and other businesses. A gap between what a company reports and what its 1099s show is the most reliable audit trigger there is.
Suspiciously round numbers. Real business expenses end in odd cents. A return full of round figures like $5,000 or $10,000 suggests estimates rather than records, and IRS systems flag the pattern.
Repeated losses. If a business reports a net loss in three or more of the past five years, the IRS may reclassify it as a hobby, which eliminates the ability to deduct expenses against other income.
Low officer salary on an S-corp return. Large distributions paired with minimal salary is a well-known strategy for avoiding payroll taxes, and one the IRS actively targets.

Reading a return well is really the practice of running two passes: one from top to bottom to see the story the numbers tell, and one across the reconciliation and balance sheet to see whether that story is internally consistent. If both passes hold up, the return probably says what it appears to say. If they don’t, you know where to ask questions.

1
Internal Revenue Service. 2025 Instructions for Schedule C (Form 1040)
2
Internal Revenue Service. 2025 Instructions for Form 1065 – U.S. Return of Partnership Income
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Internal Revenue Service. About Form 1120-S, U.S. Income Tax Return for an S Corporation
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Internal Revenue Service. Instructions for Form 1120 (2025)
5
Internal Revenue Service. Form 1120-S (2025) U.S. Income Tax Return for an S Corporation
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Internal Revenue Service. 2025 Instructions for Form 1120
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Office of the Law Revision Counsel. 26 U.S. Code 6662 – Imposition of Accuracy-Related Penalty on Underpayments
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Internal Revenue Service. 2025 Partners Instructions for Schedule K-1 (Form 1065)
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Internal Revenue Service. Instructions for Form 1065 (2025)