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The Smarter Startup
September 15, 2025

Key Q4 2025 Tax Deadlines for Startups

By preparing for these Q4 tax deadlines now, your startup can avoid costly missteps and stay focused on achieving year-end goals with confidence and clarity.

Staying on top of tax deadlines is critical for your startup’s financial health. From estimated tax payments to R&D Tax Credit filings that can unlock valuable savings, these dates directly influence cash flow, investor confidence, and your ability to close the year on strong financial footing. This guide outlines the most important Q4 2025 deadlines, explains why they matter, and shows how to stay proactive.

Also see Burkland’s roundup of important 2025 tax deadlines for startups. It includes federal filing dates as well as key deadlines for San Francisco, New York, and Seattle throughout the year.

Burkland can assist you with preparing and submitting for all of these upcoming deadlines.

Q4 Tax Deadlines

October 15

  • Business Income Tax Returns
    • C Corporations (Form 1120) with a calendar year-end must also file by October 15, 2025, if they requested an extension.
  • R&D Tax Credit Filed
    • Especially if your company plans to utilize the Payroll Tax benefit with the R&D Tax Credit filing, the deadline for all calendar year C Corporations will be October 15, 2025.

Late October

  • Sales and Use Tax Returns (Monthly, Quarterly, Semiannual): Depending on your filing frequency, sales and use tax returns may be due between October 20 and October 31.
    • Why It Matters: These filings cover taxable sales activities for different periods. Missing your due date based on your assigned frequency can result in penalties and interest.
    • Steps to Take: Confirm your filing frequency with your state tax agency and submit your return and payment accordingly.

November 15

  • Exempt Organizations (Form 990 series): Calendar year exempt Organizations that filed an extension must submit their returns by this date.

November & December

  • Monthly Sales and Use Tax Returns (November 20–31 and December 20–30): Monthly filers must submit returns for November and December during these windows.
    • Why It Matters: Monthly deadlines are easy to miss but critical for avoiding late fees.
    • Steps to Take: Review your November and December sales data and submit each return during the appropriate state filing window.

    December 1

    • Delaware Quarterly Estimated Franchise Tax: Pay the fourth installment of Delaware’s franchise tax if your startup is incorporated there.
      • Why It Matters: Ensures compliance with state regulations and prevents penalties.
      • Steps to Take: Log into Delaware’s online tax portal and submit your estimated payment, if required.

    December 15

    • Federal Quarterly Estimated Taxes (Q4): Make your fourth estimated federal tax payment for 2025.
      • Why It Matters: Paying quarterly helps avoid underpayment penalties and interest charges.
      • Steps to Take: If you are uncertain about your estimated tax payments or anticipate larger income in 2025, reach out to your tax preparer or Burkland. Payment submission is often through the IRS online payment portal.
    • State Quarterly Estimated Taxes (CA, NY, etc.): Pay Q4 estimated state taxes if operating in states requiring quarterly payments.
      • Why It Matters: Similar to federal rules, state authorities assess penalties for late payments.
      • Steps to Take: When Burkland completes your income tax returns, we provide estimated tax payment schedules. If you are uncertain about your estimated tax payments or anticipate larger income in 2025, reach out to your tax preparer or Burkland. Burkland can guide you on payment submission, which differs by state.

    Q4 Tax Planning Tips for Startups

    1. Optimize Business Tax Strategies: Consider purchasing equipment to take advantage of the Section 179 deduction, allowing immediate expensing of qualifying property.
    2. Prepare for Tax Filing Season: Organize tax records, including W-2s, obtain domestic vendor W-9s and international vendor W-8BEN/W-8BEN-Es, 1099s, and receipts for deductible expenses. This ensures accurate reporting and reduces the risk of errors.
    3. Review Eligibility: Confirm eligibility for new deductions and credits introduced by the OBBBA.
    4. Quarterly Payments: Ensure timely payment of Q4 estimated taxes by January 15, 2026

    Need help navigating Q4 tax deadlines or maximizing your credits? Burkland’s startup tax experts are here to guide you every step of the way. Contact us to streamline compliance and stay focused on growing your business.