Key figures
Federal compliance
2026, with sources
- Form 1120 due date
- 15th day of the 4th month after year endApril 15 for a calendar-year company. A June 30 year end keeps the 15th day of the 3rd month for tax years beginning before 2026.
- Estimated tax required
- Expected tax of $500 or moreInstallments paid electronically; underpayment penalty figured on Form 2220.
- BOI reporting for U.S. companies
- Not requiredFinCEN’s Aug 11, 2026 final rule made the March 2025 interim exemption permanent; foreign companies registered in a state still report.
The corporate return and estimated tax
A C corporation files Form 1120 every year it exists, whether or not it has income — a loss year is when the return records the net operating loss you will use later. It is due the 15th day of the 4th month after year end; Form 7004 extends the filing date by six months but the tax is still due on the original date.
Once a company expects $500 or more of tax for the year, it pays estimated tax in four installments, on the 15th day of the 4th, 6th, 9th and 12th months of its tax year, by electronic funds transfer. Form 1120-W is the worksheet; Form 2220 computes the penalty for paying late or short.
Beneficial ownership (BOI): where it landed
The Corporate Transparency Act required most small companies to report their beneficial owners to FinCEN starting in 2024. After litigation and a March 2025 interim final rule, FinCEN issued a final rule on August 11, 2026 that permanently removes the requirement for U.S. companies and U.S. persons. A domestic startup does not file a BOI report.
The rule still applies to entities formed under a foreign country’s law that have registered to do business in a US state or tribal jurisdiction. If your structure includes one — a foreign parent registered here, for example — that entity reports.
Equity and fundraising filings
Three federal filings follow equity events rather than the calendar. Founders and early employees with restricted stock file 83(b) elections. Companies report ISO exercises on Form 3921. And each priced round or SAFE raise relying on Regulation D needs a Form D with the SEC within 15 calendar days of the first sale; missing it does not void the exemption, but the SEC has brought enforcement actions for late filings.
- 83(b) election within 30 days of a restricted stock grant.
- Form 3921 for every ISO exercise: Jan 31 to the employee, Feb 28 (paper) or Mar 31 (electronic) to the IRS.
- Form D within 15 calendar days of the first sale in a Regulation D round, and an amendment annually while the offering is open.
- State “blue sky” notice filings where investors live — a state matter with its own deadlines.
Foreign owners and foreign founders
A US corporation that is at least 25% foreign-owned, or a US disregarded entity wholly owned by a foreign person, attaches Form 5472 to its return to report transactions with related foreign parties. The penalty for not filing a complete and correct form is $25,000 per form per year, with continuation penalties after an IRS notice.
Everything else on this page applies the same way to a company with foreign founders. What changes is mostly on the founders’ side — visas and their own US tax status — and on the payables side, where payments to people outside the US use Form W-8BEN and, where withholding applies, Form 1042-S.
Deadlines
- 15th day of the 4th, 6th, 9th and 12th months of the tax yearCorporate estimated tax installments, if tax for the year is expected to be $500 or moreForm 1120-W / Form 2220
- 15th day of the 4th month after year endCorporate return; Form 5472 attached if the corporation is 25% foreign-owned or a foreign-owned disregarded entityForm 1120 + Form 5472
- By the original due dateSix-month extension of time to file Form 1120Form 7004
- Within 30 days of the transferElection to be taxed on restricted stock at grantSection 83(b) election (Form 15620 or written statement)
- Within 15 calendar days after the first saleSEC notice of a Regulation D offeringForm D
- Jan 31 to employees; Feb 28 to the IRS on paper, Mar 31 if e-filedISO exercises in the prior year — to employees, then to the IRSForm 3921
Compliance, state by state
Everything above applies everywhere. Each state then adds its own rules. Choose one to read its compliance page.
Point at a state, or shade the map by one question.
Common questions
Does my Delaware C-corp have to file a BOI report?
No. FinCEN’s March 2025 interim final rule exempted companies created in the United States and their U.S. owners, and an August 11, 2026 final rule made that permanent. Only entities formed under foreign law and registered to do business in a US state still report. FinCEN also said it will delete information U.S. companies already filed.
What happens with my 83(b) election?
File it within 30 days of receiving the stock, with the IRS service center where you file your return, and give a copy to the company. You can use Form 15620 or a written statement. There is no fix for a missed window, and the election can’t be revoked without IRS consent.
Is the Delaware franchise tax a federal filing?
No — the Delaware franchise tax and annual report are state obligations, due March 1 for corporations, and they belong on Delaware’s page. The federal calendar is Form 1120, estimated tax, payroll returns, information returns and the SEC’s Form D.
Founder guides on this
- ComplianceFirst-year compliance calendar for a Delaware C-corpDelaware franchise tax, 1099s, the federal return, payroll filings, state annual reports and sales tax: the deadlines a young C-corp misses most, by month.
- SAFEsHow to account for SAFEs on your balance sheetA SAFE is cash today and shares later. Why it usually sits with liabilities, how the cap and discount set conversion, and what to book at the priced round.
- EquityStock options, 409A valuations and vesting for startupsHow option strike prices are set by a 409A valuation, how vesting and the cliff work, and why ASC 718 makes every grant an expense on your P&L.
- FundraisingAudit-ready books before your Series AInvestors, lenders and auditors ask for the same things: accrual statements, reconciled accounts and support for every balance. How to be ready first.
More of the federal guide
- AccountingFederal accounting for startupsCorporate tax, conformity to federal rules, apportionment and what it does to your books
- ReceivablesFederal receivables for startupsSales tax registration, economic nexus, whether SaaS is taxable, and collecting from customers
- PayablesFederal payables for startupsPaying vendors and contractors: 1099 filing, use tax, contractor tests and withholding
- PayrollFederal payroll for startupsWithholding, unemployment insurance, paid leave, minimum wage and the rules on paydays
- AdvisoryFederal advisory for startupsCredits, incentives and the decisions that are cheaper to get right the first time
Sources
Checked against each agency’s own page on . Rates and thresholds change, usually on January 1.
General information for US companies, not tax, legal or accounting advice for yours. Rules and thresholds change; confirm the specifics with a CPA or the agency before you act on them.