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Essential September 2025 Tax Deadlines for Businesses

As we approach September 2025, businesses must remain vigilant about key tax deadlines that can significantly impact financial planning and compliance. Among these are the crucial filings and payments due for S corporations, partnerships, and corporations, as well as payroll tax obligations. Failing to meet these deadlines can result in penalties, so being prepared is essential.

September 15 - S Corporations
Businesses operating as S corporations face a September 15 deadline to file 2024 calendar year income tax returns (Form 1120-S) if they have previously secured an automatic 6-month extension. It’s imperative to distribute a copy of Schedule K-1 (Form 1120-S) or a substitute along with, if applicable, Schedule K-3 (Form 1120-S) to each shareholder.Image 2

September 15 - Corporations
Corporations utilizing the calendar year system must deposit their third installment of estimated income tax for 2025 by September 15. This payment is critical for maintaining cash flow and avoiding interest charges on underpaid taxes. Aligning these payments with broader financial strategies can enhance organizational fiscal health.Image 3

September 15 - Partnerships
For partnerships holding a 6-month extension, September 15 marks the due date to file 2024 returns (Form 1065). Partners must receive their respective Schedule K-1 (Form 1065) or substitutes by this date to ensure transparency and compliance.Image 1

September 15 - Social Security, Medicare, and Withheld Income Tax
Employers adhering to the monthly deposit rules need to deposit Social Security, Medicare, and withheld income tax for August 2025 by September 15. If nonpayroll withholding applies, the same deadline holds, maintaining compliance with federal requirements and impacting your workforce’s economic well-being.

Weekends & Holidays
It is also worth noting, if any due dates fall on a Saturday, Sunday, or legal holiday, they automatically move to the next business day that isn't a legal holiday, allowing businesses some flexibility in these circumstances.

Disaster Area Extensions
In situations where a geographic area is declared a disaster area, the IRS provides extensions. For the most current information on designated disaster areas and related filing extensions, visit the FEMA and IRS websites.

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