Tax dates

Last updated: March 17, 2025

Federal Tax and Compliance Requirements for a C-Corp Startup

Step 1: Understand Your Tax Obligations

  • Corporate Income Tax: As a C-Corp, your business is a separate taxpaying entity subject to federal corporate income tax (currently a flat 21% rate as of 2025, unless changed by legislation). Profits are taxed at the corporate level, and dividends distributed to shareholders are taxed again at the individual level (double taxation).

  • Estimated Taxes: If your C-Corp expects to owe $500 or more in taxes for the year, you must make quarterly estimated tax payments.

  • Employment Taxes: If you have employees, you’re responsible for withholding income taxes, Social Security, and Medicare (FICA), as well as paying Federal Unemployment Tax (FUTA).

  • Additional Reporting: Depending on your activities (e.g., employee stock options, R&D credits), additional forms may apply.

Step 2: Key Forms and Deadlines

Here’s a breakdown of the primary federal forms, their purposes, and deadlines for a calendar-year C-Corp in 2025:

  1. Form 1120: U.S. Corporation Income Tax Return

    • Purpose: Reports your C-Corp’s income, deductions, credits, and tax liability for the 2024 tax year.

    • Deadline: April 15, 2025 (the 15th day of the 4th month after the tax year ends).

    • Extension: File Form 7004 by April 15, 2025, for an automatic 6-month extension to October 15, 2025. Note: This extends the filing deadline, not the payment deadline—taxes owed must still be paid by April 15.

    • Link: Form 1120

  2. Form 7004: Application for Automatic Extension

    • Purpose: Requests a 6-month extension to file Form 1120.

    • Deadline: April 15, 2025 (must be filed before the original due date).

    • Link: Form 7004

  3. Quarterly Estimated Tax Payments

    • Purpose: Prepay your corporate income tax liability in four installments if you expect to owe $500 or more.

    • Deadlines for 2025:

      • 1st Quarter: April 15, 2025 (for January–March)

      • 2nd Quarter: June 16, 2025 (for April–May; adjusted for weekend)

      • 3rd Quarter: September 15, 2025 (for June–August)

      • 4th Quarter: December 15, 2025 (for September–November)

    • How to Pay: Use the Electronic Federal Tax Payment System (EFTPS) at EFTPS.gov.

    • Note: Calculate each payment as 25% of the lesser of your expected 2025 tax or your 2024 tax liability (if 2024 was a full 12-month year with positive tax).

  4. Form 941: Employer’s Quarterly Federal Tax Return

    • Purpose: Reports withheld income taxes, Social Security, and Medicare taxes for employees.

    • Deadlines for 2025:

      • Q1 (Jan–Mar): April 30, 2025

      • Q2 (Apr–Jun): July 31, 2025

      • Q3 (Jul–Sep): October 31, 2025

      • Q4 (Oct–Dec): January 31, 2026

    • Deposits: Payroll tax deposits are due monthly or semi-weekly, depending on your liability. Check IRS Publication 15 for your schedule.

    • Link: Form 941

  5. Form 940: Employer’s Annual Federal Unemployment (FUTA) Tax Return

    • Purpose: Reports your FUTA tax liability (0.6% on the first $7,000 of each employee’s wages after a credit).

    • Deadline: January 31, 2026 (for 2025 wages).

    • Link: Form 940

  6. Form W-2: Wage and Tax Statement

    • Purpose: Reports wages and taxes withheld for each employee to the IRS and the employee.

    • Deadline: January 31, 2026 (provide copies to employees and file with the Social Security Administration).

    • Link: Form W-2

  7. Form 1099-NEC: Nonemployee Compensation

    • Purpose: Reports payments of $600 or more to independent contractors.

    • Deadline: January 31, 2026 (to recipients and IRS).

    • Link: Form 1099-NEC

  8. Form 3921: Exercise of an Incentive Stock Option (ISO)

    • Purpose: Required if employees exercised ISOs in 2025.

    • Deadline: February 28, 2026 (paper filing) or March 31, 2026 (electronic filing).

    • Link: Form 3921

  9. Form 6765: Credit for Increasing Research Activities

    • Purpose: Claims the R&D tax credit if your startup conducted qualifying research (common for tech startups).

    • Deadline: File with Form 1120 (April 15, 2025, or October 15, 2025 with extension).

    • Link: Form 6765

  10. ACA Forms (1094-C and 1095-C) (if applicable)

    • Purpose: Reports health insurance coverage for employees if your C-Corp has 50+ full-time equivalent employees (Applicable Large Employer under ACA).

    • Deadline:

      • Furnish 1095-C to employees: January 31, 2026

      • File 1094-C/1095-C with IRS: February 28, 2026 (paper) or March 31, 2026 (electronic)

    • Link: Form 1094-C, Form 1095-C

  11. Beneficial Ownership Information (BOI) Report (Corporate Transparency Act)

    • Purpose: Reports beneficial owners (individuals with 25%+ ownership or substantial control) to FinCEN. Required for most C-Corps formed before or after January 1, 2024, unless exempt (e.g., large operating companies with 20+ employees and $5M+ revenue).

    • Deadline:

      • If formed before January 1, 2024: March 21, 2025 (extended deadline due to FinCEN updates).

      • If formed in 2025: Within 90 days of incorporation (e.g., June 15, 2025, if incorporated March 17, 2025).

    • How to File: Submit online at FinCEN BOI E-Filing.

    • Note: This is a one-time filing unless ownership/control changes.

Step 3: Additional Compliance Considerations

  • Electronic Filing Mandate: If your C-Corp files 10 or more returns in 2025 (e.g., W-2s, 1099s, 1120), you must e-file using a Transmitter Control Code (TCC). Apply at IRS FIRE System.

  • State Taxes: Check your state’s requirements (see Step 4 below).

  • Recordkeeping: Maintain accurate records of income, expenses, payroll, and tax filings for at least 3 years (or longer for audits).

  • Tax Credits: Explore credits like the R&D credit (Form 6765) or Work Opportunity Tax Credit if applicable.

Step 4: State-Specific Requirements

Since you didn’t specify your state, I’ll provide an example for California (a common startup hub). Adjust based on your state:

  • California Form 100: Corporation Franchise or Income Tax Return

    • Purpose: Reports income and pays the $800 minimum franchise tax (waived for the first year if newly incorporated) plus 8.84% income tax.

    • Deadline: April 15, 2025 (or October 15, 2025 with extension via Form FTB 3539).

    • Link: Form 100

  • Delaware Franchise Tax (if incorporated in Delaware):

    • Purpose: Annual tax based on authorized shares or assumed par value.

    • Deadline: March 1, 2025 (estimated payments due quarterly: March 1, June 1, September 1, December 1).

    • Link: Delaware Franchise Tax

  • Check Your State: Visit your state’s tax or revenue department website (e.g., California FTB, New York Tax).

Step 5: Key Dates Recap (2025 Calendar Year)

  • March 21, 2025: BOI Report due (for pre-2024 C-Corps).

  • April 15, 2025: Form 1120 due, 1st quarter estimated taxes, Form 7004 for extension.

  • June 16, 2025: 2nd quarter estimated taxes.

  • September 15, 2025: 3rd quarter estimated taxes.

  • October 15, 2025: Extended Form 1120 deadline.

  • December 15, 2025: 4th quarter estimated taxes.

  • January 31, 2026: W-2s, 1099s, Form 940, ACA 1095-C to employees.

  • February 28, 2026: Form 3921 (paper), ACA 1094-C/1095-C (paper).

  • March 31, 2026: Form 3921 (e-file), ACA 1094-C/1095-C (e-file).