800+ Venture-Funded Startups Across the USA Trust Burkland
415-651-5319
The Smarter Startup
June 24, 2025

Key Q3 2025 Tax Deadlines for Startups

By preparing for these Q3 tax deadlines now, your startup can avoid costly missteps and stay focused on achieving year-end goals with confidence and clarity.

As the second half of 2025 gets underway, Q3 presents several important tax deadlines that startups can’t afford to overlook. From estimated tax payments to annual reporting for benefits plans, staying on top of these filings is essential for compliance, cash flow management, and strategic planning. Below is your startup’s guide to the most critical Q3 tax deadlines, why they matter, and how to prepare.

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.

Q3 Tax Deadlines

Late July

  • Sales and Use Tax Returns (Monthly, Quarterly, Semiannual): Depending on your filing frequency, sales and use tax returns may be due between July 20 and July 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.

July 31

  • Annual Return/Report of Employee Benefit Plan (Form 5500): File this return for 401(k) and other benefit plans.
    • Why It Matters: Ensures ERISA compliance and avoids significant Department of Labor penalties.
    • Steps to Take: Coordinate with your plan administrator to gather plan information and file Form 5500.

August & September

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

September 1

  • Delaware Quarterly Estimated Franchise Tax: Pay the third 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.

September 15: Major Tax Filing Deadline

  • Federal Quarterly Estimated Taxes (Q3): Make your third 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 Q3 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.
  • S-Corp and Partnership Tax Returns with Extensions: If your startup filed for an extension in March, this is your new filing deadline.
    • Why It Matters: Failure to file by this date may void your extension and incur late filing penalties.
    • Steps to Take: File your return.

September 30: Last Day to File Tax Return for R&D Credit Monetization in Q4

  • September 30 is the deadline to file amended or original income tax returns in order to apply the R&D tax credit toward Q4 payroll tax liabilities. (Note, the calendar-year tax deadline remains October 15th).
    • Why It Matters: Missing this deadline delays credit monetization by at least one quarter, potentially deferring significant cash flow benefits.
    • Steps to Take: If you’re already working with us on the R&D credit, Burkland is taking steps to ensure your return is filed in time to monetize the credit in Q4. If you have any outstanding documents or action items, now is the time to send them so we can meet this deadline. Not sure where things stand? Reach out — we’re happy to confirm your status.

Q3 Tax Planning Tips for Startups

  1. Update Financial Projections: Align Q3 tax payments with the latest revenue forecasts.
  2. Check Extension Status: If you filed any tax extensions earlier in the year, track their respective deadlines now.
  3. Audit Your Compliance: Perform a mid-year compliance review to ensure accurate filings and minimize risk.

 

Need help navigating Q3 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.