Key September 2025 Tax Deadlines for Businesses

As the summer wanes and we transition into September, businesses must realign their focus toward impending tax deadlines. Ensuring compliance with these deadlines is not just a legal obligation but a strategic necessity for maintaining financial health. Key September deadlines, especially for S Corporations, Partnerships, and Corporations, could impact your company's fiscal outcomes significantly.

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September 15 - S Corporations

For those who filed for an automatic 6-month extension, September 15 marks the due date for submitting your 2024 calendar year tax return (Form 1120-S). Along with filing, it's crucial to provide each shareholder with their Schedule K-1 (Form 1120-S) or a substitute Schedule K-1, and if applicable, Schedule K-3. This step ensures transparency and thorough tax reporting.

September 15 - Corporations

This day also mandates the third installment of estimated income tax for calendar year corporations. Effective management of these payments aids in avoiding penalties and interest, which could otherwise strain your financial resources.

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September 15 - Partnerships

Partnerships granted a 6-month extension must also file their 2024 calendar year return (Form 1065) by this date. Supplying partners with their individualized Schedule K-1 (Form 1065) or a substitute is necessary for adhering to IRS requirements and facilitates smooth tax planning.

September 15 - Social Security, Medicare and Withheld Income Tax

Employers subject to monthly deposit rules must deposit Social Security, Medicare, and withheld income taxes for August 2025 by this deadline. This applies to nonpayroll withholdings if the monthly deposit rule is applicable.

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Weekends & Holidays

Should any due date fall on a weekend or legal holiday, anticipate it extending to the next business day, ensuring you are not penalized for a missed deadline.

Disaster Area Extensions

In circumstances where your business is located in a designated disaster area, the IRS extends certain filing deadlines. To confirm applicable extensions, visit FEMA and IRS Disaster Relief webpages.

Staying proactive about these deadlines by consulting with a tax expert or using tax software can significantly mitigate risks. Businesses should consider leveraging tax planning strategies to align with these deadlines while optimizing tax liabilities.

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