Which federal return a business files is decided by its federal tax classification and by any election made to change it, not by the name on the formation certificate. Get those right and the calendar follows. Get them wrong and the penalty is charged per owner per month, which is how a four-owner business ends up owing several thousand dollars on a return reporting no tax at all.
Which Return Your Entity Files
The federal tax return your business files depends on its FEDERAL TAX CLASSIFICATION, not on its state-law form. An LLC under state law can be taxed as a sole proprietorship (disregarded), partnership, S-corp, or C-corp. The classification determines the return.
Disregarded entity (single-member LLC default): files Schedule C as part of the owner's Form 1040. No separate entity-level return.
Partnership (multi-member LLC default): files Form 1065. Each partner receives a Schedule K-1 reporting their share of income.
S-corporation (entity that filed Form 2553): files Form 1120-S. Each shareholder receives a Schedule K-1.
C-corporation (corporation default; LLC that filed Form 8832 electing C-corp): files Form 1120. The entity pays corporate tax at 21% federal. Distributions to shareholders are taxed again as dividends.
The state law wrapper therefore tells you little about the filing. An LLC can sit in any of the four rows above and move between them. A single-member LLC is disregarded and files nothing of its own; add a second member and the same entity files Form 1065 from that date, with no change to the certificate of formation. Where profit is taxed is covered in LLC taxes, and whether to move onto the S corporation row in when to actually switch.
Form 1120 (C-Corporation)
At a Glance
| Item | Value |
|---|---|
| C-Corporation | Form 1120, April 15 deadline |
| S-Corporation | Form 1120-S, March 15 deadline |
| Partnership | Form 1065, March 15 deadline |
| Sole Proprietor | Schedule C (on Form 1040), April 15 deadline |
| Extension | Form 7004 (entities) or 4868 (individuals), 6 months |
Form 1120 is the US Corporation Income Tax Return. Filed by C-corporations and by LLCs that elected C-corp treatment via Form 8832.
Deadline: the 15th day of the 4th month after the end of the tax year, so April 15, 2027 for calendar year 2026. One exception is worth knowing: a corporation with a tax year ending June 30 files by the 15th day of the 3rd month instead, and takes a 7 month extension rather than 6.
Tax rate: 21% federal flat rate on net income.
Extensions: Form 7004 extends the filing deadline 6 months, to October 15, 2027 for a calendar year 2026 return. The extension does not extend the time to pay. Estimated tax must be with the IRS by April 15 or the late payment charge starts running from that date regardless of the extension.
Key schedules: Schedule J (tax computation), Schedule K (other information), Schedule L (balance sheet), Schedule M-1 (reconciliation of income), Schedule M-2 (analysis of unappropriated retained earnings).
Foreign-owned C-corp considerations: Form 5472 is required if any 25%+ shareholder is a foreign person. This is in addition to Form 1120.
Compliance monitoring
If you would rather not do this yourself, we track every deadline for your entity and file on time, in every state where you are registered. Or keep reading and file it on your own. This guide covers everything you need either way.
Form 1120-S (S-Corporation)
Form 1120-S is the US Income Tax Return for an S Corporation. Filed by S-corporations and by entities that elected S-corp treatment via Form 2553.
Deadline: March 15 for calendar-year entities (15th day of the 3rd month after fiscal year end). This is one month EARLIER than the C-corp 1120 deadline.
Tax flow: the S-corp itself generally does not pay federal income tax. Net income flows to shareholders via Schedule K-1, taxed on their personal returns.
Reasonable salary requirement: S-corp owners who work in the business must pay themselves a reasonable salary via W-2 payroll BEFORE taking distributions. The 1120-S reports wages and distributions separately.
Built-in gains tax: S-corps that were previously C-corps may owe built-in gains tax on appreciated assets held at the time of conversion.
Extensions: Form 7004 extends the filing deadline 6 months to September 15.
Late filing penalty: for returns required to be filed in 2027, $260 per shareholder for each month or part month, capped at 12 months, charged even when no tax is owed. For a four-shareholder S corporation three months late that is $3,120. The figure is adjusted for inflation annually; it was $255 for returns required to be filed in 2026.
Form 1065 (Partnership)
Form 1065 is the US Return of Partnership Income. Filed by general partnerships, limited partnerships, limited liability partnerships, and multi-member LLCs taxed as partnerships.
Deadline: March 15 for calendar-year entities (same as 1120-S, one month earlier than 1120).
Tax flow: the partnership itself does not pay federal income tax. Net income flows to partners via Schedule K-1, taxed on their personal returns.
Schedule K-1 issuance: each partner receives a K-1 reporting their share of income, deductions, credits and other items. K-1s are furnished to partners by the return's due date, March 15, 2027 for calendar year 2026, or by the extended date if the partnership extends. Partners cannot finish their personal returns until the K-1 arrives, which is why a partnership that extends effectively extends every partner.
Extensions: Form 7004 extends the filing deadline 6 months to September 15.
Late filing penalty: $260 per partner for each month or part month, capped at 12 months, for returns required to be filed in 2027. Same structure as the S corporation charge, and it applies whether or not the partnership owed anything.
A second, separate charge covers the Schedule K-1s. Failure to furnish a correct K-1 when due carries a per-statement penalty, $340 in the current Form 1065 instructions, with a higher figure for intentional disregard. A partnership that files its 1065 on time and never sends the K-1s has not finished.
Self-employment tax: partnership income flowing to general partners is subject to self-employment tax (15.3%). This is one of the reasons many partnerships convert to S-corps once profitable.
Schedule C (Sole Proprietor / Disregarded SMLLC)
Schedule C is filed as part of the owner's personal Form 1040. It reports the income and expenses of a sole proprietorship or a disregarded single-member LLC.
Deadline: April 15 (the personal Form 1040 deadline) for calendar-year activity.
Tax flow: net Schedule C income is added to the owner's other personal income and taxed at personal rates, and is also subject to self-employment tax at 15.3% up to the Social Security wage base, which is $184,500 for 2026, then 2.9% Medicare only above that. The base moved from $176,100 for 2025, so use the 2026 figure when modelling an S corporation election.
Extensions: Form 4868 extends the personal return filing deadline 6 months to October 15.
Common Schedule C deductions: home office (Form 8829), vehicle expenses, depreciation (Form 4562), and the qualified business income deduction (Form 8995 or 8995-A).
No separate return for the SMLLC: a single-member LLC that has not elected corporate treatment files everything on the owner's Form 1040. The LLC has no federal filing requirement of its own.
Foreign-Owned SMLLC: Special Case
A US single-member LLC owned by a foreign person is a disregarded entity for federal tax purposes, but Form 5472 + proforma Form 1120 are still required EVERY YEAR. This is the rule that catches many foreign founders by surprise.
The proforma Form 1120 is NOT a tax return in the normal sense. All income lines are zero. It exists solely to serve as a vehicle for Form 5472, which reports related-party transactions with the foreign owner.
The foreign owner's actual income from the SMLLC is reported on the owner's home-country tax return (and possibly on Form 1040-NR if US tax obligations exist). The proforma 1120 does not report income, only the existence of the entity.
Penalties for missing Form 5472: $25,000 per form per year. We cover this in detail in our Form 5472 article.
How Extensions Work
Form 7004: extends the deadline for entity returns (1120, 1120-S, 1065) by 6 months. Filed by the original due date. No reason required.
Form 4868: extends the deadline for personal returns (Form 1040, including Schedule C) by 6 months. Filed by the original due date.
Critical: extensions extend TIME TO FILE, not TIME TO PAY. Estimated tax due must be paid by the original deadline. Late-payment penalties accrue from the original due date even with an extension.
Failure-to-file penalty: 5% of unpaid tax per month, up to 25%. Filing an extension avoids this.
Failure to pay penalty: 0.5% of unpaid tax per month, up to 25%. It cannot be avoided by an extension, only by paying. Because the failure to file charge is ten times the failure to pay charge, the right move in a bad cash month is always to file on time and pay late, never the reverse.
One more figure for corporate returns: for a return required to be filed in 2026 that is more than 60 days late, the minimum penalty is the smaller of the tax due or $525, whatever the percentage arithmetic would otherwise produce.
Three Filing Seasons in Practice
The three below are composites of entities on these forms. The federal dates and penalty figures are the real ones; the business facts are illustrative.
Example 1: Third Coast Print Works misses March 15
A four-shareholder S corporation in Milwaukee had a profitable year, distributed everything, and owed no entity-level tax. Its bookkeeper was on leave in February, nobody filed Form 7004, and Form 1120-S went in on June 20. Four months late counting part months, at $260 per shareholder per month, is $4,160 on a return with no tax on it. Form 7004 would have removed all of it for ten minutes of work in early March. The shareholders could not file personally without K-1s either, so one missed date became five late filings.
Example 2: Ellery Grove Partners and nine sets of personal returns
A nine-partner real estate LLC taxed as a partnership extends every year and files Form 1065 in September. That is legitimate, and it pushes nine individual returns to October, because no partner can file without a K-1. If it slipped past the extended date the exposure would be $260 times nine partners per month, $2,340 for one month, before the separate per-K-1 charge. Habitual extenders should treat September 1 as the internal deadline. How profit reaches the partners is covered in how to pay yourself from your LLC.
Example 3: Vantage Grid Energy extends and still gets a bill
A C corporation with $1.4m of taxable income filed Form 7004 by April 15, 2027 and the return in October, paying nothing in April on the theory that the extension covered it. The extension covered the return, not the money. Federal tax at 21% on $1.4m is $294,000, and the failure to pay charge at 0.5% a month runs from April 15: roughly $1,470 a month, near $8,800 over six months, plus interest. Pay an estimate with the extension and true it up in October. The entity comparison is in C corporation versus S corporation and what is an S corporation.
Common Federal Return Mistakes
Five failures account for most of the notices that follow a filing season. Four of the five are calendar problems rather than tax problems.
Mistake 1: Working to April 15 when the entity is due March 15
What happens. An owner who has filed a personal return every April assumes the business follows the same date. Why it fails. Form 1065 and Form 1120-S are due the 15th day of the 3rd month, a full month before the individual deadline. Consequence. $260 per partner or shareholder for each month or part month, up to 12 months, with no tax owed required. Prevention. Put March 15 in the calendar with a February 1 warning, and file Form 7004 rather than gambling on the date.
Mistake 2: Filing the entity return and not issuing the K-1s
What happens. The 1065 or 1120-S is filed on time and the K-1s follow weeks later. Why it fails. Furnishing the statement to the owner is a separate obligation from filing the return, with its own penalty per statement. Consequence. A per-K-1 charge on top of anything else, and owners who cannot file personally until the document arrives. Prevention. Treat the return and the K-1 distribution as one task with one date.
Mistake 3: Reading an extension as an extension to pay
What happens. Form 7004 or Form 4868 goes in, and nothing is paid until the return is filed. Why it fails. Both forms extend time to file only. Tax is due on the original date. Consequence. 0.5% of the unpaid tax per month, to a 25% cap, plus interest running from the original due date. Prevention. Pay an estimate with the extension. Overpaying is recoverable; underpaying is not free.
Mistake 4: A foreign-owned single-member LLC filing nothing at all
What happens. The owner reads that a disregarded entity has no federal return and files none. Why it fails. A foreign-owned US disregarded entity must file Form 5472 attached to a pro forma Form 1120 every year, whether or not it had income or activity. Consequence. $25,000 per year, with a further $25,000 for each 30 day period once the failure continues more than 90 days after IRS notification. Prevention. Diarise it at formation. The full requirement is in the Form 5472 guide.
Mistake 5: An S corporation with large distributions and no salary
What happens. Form 1120-S reports substantial distributions to an active owner and no officer compensation. Why it fails. An owner who works in the business must be paid a reasonable salary through payroll first. Consequence. Recharacterised wages across open years, Social Security and Medicare on the recharacterised amount, and deposit penalties on every missed Form 941 deposit. Prevention. Set the salary before the first distribution and document how; reasonable salary covers the benchmarking.
The Penalties, in Dollars
Four charges cover almost everything that goes wrong with these returns.
Late partnership or S corporation return. $260 per partner or shareholder for each month or part month, up to 12 months, for returns required to be filed in 2027. It applies with no tax due. A six-owner entity three months late owes $4,680. The same entity a full year late reaches the 12 month cap at $18,720.
Late corporate or individual return with tax owed. 5% of the unpaid tax per month or part month, capped at 25%. For a return required to be filed in 2026 that is more than 60 days late, the minimum is the smaller of the tax due or $525.
Late payment. 0.5% of the unpaid tax per month, capped at 25%, running from the original due date whether or not an extension was filed, plus interest.
Missing information returns. K-1s not furnished carry $340 per statement in the current Form 1065 instructions. Form 5472, for a foreign-owned entity, carries $25,000 a year.
Two patterns follow. Filing on time with an unpaid balance costs a tenth of filing late, so file first and pay second when both are impossible. And the flow-through penalties scale with the number of owners rather than the size of the business, which is why the most exposed entity here is often the smallest one with the most members. Current bookkeeping is what makes the March date achievable.
How File.Business Handles Federal Returns
File.Business partners with CPAs to handle federal tax return preparation for our entity-formation and ongoing-compliance clients. We coordinate the data collection (financial statements, expense receipts, K-1s from any entities the client owns), the CPA prepares the appropriate return (1120, 1120-S, 1065, or Schedule C), and we ensure timely filing with the IRS.
For foreign-owned SMLLCs: we handle Form 5472 + proforma Form 1120 directly (not delegated to a CPA partner), since these are entity-existence filings rather than income returns.
Pricing: federal tax return preparation is priced by complexity (number of K-1s, number of states, foreign income, etc.). Starting prices: $549 for Schedule C, $899 for 1065 or 1120-S, $1,299 for 1120. Foreign-owned SMLLC Form 5472 + proforma 1120: $399 (covered separately).
Frequently Asked Questions
What federal tax return does my LLC file?
Depends on the LLC's federal tax classification. Single-member LLC default: Schedule C on the owner's 1040. Multi-member LLC default: Form 1065. LLC that elected S-corp: Form 1120-S. LLC that elected C-corp: Form 1120.
When are Form 1065 and Form 1120-S due?
March 15 for calendar-year entities (one month earlier than the April 15 personal Form 1040 deadline). Extensions to September 15 are available via Form 7004.
When is Form 1120 due?
April 15 for calendar-year entities. Extensions to October 15 are available via Form 7004.
Does an extension also extend the time to pay tax?
No. Form 7004 and Form 4868 extend the time to FILE only. Estimated tax must be paid by the original deadline to avoid late-payment penalties. Late-payment penalty is 0.5% per month, up to 25%.
What is the penalty for late-filing Form 1120-S or 1065?
For returns required to be filed in 2027, $260 per shareholder or partner for each month or part month, capped at 12 months. For a four-shareholder S corporation filing three months late that is $3,120, even if no tax is owed. The amount is adjusted for inflation each year.
Does a foreign-owned single-member LLC have to file a federal return?
Yes. Form 5472 + proforma Form 1120 are required every year. This is true even if the LLC has no US source income or business activity. Penalty for missing: $25,000 per form per year.
Can File.Business prepare my federal tax return?
Yes. We partner with CPAs to prepare federal returns for our clients. Starting prices: $549 for Schedule C, $899 for 1065/1120-S, $1,299 for 1120. Foreign-owned SMLLC Form 5472 + proforma 1120: $399.
File.Business handles federal compliance for you
From EIN to Form 5472, federal filings stack up fast. File.Business pairs your entity with the right federal filings on a single calendar, with deadline tracking, automatic preparation, and CPA partnership for income tax returns.
This guide is written from the official sources below. Fees, forms, and deadlines change; confirm the current requirement with the agency before you file.
Disclosure. File.Business is a private filing service, not a government agency and not a law firm. We prepare and submit filings at your direction, and nothing on this page is legal or tax advice. Filing fees, deadlines, and statutory references are current as of the last-updated date shown above and can change. Confirm current requirements with the relevant state agency before you file.
