September 15, 2025 IRS Deadlines: Tax-Saving Strategies for Business Owners
September 15, 2025, is more than a date on the calendar. It’s a critical day for business owners to manage taxes efficiently and protect cash flow.
This day marks two major obligations:
-
Your third-quarter estimated tax payment (individuals and business owners)
-
Final extended filings for S-corporations (Form 1120-S) and partnerships (Form 1065)
Missing deadlines or miscalculating payments can trigger penalties, interest, and lost tax-saving opportunities. A well-planned approach today keeps more money in your business.
Third-Quarter Estimated Taxes: Calculating and Paying
The third payment for the 2025 tax year is due September 15, 2025.
Quarterly dates for 2025 are:
-
April 15
-
June 16
-
September 15
-
January 15, 2026
If the date falls on a weekend or holiday, the IRS moves it to the next business day.
Who Should Pay Q3 Estimated Taxes?
Pay if both conditions apply:
-
You expect to owe $1,000 or more after credits and withholding.
-
Your withholding and estimates are less than 90% of this year’s tax, or 100% of last year’s tax (110% if last year’s AGI was above the high-income threshold).
This is the safe harbor standard, preventing underpayment penalties even if your final bill is higher.
How to Estimate Your Q3 Payment
-
Open last year’s tax return and find “Total Tax.”
-
Use 100% or 110% of that number depending on your income level.
-
Divide by 4.
-
Subtract Q1 and Q2 payments.
-
Pay the difference for Q3.
For more precision, use the Form 1040-ES worksheet. Adjust the next quarter if your income changes.
Payment Methods
-
IRS Direct Pay: Bank account transfers for individuals.
-
EFTPS: Required for many business payments.
Keep the confirmation number for your records.
Extended S-Corporation Filings (Form 1120-S)
S-corporations that filed a Form 7004 extension must submit their 2024 calendar-year return by September 15, 2025.
-
Furnish Schedule K-1 to each shareholder.
-
Include K-2/K-3 if international shareholder information is requested by the one-month date (August 15, 2025).
-
Payroll and employment tax deposits remain on their regular schedules—extension doesn’t delay payments.
S-Corp Tax-Saving Tactics
-
Retirement contributions: Fund a 401(k) or defined benefit plan for owners. This reduces taxable income and strengthens your retirement.
-
Officer compensation: Balance salary vs. distributions to optimize payroll taxes.
-
Health plans and fringe benefits: Leverage Triple Tax Advantage Self-Employed Health Insurance Reimbursement strategies.
-
Risk management: Explore Power of Private Insurance and captive insurance solutions to shift risk and reduce taxes.
Extended Partnership Filings (Form 1065)
Partnerships on extension also face September 15, 2025 as the final filing date for 2024 calendar-year returns.
-
Furnish Schedule K-1 to each partner.
-
Include K-2/K-3 if requested by the one-month date.
Partnership Tax-Saving Tactics
-
Guaranteed payments: Structure partner compensation efficiently to manage self-employment taxes.
-
Business deductions: Deduct business expenses like home office, heavy vehicles, or business travel. See Heavy Vehicle & Home Office Tax Deductions for details.
-
Retirement contributions: Maximize SEP-IRA or Solo 401(k) contributions to reduce taxable income.
-
Consider corporate structures to optimize tax liability if your partnership has high growth potential.
C-Corporation Edge Cases
C-corporations with a fiscal year ending June 30 file Form 1120 by the 15th day of the third month after year-end. For many, this also falls in September.
Tax-Saving Tactics for C-Corps
-
Charitable contributions: Deductible up to 10% of taxable income.
-
Qualified business income planning: For certain hybrid structures, explore deductions.
-
Risk management: Self-Insurance Guide can help manage liabilities and optimize taxes.
Safe Harbor Planning
Safe harbor reduces penalties:
-
90% of current-year tax, or
-
100%/110% of prior-year tax depending on AGI.
Even if cash is tight, you can:
-
Increase workplace withholding.
-
True-up by January 15, 2026.
-
Retirees can use IRA or pension withholding; the IRS treats it as evenly paid through the year.
Quick Checklist for Business Owners
-
✅ Confirm your safe-harbor target
-
✅ Pay Q3 via Direct Pay or EFTPS
-
✅ Finish S-Corp or partnership extended filings
-
✅ Deliver K-1s and K-2/K-3 if applicable
-
✅ Confirm C-Corp September filing if applicable
-
✅ Explore tax-saving tactics: retirement contributions, deductions, and insurance strategies
Where a Tax Advisor Adds Value
A professional can:
-
Confirm Q3 estimated tax and safe-harbor calculations
-
Review K-2/K-3 requirements and deadlines
-
Optimize S-corp payroll, officer compensation, and retirement funding
-
Plan for year-end business transactions: sales, partner changes, or entity restructuring
Additional reading:
FAQ for Business Owners
Q: What exactly is due September 15, 2025?
A: Q3 estimated taxes, S-Corp 1120-S (extended), and partnership 1065 (extended) with K-1s.
Q: How do I pay Q3 estimated taxes?
A: Use IRS Direct Pay or EFTPS. Keep your confirmation.
Q: What is safe harbor?
A: Avoid penalties by paying 90% of this year’s tax, 100% of last year’s tax, or 110% if prior-year AGI exceeds the high-income threshold.
Q: Do I need to send K-3s?
A: Only if requested by a shareholder or partner by the one-month date (August 15, 2025).
Q: What if I miss September 15?
A: Pay as soon as possible. Penalties and interest can apply. Meeting safe harbor limits can reduce penalties.
Q: What if cash is tight today?
A: Increase workplace withholding for the rest of the year, or use IRA/pension withholding.
Block one hour today.
-
Send your Q3 payment.
-
File your extended 1120-S or 1065 and deliver K-1s.
-
Add a calendar hold for January 15, 2026, to true-up payments or finalize year-end strategies.
A proactive tax strategy today ensures more money stays in your business and reduces unexpected penalties.
At Provident CPAs, we specialize in helping clients adapt to changing economic conditions. Whether you’re a business owner or an individual looking to optimize your tax strategy, our team is here to guide you through the complexities of today’s tax landscape. Contact us today to learn more about how we can help you achieve financial independence, even in the face of economic uncertainty.