US tax filing deadlines (IRS)
The dates that matter for a federal individual return, what an extension actually extends, and the distinction that costs people money — filing late and paying late are two different penalties.
What the rule is
A federal individual income tax return is due on April 15 following the close of the calendar tax year. An automatic six-month extension to October 15 is available on request, without needing a reason.
Who it applies to
Individuals filing a federal return. State deadlines are set separately and several do not match the federal date — a state return is a separate obligation with its own calendar.
The distinction that costs money
| Obligation | Original date | With an extension |
|---|---|---|
| File the return | April 15 | October 15 |
| Pay the tax owed | April 15 | April 15 — unchanged |
| Interest on unpaid tax | Runs from April 15 | Runs from April 15 |
Filing late and paying late are two separate failures with two separate penalties. An extension removes the first and does nothing about the second, which is why an extension filed alongside no payment is a common and expensive misunderstanding.
Common mistakes
- Treating an extension as more time to pay. It is not. Estimate what is owed and pay it by April 15.
- Forgetting the state return. It has its own deadline, and it is often not April 15.
- Assuming the date never moves. When April 15 falls on a weekend or a holiday the deadline shifts. Confirm the date for the year you are filing.
What this rests on
- 1Form 1040 Instructions — When To FileIRSin force from 1 January 2026
- 2Extension of Time To File Your Tax Return — Form 4868IRSin force from 1 January 2026
Locators, not document titles. A citation naming the act without naming the section is not one anybody can check.
Where this fits
- The filing calendarWhere filing deadlines is covered in depth
- Coverage for United StatesIts disclosed limitation: Federal individual income; state income tax is answered from sources, not calculated.
- Australia tax agent client onboarding checklist 2026The same topic in AU
- Canada corporate year-end tax checklist 2026The same topic in CA
- UK MTD quarterly update review checklist 2026The same topic in UK
Related guides, and why
- Guide
Australia tax agent client onboarding checklist 2026
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UK MTD quarterly update review checklist 2026
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