Upcoming Federal Extension Deadlines

For many taxpayers, the tax filing calendar does not end on the original March 15^th or April 15^th deadlines. If you filed a 2025 extension for yourself, an entity, or a trust/estate, the extended due date is quickly approaching.

What Does a Tax Extension Do?

A federal tax extension generally provides up to six additional months to file your tax return. This extra time allows you to gather missing information, verify your records, and reduce the risk of filing an incomplete or inaccurate return.

While an extension postpones the filing deadline, it does not postpone the payment deadline. Any unpaid balance after the original due date may continue to accrue interest and potentially penalties until paid.

Quick-Reference: Calendar Year 2025 Extended Federal Due Dates

The following dates apply to calendar-year 2025 federal tax returns that are currently on extension: 

What You Should Do Now

As you head into the September and October deadlines, confirm that your federal extensions were timely filed and make note of your remaining extended filing due dates. Then focus on closing out 2025 records (books, source documents, and open tax items), locking down Schedule K-1s and beneficiary/owner information, and coordinating the sequence of entity, owner/beneficiary, and individual filings so the reporting is consistent.

Because an extension generally extends the time to file, not the time to pay, verify whether any additional tax, interest, or penalties may still be due and plan to pay promptly to reduce added costs.

Finally, confirm state filing and payment requirements separately, since state extension rules and deadlines may differ.

2026 Estimated Tax Payments: Extensions Don’t Postpone Quarterly Obligations

Even if your 2025 tax return was extended, the extension does not postpone your 2026 estimated tax obligations. As of August 2026, the following are the remaining 2026 estimated tax payment due dates for calendar-year taxpayers:

• Individuals: September 15, 2026 and January 15, 2027
• Trusts/estates: September 15, 2026 and January 15, 2027
• C Corporations: September 15, 2026 and December 15, 2026

If you have a fiscal year filing, your quarterly estimated payment due dates will be different based on your year-end. Pass-through entities do not have federal payment obligations in most (but not all) cases but may have state payment obligations.

If you have not made any estimated payments for 2026 or believe you may be underpaid to date, it’s best to get caught up as soon as possible to mitigate underpayment penalties. If using a prior-year safe harbor, the filing of your 2025 return is the perfect time to revisit your remaining quarterly estimates.

Special Situations

While the deadlines above apply to most taxpayers, there are some exceptions. These may include military service, taxpayers living abroad, disaster relief situations, fiscal year businesses, and state income tax returns. State rules are especially important because many states have their own extension and payment requirements.

The Bottom Line

For extended calendar-year 2025 federal returns, the remaining upcoming filing dates are:

• September 15, 2026 — Partnerships (Form 1065) and S Corporations (Form 1120S)
• September 30, 2026 — Trusts and Estates (Form 1041)
• October 15, 2026 — Individuals (Form 1040) and C Corporations (Form 1120)

Taxpayers should use the month of August to close open items, confirm K-1 timing, coordinate owner/beneficiary reporting, and confirm state deadlines separately.