Calendar of Important Dates in 2026

The new year has begun, and tax season is in full swing!  There are important dates and deadlines to consider ensuring timely tax filing and payments throughout the year, while also planning for government holidays that may cause deadline adjustments.  If you have any questions, please do not hesitate to reach out to your ATLAS or CMMS office directly; or contact us through our website, here.

 

January 1, 2026
— New Year’s Day — ATLAS and CMMS offices closed in observance.
— IRS Legal Holiday.
— General Enrollment Period begins (for Original Medicare, Part A and/or Part B, if you missed your Initial Enrollment Period (IEP) and runs from January 1 through March 31, 2026.  Coverage starts on July 1, 2026.
— Medicare Advantage Open Enrollment Period begins (for those already in Medicare Advantage — to switch plans or return to Original Medicare) and runs from January 1 through March 31, 2026.

 

January 15, 2026
— 2025 4th Quarter Estimated Tax Payments due.
— IRS will begin accepting BUSINESS tax returns via e-filing.

 

January 19, 2026
— IRS Legal Holiday – Birthday of Martin Luther King, Jr. / Inauguration Day.

 

January 26-30, 2026
— IRS marks this week as the “official” start of tax season, and will begin accepting INDIVIDUAL tax returns via e-filing.

 

February 2, 2026
— 2025 1099s Filing due date, and forms due to recipients.
— 2025 W-3/W-2s Filing due date, and forms due to recipients.
— 2025 4th Quarter 941 and 2025 940 Filing due date (Annual Payroll Reconciliation returns.)

 

February 16, 2026
— IRS Legal Holiday – Washington’s Birthday.

 

March 2, 2026
— 2025 Payment due date for Qualified Farmer returns, and Qualified Fishers returns.

 

March 16, 2026
— 2025 1065 (Partnership) Tax returns due; or extension filing due if needed.
— 2025 1120-S (S-Corporation) Tax returns due; or extension filing due if needed.
— 2025 1065 and 1120-S tax payment due date, if business entity has filed for PTET.
** An extension of time to file your tax returns, does not provide you with an extension of time to pay your tax balance due.

 

April 15, 2026
— Final date to make IRA Contributions for tax year 2025.
— 2025 1120 (Corporation) Tax returns due; or extension filing due if needed.
— 2025 1040 (Individual/Personal) Tax returns due; or extension filing due if needed.
— 2025 1041 (Fiduciary/Estate/Trust) Tax returns due; or extension filing due if needed (this is based on an estate or trust with a calendar year end – fiscal year end estates and trusts are due by the 15th day of the 4th month following the close of the entity’s tax year.)
— 2025 709 (Gift) Tax returns due; or extension filing due if needed.
— 2025 FBAR (Foreign Bank and Financial Accounts) Report due with your individual returns; or if an extension is needed, your FBAR must be extended with your 1040 returns – failure to file timely penalties are substantial.
— 2025 tax payment due date for 1120, 1040, and 1041.
** An extension of time to file your tax returns, does not provide you with an extension of time to pay your tax balance due.
— 2026 1st Quarter Estimated Tax Payments due.

 

April 16, 2026
— IRS Legal Holiday – District of Columbia Emancipation Day.

 

April 30, 2026
— 2026 1st Quarter 941 Payroll Tax Reports filing due date.

 

May 15, 2026
— 2025 990 (Non-profit/Exempt Organizations) Tax returns due; or extension filing due if needed.  This is based on a calendar year end – fiscal year end organizations are due by the 15th day of the 5th month following the close of the organization’s accounting period.

 

May 25, 2026
— Memorial Day — ATLAS offices closed in observance.
— IRS Legal Holiday.

 

June 15, 2026
— 2026 2nd Quarter Estimated Tax Payments due.

 

June 19, 2026
— IRS Legal Holiday – Juneteenth National Independence Day.

 

July 3, 2026
— Independence Day (observed) — ATLAS and CMMS offices closed in observance.
— IRS Legal Holiday.

 

July 31, 2026
— 2026 2nd Quarter 941 Payroll Tax Reports filing due date.

 

September 7, 2026
— Labor Day — ATLAS and CMMS office closed in observance.
— IRS Legal Holiday.

 

September 15, 2026
— Extended due date for 2025 1065 (Partnership) Tax returns.
— Extended due date for 2025 1120-S (S-Corporation) Tax returns.
— 2026 3rd Quarter Estimated Tax Payments due.

 

October 12, 2026
— IRS Legal Holiday – Indigenous Peoples’ Day (Columbus Day.)

 

October 15, 2026
— Extended due date for 2025 1120 (Corporation) Tax returns.
— Extended due date for 2025 1040 (Individual) Tax returns.
— Extended due date for 2025 1041 (Fiduciary/Estate/Trust) Tax returns (if calendar year.)
— Extended due date for 2025 709 (Gift) Tax returns.
— Extended due date for 2025 FBAR – must be filed with 1040, if required.

 

November 2, 2026
— 2026 3rd Quarter 941 Payroll Tax Report filing due date.

 

November 11, 2026
— IRS Legal Holiday – Veterans Day.

 

November 16, 2026
— Extended due date for 2025 990 (Non-profit/Exempt Organizations) Tax returns, if the returns are on a calendar year.

 

November 26, 2026
— IRS Legal Holiday – Thanksgiving Day.

 

November 26 and 27, 2026
— Thanksgiving Break — ATLAS and CMMS offices closed in observance.

 

December 24, 2026
— ATLAS and CMMS offices closed in observance of the holiday season.

 

December 25, 2026
— IRS Legal Holiday – Christmas Day.
— ATLAS and CMMS offices closed in observance of the holiday season.

 

January 1, 2027
— ATLAS and CMMS offices closed in observance of the New Year holiday.

 

*** SALES TAX Filing due dates are subject to the jurisdiction in which filing is required.  If monthly, sales tax is due by the 20th day of the month following the sales tax period;  otherwise, if quarterly, by the 20th day of the month following the close of the quarter;  or, if annually, by the 20th day of January for the complete prior year.

 

If you have any questions about these important dates, please reach out to your ATLAS or CMMS office directly; or contact us through our website, here.