Business Tax Deadlines 2026: S-Corp, Partnership, and C-Corp Filing Calendar

S-Corporation and Partnership Deadlines (Form 1120-S and Form 1065)

Calendar-year S corporations and partnerships share the same filing deadline. Both are pass-through entities - income and losses flow to owners' personal returns. This is why both are due one month before the individual Form 1040 deadline: owners need the Schedule K-1 to complete their personal returns.

March 15 is the statutory due date for S-Corp and partnership returns. In 2026, March 15 falls on a Sunday, so the deadline shifts to the next business day: Monday, March 16, 2026.

S-Corp income, losses, credits, and deductions pass through to each shareholder's Form 1040 via Schedule K-1. The S-Corp must file Form 1120-S before shareholders can complete their individual returns. Filing on extension means shareholders may also need to extend their personal returns.

Multi-member LLCs that have elected partnership tax treatment file Form 1065 - not Form 1120-S. Single-member LLCs treated as disregarded entities file Schedule C with the owner's Form 1040, which is due April 15.

C-Corporation Deadlines (Form 1120)

C corporations file Form 1120 by the 15th day of the fourth month after the close of the tax year. For calendar-year C corporations, that is April 15. C corporations are separate taxpaying entities - they do not pass income through to shareholders.

C-Corp estimated tax quarters differ from individual estimated tax quarters. Individuals pay estimated tax in April, June, September, and January. C corporations pay in April, June, September, and December - not January. Each installment is 25% of the corporation's estimated annual tax liability.

C corporations with less than $500 in expected annual tax liability are generally not required to make estimated payments. Corporations that fail to make adequate estimated payments may owe an underpayment penalty under IRC section 6655.

Sole Proprietor and Single-Member LLC Deadlines

Sole proprietors and single-member LLCs treated as disregarded entities report business income on Schedule C, which is filed with Form 1040. The deadline is April 15, 2026. If you need more time to file, use Form 4868 to extend to October 15, 2026. Quarterly estimated taxes are due April 15, June 15, September 15, 2026, and January 15, 2027. For the full self-employed filing calendar including state deadlines and quarterly payment worksheets, see Self-Employed Tax Deadlines.

Employment Tax Deadlines for Businesses

Businesses with employees must file employment tax returns and deposit payroll taxes on a separate schedule from income tax returns. Missing these deadlines triggers the Trust Fund Recovery Penalty, which the IRS can assess personally against responsible parties.

Payroll tax deposit schedules (semi-weekly or monthly) are separate from these quarterly return due dates. The deposit schedule is determined by the business's lookback period tax liability and is assigned at the start of each calendar year. The Form 941 quarterly return reconciles those deposits.

Businesses with annual Form 941 liability below $1,000 may qualify to file Form 944 annually instead of quarterly. Check your IRS notice or contact the IRS to confirm your filing frequency assignment.

How to File Form 7004 for a Business Tax Extension

Form 7004 grants an automatic 6-month extension of time to file most business income tax returns. No signature is required and the IRS does not need to approve the extension - it is automatic when properly filed by the original due date.

1. Determine your entity type and the correct form code. Form 7004 covers multiple return types. S corporations use the Form 1120-S code. Partnerships use the Form 1065 code. C corporations use the Form 1120 code. Each code has its own line on Form 7004.
2. Estimate the tax owed and make payment by the original due date. Form 7004 extends the filing deadline only. Any tax owed is still due on the original due date. Estimate your tax liability and pay as much as possible by March 16 (S-Corp/partnership) or April 15 (C-Corp). Underpayment triggers interest and the failure-to-pay penalty.
3. File Form 7004 electronically by the original due date. File Form 7004 through IRS e-file by March 16, 2026 for S corporations and partnerships, or by April 15, 2026 for C corporations. Paper filing is also permitted but electronic filing is faster and provides confirmation.
4. File the actual return by the extended deadline. With a valid Form 7004 on file, file Form 1120-S or Form 1065 by September 15, 2026, or Form 1120 by October 15, 2026. Missing the extended deadline voids the extension and late filing penalties begin from the original due date.

S-Corp Late Filing Penalty: What It Actually Costs

The $255 per month rate applies to returns due after December 31, 2025 (IRS Failure to File Penalty page). Earlier years had lower per-unit rates. The penalty maxes out at 12 months per shareholder or partner position.

When the Standard Deadlines Do Not Apply

The March 16 and April 15 deadlines are for calendar-year filers only. Several situations produce different due dates.

• Fiscal-year filers use different dates - S-Corp and partnerships are due on the 15th of the third month after fiscal year end; C-Corps are due on the 15th of the fourth month after fiscal year end.
• S-Corp with built-in gains tax or excess net passive income tax owes entity-level tax - the extension buys time to file, not time to pay that liability.
• Multi-member LLCs taxed as partnerships file Form 1065, not Form 1120-S - the deadline is the same but the form and penalty calculation reference partners, not shareholders.
• Missing Form 7004 by even one day means no extension is granted and the full late-filing penalty begins accruing from the original due date.
• Businesses in federally declared disaster areas may receive automatic deadline extensions announced by the IRS - check IRS.gov/newsroom for active disaster relief notices.

Frequently Asked Questions