A 2026 guide to C-corp tax compliance: Form 1120 deadlines, estimated payments, board minutes, foreign-ownership rules, and what the new tax law changed.
Your C-corp's calendar year ended December 31. Somewhere between closing the books, running payroll, and actually operating the business, a handful of deadlines quietly stacked up — and April 15 is only one of them. Miss the estimated payment schedule or misread what happened to beneficial ownership reporting this year, and you're paying penalties for compliance items most owners never think about until a notice shows up.
C-corp compliance has more moving parts than S-corp or partnership compliance, mostly because a C-corp is taxed as its own entity rather than passing everything through to your personal return. That structure is exactly why the rules below matter: get them wrong and the IRS collects twice — once from the corporation, and again if it decides your retained earnings or your compliance history look like an attempt to dodge tax.
At the federal level, a C-corp has to file an annual return on Form 1120, pay quarterly estimated tax if it expects to owe $500 or more for the year, deposit payroll taxes on the same schedule as any other employer, and issue W-2s and 1099s on time. Beyond that baseline, a handful of C-corp-specific rules — the accumulated earnings tax, the corporate AMT, and (until last year) beneficial ownership reporting — exist specifically to police behavior the IRS associates with corporations, not passthrough entities.
None of this is exotic. It's mostly a calendar problem: the requirements are well-defined, the penalties are formulaic, and almost every missed deadline traces back to nobody owning the calendar rather than a genuinely hard judgment call.
A calendar-year C-corp must file Form 1120 by the 15th day of the fourth month after its tax year ends — April 15 for a corporation running on the standard calendar year. Corporations with a June 30 fiscal year-end are the one exception, with a return due the 15th day of the third month instead (September 15). Form 7004 buys an automatic six-month extension — to October 15 for a calendar-year filer — but it has to be filed by the original due date, and it extends the time to file, not the time to pay.
Miss the deadline entirely and the penalty is 5% of the unpaid tax for each month or partial month the return is late, capped at 25% . If the return is more than 60 days late, the minimum penalty for 2026 filings is the smaller of the tax owed or $525. Pay late even with a timely-filed return, and a separate penalty of 0.5% per month applies, also capped at 25% [1]. Both penalties can run at the same time, which is how a small balance due turns into a real number by the time anyone notices.
Yes — any C-corp expecting to owe $500 or more for the year has to make quarterly estimated payments, calculated on Form 1120-W. For a calendar-year corporation, the four installments are due April 15, June 15, September 15, and December 15. Note the pattern: unlike individual estimated tax, there's no January payment. The fourth corporate installment lands in December of the same tax year, not the following January — a distinction that trips up owners used to the individual schedule.
Underpay any installment and the IRS charges an underpayment penalty calculated separately for each period, which means catching up in Q4 doesn't erase what accrued in Q1 through Q3.
For most domestic C-corps, no — and this is the single most misunderstood compliance item on this list right now. FinCEN issued an interim final rule on March 26, 2025 that exempted all entities formed in the United States, and their beneficial owners, from Corporate Transparency Act reporting entirely. If your C-corp was formed under U.S. law, you're no longer required to file a BOI report, full stop.
The exemption doesn't reach everyone. Foreign entities registered to do business in the U.S. still have to report: those registered before March 26, 2025 had until April 25, 2025 to comply, and those registering after that date get 30 calendar days from their registration notice. If your corporation is domestic, treat this requirement as retired rather than pending — but don't assume the same is true for any foreign affiliate or subsidiary in your structure, and check whether your state has layered on its own beneficial-ownership filing in the meantime, since several have discussed doing exactly that.
The reconciliation law signed in July 2025 (commonly called the One Big Beautiful Bill Act) reset several provisions that had been phasing out under the original TCJA schedule, and most of the changes favor corporations that invest in equipment or R&D.
Bonus depreciation is back to 100% and made permanent for qualifying property acquired after January 19, 2025 — a reversal of the phase-down that had brought the rate to 40% [4]. Section 179 expensing rose to a $2.5 million limit with a $4 million phase-out threshold for property placed in service after December 31, 2024. And Section 174 R&D expensing — the requirement that forced companies to capitalize and amortize domestic research costs over five years starting in 2022 — was reversed for domestic research, which can again be deducted in the year it's paid or incurred; foreign R&D still has to be amortized over 15 years. Section 163(j)'s business interest limitation was also loosened, restoring the ability to add depreciation, depletion, and amortization back into the adjusted taxable income calculation, which increases how much interest expense many corporations can deduct.
If your C-corp has been capitalizing R&D costs since 2022 or sitting on bonus depreciation you assumed had phased down, this is worth revisiting with whoever prepares your return — the compliance risk here isn't missing a form, it's leaving a deduction on the table because the rule you learned two years ago no longer applies.
Almost certainly not. The corporate alternative minimum tax imposes a 15% minimum tax on adjusted financial statement income, but only for corporations averaging more than $1 billion in that income over a three-year period. It's a real compliance obligation for a small number of the largest public and private companies in the country; for a closely held C-corp well under that threshold, it isn't something your return needs to account for.
This is the one C-corp-specific compliance risk that catches profitable, cash-rich corporations off guard. The IRS can impose a 20% tax on accumulated taxable income when a corporation retains earnings beyond its reasonable business needs, and the burden is on the corporation to justify why the cash is still sitting there. Every corporation gets an automatic credit — the greater of what it can justify as needed for the business or a flat $250,000 ($150,000 for personal service corporations in fields like law, health, accounting, and consulting) — before the tax even comes into play.
In practice, this rule targets corporations that keep piling up cash with no documented plan for it — no expansion, no acquisition, no funded reserve requirement — because retaining earnings avoids the double taxation that comes with a dividend. If your C-corp has been accumulating well past that threshold, the fix isn't complicated: document the business reason in board minutes before the IRS asks for one, not after. What that documentation should actually look like is worth spelling out on its own.
Yes — and this is the compliance item most owners treat as paperwork theater until it becomes evidence in a dispute. State corporate law generally expects a corporation to hold shareholder and director meetings, keep minutes of what was decided, and document actions like stock issuances; courts weigh exactly that record when deciding whether to pierce the corporate veil in a lawsuit, not because a missing signature invalidates the corporation, but because a pattern of ignored formalities signals it isn't being run as a separate entity from its owner.
The IRS cares about the same paper trail for a different reason. When your reasonable-compensation numbers or an accumulated-earnings position get questioned, the first thing an examiner asks for is contemporaneous documentation — minutes showing who set compensation and why, a resolution authorizing a loan to a shareholder instead of a distribution, board discussion of why cash is being held back for a specific expansion or acquisition. The IRS's own guidance to its valuation professionals treats an independent compensation-setting process and clear, dated records of that process as evidence that reduces the risk of an unreasonable-compensation finding. Minutes written after the fact, once a notice has already arrived, carry far less weight than minutes written the week the decision was made.
In practice, that means a handful of board actions minuted at the time they happen, not reconstructed later: setting or changing officer compensation, approving any loan or advance between the corporation and a shareholder, authorizing a distribution or the decision not to make one, and recording the business reason behind any meaningful cash buildup. None of this needs to be elaborate — a one-page resolution, signed and dated, does the job. What it can't be is retroactive.
Beyond the big four — Form 1120, estimated tax, payroll deposits, and information returns — a few smaller items are where audits and penalty notices actually originate: 1099-NEC and 1099-MISC forms due to recipients and the IRS by January 31 (shifted to the next business day, February 2, 2026, since January 31 falls on a Saturday); state corporate income tax and franchise tax filings, which run on their own separate calendars and minimums by state; and reasonable officer compensation, which the IRS scrutinizes in both directions — too low invites payroll tax scrutiny, unreasonably high invites a disallowed deduction.
None of these is complicated in isolation. What causes problems is treating C-corp compliance as one annual event instead of a year-round calendar with four or five recurring touch points.
Yes, and they layer on top of everything above rather than replacing it. A domestic C-corp with at least one foreign person or entity owning 25% or more of its stock — directly or indirectly, by vote or by value — becomes what the IRS calls a 25%-foreign-owned reporting corporation, which triggers three separate obligations most owners don't find out about until a lender, investor, or accountant asks [10].
The first is Form 5472, filed as an attachment to Form 1120 by the same due date, including extensions. It reports transactions between the corporation and its foreign (or domestic) related parties — capital contributions, intercompany loans, management fees, and similar dealings. The penalty for missing it isn't graduated the way the late-filing penalty on Form 1120 is: it's a flat $25,000 per reporting corporation right out of the gate, with another $25,000 for every 30-day period the failure continues past 90 days after the IRS notifies you. A corporation that assumes “we didn't have much activity, so it probably doesn't apply” is exactly the profile the IRS built this penalty for.
The second is withholding on U.S.-source income paid to the foreign shareholder — most commonly dividends. The default withholding rate is 30%, reported on Forms 1042 and 1042-S, though a tax treaty between the shareholder's home country and the U.S. can reduce that rate or eliminate it entirely if the paperwork establishing treaty eligibility is filed correctly. This is distinct from a foreign corporation running a U.S. branch, which is a different structure entirely (Form 1120-F, not Form 1120) — don't let the two get confused when you're researching which rules apply to you.
The third is easy to miss because it isn't run by the IRS at all: the Bureau of Economic Analysis requires a BE-13 filing within 45 days of a foreign investor acquiring at least a 10% voting interest in a U.S. business, establishing a new U.S. entity, or expanding an existing one. It's a data-collection survey, not a tax form, but it's mandatory, and “nobody told us about it” isn't a defense a company hears back.
A few requirements only kick in once a C-corp crosses a size or activity threshold, which is exactly why they get missed — nobody was tracking for them at formation, and by the time they apply, compliance has already settled into a routine that doesn't include them.
Cross 50 full-time-equivalent employees averaged over the prior year and the corporation becomes an “applicable large employer” under the ACA, which brings employer-mandate exposure and annual Forms 1094-C and 1095-C reporting on the health coverage offered to employees. Sponsor a 401(k) or other ERISA retirement plan and the plan administrator has to file Form 5500 each year — July 31 for a calendar-year plan, with an extension available on Form 5558. And if the corporation sells into other states, economic nexus rules mean sales tax collection obligations can exist in a state with no physical presence at all; most states trigger nexus around $100,000 in sales, though the exact figure, whether a transaction count also counts, and what counts as a taxable sale all vary by state.
None of these are exotic once you know to look for them. They're just the kind of thing a compliance calendar built at formation never accounted for, because the business hadn't grown into them yet.
Do C-corps really get taxed twice?
Yes — a C-corp pays 21% corporate tax on its profits, and shareholders pay tax again on any dividends the corporation distributes out of those after-tax earnings. Salary, retained earnings reinvested in the business, and certain other structures can reduce how much income actually gets hit twice, which is why C-corp tax planning is a separate conversation from just filing the return correctly.
What happens if I file Form 1120 late with no tax owed?
The 5%-per-month late-filing penalty is based on unpaid tax, so if the return shows zero balance due, the dollar penalty is minimal — but a pattern of late filing still creates a compliance record the IRS notices, and it can complicate an extension request or penalty abatement down the road.
Can I still get a filing extension for my C-corp return?
Yes. Filing Form 7004 by the original due date gets you an automatic six-month extension — to October 15 for a calendar-year corporation — but the extension only applies to filing the return, not to paying the tax you owe.
Does the beneficial ownership exemption apply to my LLC that elected C-corp taxation?
If the entity was formed domestically, the March 2025 exemption applies regardless of how it elected to be taxed for federal income tax purposes — BOI reporting is a Corporate Transparency Act requirement tied to how the entity was formed, not how it's taxed.
Do we still need to file Form 5472 if our foreign-owned C-corp barely did anything this year?
Probably. Form 5472 is required when a 25%-foreign-owned reporting corporation has a reportable transaction with a related party during the year, and things owners assume are too small to count — a capital contribution from the parent, an intercompany loan, a management fee — generally qualify. Given the flat $25,000 starting penalty, most advisors treat “we're not sure it applies” as a reason to file, not a reason to skip it.
If your C-corp's calendar has more question marks on it than dates — or those retained earnings have been piling up without a documented business reason behind them — a short conversation with us can close that gap before a notice does it for you.
[1] "About Form 1120, U.S. Corporation Income Tax Return" — IRS.gov, irs.gov/instructions/i1120, accessed August 2026.
[2] "Publication 542, Corporations" — IRS.gov, irs.gov/publications/p542, accessed August 2026.
[3] "FinCEN Removes Beneficial Ownership Reporting Requirements for U.S. Companies and U.S. Persons" — FinCEN.gov, fincen.gov/news/news-releases/fincen-removes-beneficial-ownership-reporting-requirements-us-companies-and-us, accessed August 2026.
[4] "Key Changes to Bonus Depreciation, Section 179 and Section 174 from the One Big Beautiful Bill Act" — Anders CPA, anderscpa.com/learn/blog/obbb-bonus-depreciation-section-179-section-174-one-big-beautiful-bill-act, accessed August 2026.
[5] "Corporate Alternative Minimum Tax" — IRS.gov, irs.gov/inflation-reduction-act-of-2022/corporate-alternative-minimum-tax, accessed August 2026.
[6] "26 U.S. Code § 531 — Imposition of accumulated earnings tax" — Cornell Law School Legal Information Institute, law.cornell.edu/uscode/text/26/531, accessed August 2026.
[7] "26 U.S. Code § 535 — Accumulated taxable income" — Cornell Law School Legal Information Institute, law.cornell.edu/uscode/text/26/535, accessed August 2026.
[8] "Piercing the Veil of Small Business: What the Owners of LLCs and Corporations Need to Know" — Wolters Kluwer, wolterskluwer.com/en/expert-insights/piercing-the-veil-of-small-business-what-the-owners-of-llcs-and-corporations-need-to-know, accessed August 2026.
[9] "Reasonable Compensation Job Aid for IRS Valuation Professionals" — IRS.gov, irs.gov/pub/irs-lbi/Reasonable Compensation Job Aid for IRS Valuation Professionals.pdf, accessed August 2026.
[10] "Instructions for Form 5472" — IRS.gov, irs.gov/instructions/i5472, accessed August 2026.
[11] "NRA Withholding" — IRS.gov, irs.gov/individuals/international-taxpayers/nra-withholding, accessed August 2026.
[12] "International Surveys: Foreign Direct Investment in the United States (BE-13)" — U.S. Bureau of Economic Analysis, bea.gov/surveys/fdiusurv, accessed August 2026.
[13] "Employer Shared Responsibility Provisions" — IRS.gov, irs.gov/affordable-care-act/employers/employer-shared-responsibility-provisions, accessed August 2026.
[14] "Form 5500 Corner" — IRS.gov, irs.gov/retirement-plans/form-5500-corner, accessed August 2026.
[15] "Sales Tax Nexus by State: 2026 Rules & Thresholds" — TaxCloud, taxcloud.com/blog/sales-tax-nexus-by-state, accessed August 2026.
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