For tax year 2025, the due date for filing Form 1120S is March 15, 2026, according to the IRS [Revenue Procedure 2024-40](https://www.irs.gov/pub/irs-drop/rp-24-40.pdf). However, if the corporation operates on a fiscal year other than the calendar year, the due date is the 15th day of the 3rd month after the end of the tax year. An automatic six-month extension is available by filing Form 7004 and paying any expected tax due.
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