Between individual returns, business entities, and quarterly estimates, it is easy to lose track of a deadline until a penalty notice shows up. Here is every date that matters for the 2025 tax year, filed in 2026.
March 16, 2026 is the deadline for calendar-year S-corporations and partnerships to file Form 1120-S or 1065, or to request a six-month extension. April 15, 2026 covers individual Form 1040 returns, C-corporation Form 1120, and the first 2026 quarterly estimate.
Extensions push individual and C-corp deadlines to October 15, 2026, and S-corp/partnership extensions to September 15, 2026 — but an extension to file is never an extension to pay. Quarterly estimates for individuals and businesses paying as they go are due April 15, June 15, September 15, and January 15 of the following year.
We send clients a reminder ahead of each date on this calendar as part of year-round support, so nothing depends on remembering it yourself.
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