Form 1065 and 1120-S Filing Deadlines and Late Filing Penalties

Updated September 12, 2026. Covers calendar-year 2025 returns filed in 2026.

For calendar-year 2025 partnership and S corporation returns, the regular federal filing deadline was March 16, 2026. A timely, valid extension generally moves the deadline to September 15, 2026. The March date shifts because March 15 falls on a Sunday. Fiscal-year businesses and taxpayers covered by special relief may have different deadlines. See the IRS instructions for Form 1065 and Form 1120-S.

Missing the deadline can create a substantial penalty even when the business owes no federal income tax. Before calculating exposure, establish the return year, whether an extension was valid, and how many people held ownership interests during the year.

When are partnership and S corporation returns due?

For a fiscal-year entity, the general deadline is the 15th day of the third month after its tax year ends, subject to applicable exceptions. Do not use the calendar-year dates without confirming the business’s tax year. IRS Form 1065 instructions, IRS Form 1120-S instructions.

How does Form 7004 extend the deadline?

Most partnerships and S corporations use Form 7004 to request an automatic six-month filing extension. It generally must be filed by the original return deadline. Keep proof of timely filing and, for an electronic submission, the acceptance acknowledgment.

A business extension does not extend an owner’s individual return. An owner’s personal extension likewise does not extend the business return. Filing Form 7004 also does not extend the time to pay tax that is due. IRS Form 7004 instructions.

September 15 is normally the end of the regular extension for a calendar-year entity. However, an IRS disaster postponement or other applicable special relief can change the deadline. Check the relief announcement’s covered taxpayers, locations, and filing periods before relying on a later date. IRS disaster tax relief.

How much is the late-filing penalty?

For returns required to be filed in 2026, the basic federal late-filing penalty is generally $255 per partner or shareholder for each month or part of a month, for up to 12 months. Count everyone who was a partner or shareholder at any time during the tax year, rather than just the owners remaining at year-end. The amount is adjusted for inflation, so use the rate applicable to the return’s required filing year. IRS failure-to-file penalty guidance.

For the basic penalty, the calculation is:

$255 × number of partners or shareholders × months or partial months late, up to 12.

These examples exclude other penalties and assume no relief applies. An S corporation owing tax can face additional tax-based penalties. Missing or incorrect Schedules K-1 can also create separate exposure. IRS Form 1120-S instructions.

Does October 1 start a second penalty month?

No. Penalty months are measured from the applicable due date, rather than by counting calendar months touched by the delay.

For a return validly extended to September 15, 2026, the first penalty month runs September 16 through October 15. Filing on October 2 falls within that first period. With four owners, the basic penalty would therefore be $1,020, assuming no special relief or other penalties. Filing on October 16 enters a second penalty month and increases that amount to $2,040. These examples apply the IRS’s due-date-based method for counting penalty months. IRS penalty computation guidance.

Can a penalty apply when no tax is owed?

Yes. The partnership filing penalty concerns the required information return and can apply even without entity-level income tax. An incomplete return can also trigger a penalty. IRS Form 1065 instructions.

S corporations generally pass income and other tax items through to shareholders, but some owe entity-level taxes, including certain built-in gains taxes. Saying that no tax is ever due with Form 1120-S would be inaccurate. IRS Form 1120-S instructions.

What should you do after missing the deadline?

1. Verify the filing history. Locate the return, extension, electronic acceptance records, and any IRS notices.
2. Finish the required filing. Reconcile the books and prepare complete returns and owner schedules promptly.
3. Check the penalty calculation. Compare the IRS’s due date, owner count, applicable rate, and number of late months against the records.
4. Evaluate relief. Identify the applicable relief provision and gather the evidence it requires.

Keep a dated chronology of what prevented filing and what steps the business took to resolve the problem. If a notice has arrived, preserve it and track its response deadline. For assistance with overdue filings, see our unfiled tax returns service.

Can the IRS remove the penalty?

Depending on the facts, reasonable cause may support relief. Certain small partnerships may qualify under Revenue Procedure 84-35. Having ten or fewer partners is only one condition: partner eligibility, consistent proportional allocations, timely owner reporting, and the other IRS requirements must also be checked. This partnership provision is not an S corporation exemption. IRS CP162A notice guidance.

Administrative relief may also apply. The IRS describes a transition beginning in summer 2026 from First Time Abate to Automatic Exemption from Penalty for eligible returns, including Forms 1065 and 1120-S. Eligibility depends on the applicable period and compliance history. If a penalty was assessed, check whether relief was applied or needs to be requested. IRS administrative penalty relief.

For help evaluating a notice and supporting a request, see our tax penalty abatement service.

Colorado DR 0106 has a different deadline

The federal September deadline should not be confused with Colorado’s filing schedule. For calendar-year 2025, Colorado DR 0106 is generally due April 15, 2026, with an automatic six-month filing extension to October 15, 2026. The state extension does not extend the payment deadline. Colorado’s 2025 DR 0106 instructions.

See our separate discussion of Colorado partnership and S corporation filing requirements for the state return.

Help with a partnership or S corporation return

If your business needs a return prepared, review our Form 1065 partnership tax services or Form 1120-S S corporation tax services. If you received a penalty notice, bring the notice, extension confirmation, filed return, and ownership history to a consultation so the filing obligation and potential relief can be evaluated together.