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Key Tax Deadlines for Businesses in September 2025

The onset of September 2025 marks crucial tax obligations for businesses, particularly S corporations, partnerships, and corporations. This month includes deadlines for filing extended returns, paying estimated taxes, and meeting payroll deposit requirements. At CPA Consulting Services, based in Manchester, Connecticut, we ensure our clients are well-prepared for these deadlines with expert guidance and personalized support.

September 15 - S Corporations
For S corporations that filed for an automatic six-month extension, September 15 is the deadline to file the 2024 calendar year income tax return (Form 1120-S) and settle any outstanding taxes. Shareholders need to receive their Schedule K-1 or a substitute version, in addition to Schedule K-3 for international considerations.Image 2

September 15 - Corporations
The same date requires calendar year corporations to deposit their third installment of estimated income tax for 2025. Timely payment helps to avoid penalties and demonstrates efficient financial management.

September 15 - Partnerships
Partnerships are also expected to file their 2024 calendar year return (Form 1065) by this date if they were granted a six-month extension. Partners must be provided with their respective Schedule K-1 and, when applicable, Schedule K-3.

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