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.
Q3 Tax Deadlines
July 31: Don’t Miss These Three Major Filings
- Quarterly Sales and Use Tax Filing: Report and remit Q2 sales and use tax if your startup sells taxable goods or services.
- Why It Matters: Late filings can result in penalties, interest, or even audits.
- Steps to Take: Use state portals to submit your sales data and tax payment by the due date.
- 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.
September 1: Franchise Tax Installment
- 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.
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: Calculate estimated taxes based on projected annual income and submit payment via 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: Use your state tax portal to calculate and submit payments.
- 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: Ensure all required documents and K-1 forms are completed and submitted.
September 30: Trust Tax Filing Deadline
- Form 1041 Extended Return: Extended due date for fiduciary income tax returns for trusts.
- Why It Matters: Applies to startups managing trusts or grantor trusts as part of a legal or investment structure.
- Steps to Take: Confirm all trust-related income and distributions are properly accounted for before filing Form 1041.
Q3 Tax Planning Tips for Startups
- Update Financial Projections: Align Q3 tax payments with the latest revenue forecasts.
- Check Extension Status: If you filed any tax extensions earlier in the year, track their respective deadlines now.
- 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.