5 Critical Tax Deadlines You Can’t Miss in 2026

“Five on Fridays” is back for 2026. As we kick off the new year, it is vital to get your financial calendar organized immediately. Missing a tax deadline can result in unnecessary penalties and interest that compound quickly.

In this week’s video, Managing Attorney Mark Milton outlines the five critical tax deadlines you need to mark on your calendar right now to ensure a smooth tax season.

1. January 15th: 4th Quarter Estimated Tax Payments

For business owners and independent contractors, the tax year isn’t quite over yet. January 15th is the deadline for your 4th Quarter estimated tax payment for the 2025 tax year.

If you suspect you will owe taxes for 2025 or if you didn’t have enough withholding throughout the year, you must make a payment by this date. Failing to do so often triggers the “underpayment of estimated tax” penalty when you file your return in April.

2. January 26th: IRS Filing Season Opens

The IRS has announced that January 26th is the official start of the filing season. This is the first day the IRS will begin accepting and processing electronic and paper returns. If you are expecting a refund and have your documents ready, this is the earliest you can submit your return.

3. February 2nd: Deadline for W-2s and 1099s

February 2nd is a major deadline for employers and financial institutions. This is the date by which they must mail out Form W-2s to employees and Form 1099s to contractors.

For taxpayers, this means you should be keeping a close eye on your mailbox (and email) starting in early February. You cannot file an accurate return until you have received all these documents.

4. March 16th: Entity Return Deadline

If you own a business, this date is critical. March 16th is the filing deadline for most entity returns, specifically Partnerships (Form 1065) and S-Corporations (Form 1120-S).

If you cannot file by this date, you must file an extension. Missing this deadline is expensive—the penalty for late filing a partnership or S-Corp return is roughly $220 per partner/shareholder, per month. Do not let this one slip by!

5. April 15th: The Individual Filing Deadline

The big one remains unchanged. April 15th is the deadline to file your individual income tax returns or to file an extension.

Mark reiterates his “Golden Rule” of tax extensions: An extension to file is NOT an extension to pay. If you file an extension, it gives you until October 15th to submit your paperwork, but if you owe money, that payment is still due on April 15th. To avoid interest and penalties, you must make an estimated payment with your extension.

Stay Ahead of the Calendar

Managing these dates can be overwhelming, especially for business owners juggling multiple deadlines. At Milton Law Group, we specialize in keeping you compliant and penalty-free.

If you have questions about your estimated payments or need help with business tax planning for 2026, contact Milton Law Group today.