Guides
Form 1120 Explained: The C Corporation Tax Return
Form 1120 is the annual U.S. federal income tax return that a C corporation files to report its income, deductions, credits, and tax. The corporation pays a flat 21% federal rate on its taxable income. For a calendar-year corporation, the 2025 return is due April 15, 2026. Most domestic corporations must file even in a year with no income.
Below is what the form covers, the rate, the deadlines, the estimated-payment rules, the main schedules, and how the C corporation return differs from the S corporation return on Form 1120-S.
What Form 1120 is and who files it
Form 1120 reports a C corporation’s income, deductions, and federal income tax for the year. Nearly every domestic corporation must file it, including corporations with no taxable income and corporations in bankruptcy, until the entity is formally dissolved. An LLC that elects corporate treatment on Form 8832 files it too.
The return runs the same arithmetic each year: gross income, minus allowable deductions, equals taxable income, which is multiplied by the tax rate to reach the tax. Estimated payments and credits are then subtracted to find the balance due or the refund.
A corporation files whether or not it distributed dividends. The filing obligation attaches to the entity’s existence, not to its profitability, which is why a dormant corporation still owes a return. Filing can generally be done electronically, and corporations meeting IRS e-file thresholds may be required to e-file.
The 21% flat corporate tax rate
C corporation taxable income is taxed at a flat 21% federal rate. The Tax Cuts and Jobs Act set this single rate for tax years beginning after December 31, 2017, replacing the earlier graduated schedule that topped out at 35%. There are no corporate brackets: the first dollar and the millionth dollar of taxable income are taxed the same.
The 21% figure is the statutory federal rate under Internal Revenue Code Section 11. A corporation’s effective rate can differ because credits, deductions, and book-to-tax differences change the base the rate applies to.
State corporate income tax may apply on top of the federal 21%, and rates and rules vary by state. Some states impose a flat corporate rate, some use brackets, and a few impose gross-receipts or franchise taxes instead. See our Texas franchise tax margin tax guide and the Delaware franchise tax calculation for two common examples of state-level entity taxes.
C corporation profits can face a second layer of tax: earnings distributed as dividends are generally taxed again on shareholders’ individual returns. That two-layer result is the double taxation that shapes many entity-choice decisions.
The April 15 filing deadline and extensions
A calendar-year C corporation must file Form 1120 by the 15th day of the fourth month after year-end, which is April 15 for a December 31 year-end. The 2025 return is due April 15, 2026. If the date falls on a weekend or legal holiday, the deadline moves to the next business day.
Fiscal-year corporations follow the same “15th day of the fourth month” rule applied to their own year-end. A corporation with a June 30 fiscal year-end has a special deadline: its return is due the 15th day of the third month (September 15), a rule that runs through tax years beginning before 2026 under current transition provisions.
A corporation can request an automatic six-month extension by filing Form 7004 on or before the original due date. For a calendar-year filer, that moves the filing deadline to October 15. The extension covers filing only, not payment. Tax owed is still due by the original deadline, and interest and penalties can accrue on unpaid amounts. See Form 7004 for business extensions for the mechanics.
Corporate estimated tax payments
A C corporation that expects to owe $500 or more in federal income tax for the year must pay in installments during the year. Payments are due by the 15th day of the 4th, 6th, 9th, and 12th months of the tax year. For a calendar-year corporation, that means April 15, June 15, September 15, and December 15.
Each installment generally equals 25% of the required annual payment. The required annual payment is the lesser of these two amounts:
- Current-year method: 100% of the tax shown on the current year’s return.
- Prior-year safe harbor: 100% of the tax shown on the prior year’s return (available only if that return covered 12 months and showed a positive tax).
A “large corporation,” defined as one with $1 million or more of taxable income in any of the three preceding tax years, generally cannot use the prior-year safe harbor. It may use the prior-year amount only for its first installment and must then true up. Corporations pay through the Electronic Federal Tax Payment System (EFTPS). Underpayment is figured on Form 2220. Our estimated tax payments guide covers the individual and entity rules side by side.
Key schedules on Form 1120
Form 1120 attaches several schedules that build the return. Some appear on the form itself, and others are separate attachments filed when thresholds are met. The table below summarizes the ones most corporations encounter.
| Schedule | Name | What it does |
|---|---|---|
| Schedule C | Dividends, Inclusions, and Special Deductions | Reports dividend income and computes the dividends-received deduction |
| Schedule J | Tax Computation and Payment | Calculates total tax, applies credits, and reports estimated payments |
| Schedule K | Other Information | Reports accounting method, business activity, ownership, and related-party facts |
| Schedule L | Balance Sheets per Books | Beginning and end-of-year balance sheet from the corporation’s books |
| Schedule M-1 | Reconciliation of Income (Loss) per Books | Reconciles book income to taxable income for smaller corporations |
| Schedule M-2 | Analysis of Unappropriated Retained Earnings | Tracks changes in retained earnings during the year |
| Schedule M-3 | Net Income (Loss) Reconciliation | Detailed book-tax reconciliation required for corporations with $10M or more in total assets |
Schedules L, M-1, and M-2 are generally not required if the corporation’s total receipts and total assets are each under $250,000 for the year, though many corporations complete them anyway. Corporations with $10 million or more in total assets file Schedule M-3 in place of M-1. The dividends-received deduction on Schedule C can equal 50%, 65%, or 100% of qualifying dividends depending on the corporation’s ownership stake in the payer.
Form 1120 vs Form 1120-S: C corp vs S corp
The core difference is who pays the tax. A C corporation files Form 1120 and pays the 21% federal tax at the entity level. An S corporation files Form 1120-S, generally pays no federal income tax itself, and passes income, deductions, and credits through to shareholders, who report their shares on their own returns via Schedule K-1.
| Feature | Form 1120 (C corp) | Form 1120-S (S corp) |
|---|---|---|
| Entity type | C corporation | S corporation |
| Federal tax | 21% at the entity level | Generally none at the entity level |
| Taxation of profits | Taxed at corporation, then again on dividends | Passed through, taxed once on shareholder returns |
| Election required | None | Form 2553 |
| Shareholder limit | No limit | 100, with eligibility restrictions |
| Calendar-year deadline | April 15 | March 15 |
| Pass-through reporting | No | Yes, via Schedule K-1 |
Note the different deadlines: the S corporation return is due one month earlier, on March 15 for a calendar-year filer. To become an S corporation, an eligible corporation files Form 2553 to elect S corporation status. For a fuller comparison across entity types, see our business entity comparison. Shareholders read their pass-through amounts on the Schedule K-1.
Frequently asked questions
Who has to file Form 1120?
Most domestic C corporations must file Form 1120, including corporations with no income and corporations in bankruptcy, until they formally dissolve. LLCs and other eligible entities that elect corporate treatment on Form 8832 also file it. The obligation follows the entity’s legal existence, so a dormant corporation still files a return for the year.
What is the corporate tax rate on Form 1120?
C corporation taxable income is taxed at a flat 21% federal rate under Internal Revenue Code Section 11, with no brackets. The Tax Cuts and Jobs Act set this rate for tax years beginning after December 31, 2017. State corporate taxes may apply on top and vary by state. A corporation’s effective rate can differ from 21% because of credits and book-to-tax differences.
When is Form 1120 due in 2026?
A calendar-year C corporation’s 2025 Form 1120 is due April 15, 2026, the 15th day of the fourth month after year-end. Fiscal-year corporations use the same rule applied to their year-end. Filing Form 7004 by the original due date grants an automatic six-month extension to October 15 for calendar-year filers, but tax owed is still due April 15.
Does a C corporation have to make estimated tax payments?
Yes, if it expects to owe $500 or more in federal income tax for the year. Payments are due by the 15th day of the 4th, 6th, 9th, and 12th months. Each installment is generally 25% of the required annual payment, which is the lesser of 100% of the current-year tax or 100% of the prior-year tax. Large corporations generally cannot use the prior-year safe harbor.
What is the difference between Form 1120 and Form 1120-S?
Form 1120 is the C corporation return, and the corporation pays a 21% federal tax at the entity level. Form 1120-S is the S corporation return, and the entity generally pays no federal income tax, passing income to shareholders on Schedule K-1 instead. An S corporation must first elect that status on Form 2553. The S corporation return is due one month earlier, on March 15 for calendar-year filers.
What schedules are filed with Form 1120?
Common schedules include Schedule C (dividends and special deductions), Schedule J (tax computation), Schedule K (other information), Schedule L (balance sheet), Schedule M-1 (book-to-tax reconciliation), and Schedule M-2 (retained earnings). Corporations with $10 million or more in total assets file Schedule M-3 instead of M-1. Schedules L, M-1, and M-2 may be skipped when receipts and assets are each under $250,000.
Reviewed by The Ledgerism Editorial Team. Last reviewed: July 2026.