Key Takeaways
- Individual returns (Form 1040): due April 15 for calendar-year taxpayers
- Partnerships (1065) and S-Corps (1120-S): due March 15
- Automatic 6-month extension available by filing Form 4868 (extends to October 15)
- Extension extends time to file only — taxes owed must still be paid by April 15
- If the due date falls on a weekend or holiday, the deadline moves to the next business day
The General Due Date Rule
The IRS defines the tax return due date as the 15th day of the 4th month after the end of your tax year. Since 99% of individual taxpayers use the calendar year (ending December 31), this translates to April 15 of the following year. This is the date by which you must either file your return or request an extension.
For partnerships and S-Corporations, the deadline is earlier: March 15 (the 15th day of the 3rd month). This is because these entities need to issue K-1 forms to their partners/shareholders in time for those individuals to prepare their own returns.
Extensions: More Time to File, Not to Pay
Filing Form 4868 grants an automatic 6-month extension for individuals, pushing the deadline to October 15. However, this is an extension of time to file, not an extension of time to pay. If you owe taxes, you must estimate and pay them by April 15 to avoid interest and late payment penalties.
Many taxpayers misunderstand this distinction and wait until October to both file and pay. The result is interest charges dating back to April 15, plus potential late payment penalties.
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