Every US C corporation must file Internal Revenue Service (IRS) Form 1120 every year. The obligation stands even with zero income, zero employees, and zero activity. Miss the deadline and the late-filing penalty starts at 5% of unpaid tax per month.
This guide covers who files Form 1120, when it is due, how to complete it, its schedules and deductions, the penalties, and the foreign-ownership traps that catch international founders. It follows the 2025 IRS Instructions for Form 1120, the primary source for corporate income tax filing.
What is Form 1120 and who must file it?
Form 1120, the U.S. Corporation Income Tax Return, is the IRS form domestic C corporations use to report income, gains, losses, deductions, and credits and to figure corporate income tax. The IRS requires all domestic corporations to file it unless specifically exempt. LLCs that elect C corporation treatment on Form 8832 file it too. It is the corporate analog to an individual’s Form 1040.
Some corporations file a related variant instead of the standard Form 1120. The table below maps each form to its filer.
| Form | Who files it | Source |
|---|---|---|
| Form 1120 | Domestic C corporations | IRS Instructions for Form 1120 |
| Form 1120-S | S corporations (elected via Form 2553) | IRS Instructions for Form 1120 |
| Form 1120-F | Foreign corporations with US income | IRS Instructions for Form 1120 |
| Form 1120-H | Homeowners associations | IRS Instructions for Form 1120 |
| Form 1120-REIT | Real estate investment trusts (REITs) | IRS Instructions for Form 1120 |
| Form 1120-C | Cooperatives | IRS Instructions for Form 1120 |
| Form 1120-PC / 1120-L | Property-casualty and life insurance companies | IRS Instructions for Form 1120 |
When is Form 1120 due?
Form 1120 is due the 15th day of the 4th month after the corporation’s tax year-end. For calendar-year corporations that date is April 15, per the IRS Instructions for Form 1120. A due date on a weekend or legal holiday shifts to the next business day. This 4th-month rule replaced the old 3rd-month deadline for tax years beginning after December 31, 2015.
One exception remains. Corporations with a June 30 fiscal year-end file by the 15th day of the 3rd month, which is September 15, for tax years beginning before January 1, 2026, per IRS Publication 509. Form 7004 grants an automatic 6-month extension to file, and June 30 filers get 7 months during the transition. An extension of time to file is not an extension of time to pay.
| Filer type | Tax year-end | Return due | Extended due (Form 7004) | Source |
|---|---|---|---|---|
| Calendar-year C corporation | Dec. 31 | April 15 | October 15 | IRS Instructions for Form 1120 |
| Fiscal-year C corporation | Last day of chosen month | 15th day of 4th month after year-end | 6 months later | IRS Instructions for Form 1120 |
| June 30 fiscal-year C corporation (years beginning before Jan. 1, 2026) | June 30 | September 15 | 7 months later | IRS Publication 509 |
Do I need to file Form 1120 with no income?
Yes. A C corporation must file Form 1120 every year regardless of income or activity, per the IRS Instructions for Form 1120. Dormant companies, holding companies, and corporations in dissolution or bankruptcy still file. The obligation follows the entity’s existence and tax classification, not its revenue.
A corporation with no income files a nil return, also called a zero return. First-time filers and pre-revenue startups often miss this. The base late-filing penalty is calculated on tax due, so a zero-tax return may carry no percentage penalty. The real exposure sits in attached information returns. A foreign-owned corporation that skips Form 5472 faces a $25,000 penalty even with zero income.
How do you file Form 1120 step by step?
Filing Form 1120 follows one sequence: gather your records, complete the income lines (1 to 11), complete the deduction lines (12 to 29), compute tax and payments (lines 30 to 36), attach the required schedules and forms, and e-file by your deadline. Confirm your C corporation classification and tax year first. Foreign-owned corporations attach Form 5472 before filing.
How do you complete page 1 of Form 1120?
Page 1 works top to bottom in line groups. Report gross receipts or sales on line 1, subtract returns and cost of goods sold (COGS) from Form 1125-A, and add dividends, interest, rents, and gains to reach total income on line 11. Enter deductions on lines 12 to 29 to reach total deductions. Line 30 is taxable income. Schedule J computes the tax, which flows to line 31.
What goes in a Form 1120 filing checklist?
Assemble these items before you start:
- Employer Identification Number (EIN) and entity formation documents
- Prior-year Form 1120
- Profit-and-loss statement and balance sheet
- Depreciation schedule, filed on Form 4562
- Cost of goods sold records for Form 1125-A
- Officer compensation records, reported on Form 1125-E if receipts reach $500,000
- Records of dividends received and distributions paid
- Estimated tax payment records
- Foreign ownership and related-party transaction records for Form 5472
What are the Form 1120 schedules?
Form 1120 includes built-in schedules C, J, K, L, M-1, and M-2, each covering one reconciliation or computation. Corporations with total assets of $10 million or more file Schedule M-3 instead of M-1, per the IRS Instructions for Schedule M-3. Corporations with total receipts and total assets both under $250,000 can skip Schedules L, M-1, and M-2.
| Schedule | What it reports | Who completes it | Source |
|---|---|---|---|
| Schedule C | Dividends and the dividends-received deduction (DRD) | Corporations receiving dividends | IRS Instructions for Form 1120 |
| Schedule J | Tax computation, credits, and other taxes | All filers | IRS Instructions for Form 1120 |
| Schedule K | Other information, including accounting method and ownership | All filers | IRS Instructions for Form 1120 |
| Schedule L | Balance sheet per books | Corporations with receipts or assets of $250,000 or more | IRS Instructions for Form 1120 |
| Schedule M-1 | Book-to-tax income reconciliation | Corporations with receipts or assets of $250,000 or more | IRS Instructions for Form 1120 |
| Schedule M-2 | Analysis of unappropriated retained earnings | Corporations with receipts or assets of $250,000 or more | IRS Instructions for Form 1120 |
| Schedule M-3 | Detailed book-tax reconciliation | Corporations with total assets of $10 million or more (full completion at $50 million) | IRS Instructions for Schedule M-3 |
What is Schedule M-2 on Form 1120?
Schedule M-2 reconciles unappropriated retained earnings from the start of the year to the end. It begins with the opening retained earnings balance, adds net income per books, subtracts distributions and dividends paid to shareholders, and arrives at the ending balance. The IRS uses it to track how corporate earnings move each year.
How is corporate income tax computed on Form 1120?
Taxable income on line 30 is taxed at a flat 21% federal corporate rate, applied on Schedule J. The rate comes from 26 U.S.C. Section 11(b), as amended by the Tax Cuts and Jobs Act (TCJA). It applies to tax years beginning after December 31, 2017, replacing the prior graduated structure that topped out at 35%. Schedule J also handles credits, recapture, and other taxes.
What deductions can a C corporation claim on Form 1120?
Form 1120 lines 12 to 29 cover ordinary business deductions, from officer compensation to advertising. Each deduction has its own line and, in some cases, a limit or an attached form. The table below lists the main deduction lines from the IRS Instructions for Form 1120.
| Deduction | Line | Limit or attachment | Source |
|---|---|---|---|
| Compensation of officers | 12 | Form 1125-E if receipts reach $500,000 | IRS Instructions for Form 1120 |
| Salaries and wages | 13 | Reduced by employment credits | IRS Instructions for Form 1120 |
| Repairs and maintenance | 14 | n/a | IRS Instructions for Form 1120 |
| Bad debts | 15 | n/a | IRS Instructions for Form 1120 |
| Rents | 16 | n/a | IRS Instructions for Form 1120 |
| Taxes and licenses | 17 | n/a | IRS Instructions for Form 1120 |
| Interest | 18 | Section 163(j) limitation | IRS Instructions for Form 1120 |
| Charitable contributions | 19 | 10% of taxable income cap | IRS Instructions for Form 1120 |
| Depreciation | 20 | Form 4562 | IRS Instructions for Form 1120 |
| Depletion | 21 | n/a | IRS Instructions for Form 1120 |
| Advertising | 22 | n/a | IRS Instructions for Form 1120 |
| Pension and profit-sharing plans | 23 | n/a | IRS Instructions for Form 1120 |
| Employee benefit programs | 24 | n/a | IRS Instructions for Form 1120 |
| Other deductions | 26 | Attached statement | IRS Instructions for Form 1120 |
Form 1120 vs 1120-S: what is the difference?
Form 1120 is for C corporations, taxed at the entity level at a flat 21%. Form 1120-S is for S corporations, which pass income through to shareholders who pay tax at their own rates. C corporations face no shareholder limits and can have foreign owners. S corporations cap at 100 shareholders and generally cannot have foreign shareholders, which pushes most international founders toward a C corporation.
| Feature | Form 1120 (C corporation) | Form 1120-S (S corporation) | Source |
|---|---|---|---|
| Who pays tax | Corporation, at entity level | Shareholders, via pass-through | IRS Instructions for Form 1120 |
| Tax rate | Flat 21% federal | Shareholder rates | 26 U.S.C. Section 11(b) |
| Shareholder limit | No limit | 100 or fewer | IRS Instructions for Form 1120 |
| Foreign shareholders | Permitted | Generally not permitted | IRS Instructions for Form 1120 |
| Due date (calendar year) | April 15 | March 15 | IRS Instructions for Form 1120 |
Commenda’s Form 1120-S guide breaks down the S corporation path in more detail.
What are the e-filing requirements for Form 1120?
Most C corporations must e-file Form 1120. Corporations that file 10 or more returns of any type during the calendar year are required to e-file, effective for returns filed on or after January 1, 2024, per the IRS Instructions for Form 1120. The count aggregates income tax returns, W-2s, 1099s, and excise returns, so the old 250-return threshold no longer shields small filers.
Corporations e-file through IRS-authorized providers and tax software. Paper filing is now the exception for active C corporations.
What are the penalties for filing Form 1120 late?
The late-filing penalty is 5% of unpaid tax per month or part of a month, capped at 25%, per the IRS failure-to-file penalty guidance. Returns more than 60 days late carry a minimum penalty. The late-payment penalty runs separately at 0.5% per month. A nil return with zero tax due may avoid the percentage penalty, but foreign-owned corporations still face the $25,000 Form 5472 penalty.
| Penalty type | Rate | Cap | Minimum | Source |
|---|---|---|---|---|
| Late filing (failure to file) | 5% of unpaid tax per month | 25% of unpaid tax | Lesser of tax due or $525 for returns due after Dec. 31, 2025 (60+ days late) | IRS failure-to-file penalty |
| Late payment | 0.5% of unpaid tax per month | 25% of unpaid tax | n/a | IRS failure-to-file penalty |
| Form 5472 non-filing | $25,000 per form | n/a | $25,000 | IRS Instructions for Form 1120 |
Interest also accrues on unpaid tax from the original due date until the balance is paid.
Do C corporations have to pay estimated taxes?
Yes. A corporation that expects to owe $500 or more in tax for the year must make quarterly estimated payments, per the IRS Instructions for Form 1120. Corporations compute installments with the Form 1120-W worksheet and pay through the Electronic Federal Tax Payment System (EFTPS). Payments are due the 15th day of the 4th, 6th, 9th, and 12th months of the tax year. Underpayment triggers a separate penalty via Form 2220.
| Installment | Calendar-year due date | Source |
|---|---|---|
| 1st | April 15 | IRS Instructions for Form 1120 |
| 2nd | June 15 | IRS Instructions for Form 1120 |
| 3rd | September 15 | IRS Instructions for Form 1120 |
| 4th | December 15 | IRS Instructions for Form 1120 |
Commenda’s Form 1120-W guide walks through the quarterly math.
What if your C corporation is foreign-owned?
A US corporation that is 25% or more foreign-owned must attach Form 5472 to its Form 1120 to report transactions with related parties. Failure to file, file on time, or keep records carries a $25,000 penalty per form, per the IRS. This is the highest-stakes trap for international founders and dormant US subsidiaries of foreign parents, because it applies even when the corporation owes zero income tax.
A single-member LLC owned by a foreign person files a pro forma Form 1120 plus Form 5472, which surprises many first-time filers. Commenda’s Form 5472 guide explains the reportable-transaction rules.
What are the most common Form 1120 mistakes?
The most common Form 1120 mistakes are skipping the nil return, filing the wrong form, missing Form 5472, misclassifying officer pay, and missing estimated payments. Each one is avoidable with the right calendar and records.
- Assuming no income means no filing: file every year regardless of activity.
- Filing Form 1120 when an S election requires Form 1120-S: confirm your election first.
- Forgetting Form 5472 when foreign-owned: attach it and avoid the $25,000 penalty.
- Confusing a Form 7004 filing extension with a payment extension: pay tax by the original due date.
- Misclassifying officer compensation as dividends: report officer pay on line 12 and Form 1125-E.
- Missing quarterly estimated payments: pay when annual tax will reach $500 or more.
How Commenda Helps With C Corporation Tax Compliance
Commenda’s corporate tax and bookkeeping service handles federal and state corporate tax filings, including Form 1120 and nil returns, on a tracked compliance calendar. Commenda closes your books, prepares the return, and confirms it got filed, so you know exactly what is due and when. For foreign-owned entities, Commenda flags Form 5472 exposure before the deadline turns it into a $25,000 penalty.
Pair the service with the Commenda compliance calendar to see every deadline by entity, and read Commenda’s complete guide to Form 1120 instructions, Form 7004 extension guide, and Form 5472 guide for the details behind each filing.
Book a demo to get a compliance calendar for your C corporation’s federal deadlines.
