Tax Law and News

Key tax dates and to-do-list: October 2026

Written by Nadia Rodriguez, CPA, CTC
Published Sep 18, 2026
4 min read

October is an important month for tax accountants because it centers on the extended individual filing deadline of October 15, so the first priority is closing out those returns cleanly. Firms should be running final reviews on all extended 1040s, confirming that estimated payments, K-1 data from pass-through entities, and any late-arriving documents have been reconciled before submission.

This is also the moment to circle back with clients who still owe information, since missing the 15th can trigger penalties and interest that clients will remember at renewal time. Beyond individual returns, calendar-year C-corps and other entities with extended deadlines may also fall in this window depending on the tax year, so firms need a clear tracking system to make sure nothing slips through after the personal-return crunch ends.

Once the extension deadline passes, October is the natural pivot point toward year-end tax planning. This means reaching out proactively to review your clients’ income, capital gains and losses, retirement contributions, and any major life or business events from the year, so there’s still time to act on Roth conversions, tax-loss harvesting, entity structure changes, equipment purchases, or bunching deductions before December 31. For business clients, this is also a good time to revisit quarterly estimated tax payments (Q3 estimates were due mid-September, and Q4 planning should start now) and to flag any changes in tax law that could affect year-end strategy.

On the firm-management side, October is a good time to debrief on busy season and extension season while it’s fresh: reviewing workflow bottlenecks, staff capacity, and client communication gaps, and starting to plan staffing and technology needs for the upcoming tax season. Firms should also begin engagement-letter and pricing conversations for the next filing year, update any client organizers or portals, and make sure CPE requirements are on track since many state boards have year-end or biennial deadlines. Finally, this is a natural window to send clients a light-touch newsletter or check-in about upcoming deadlines such as 1099s and W-2s that are due in January; you want your relationships to stay warm heading into the next cycle rather than going quiet until tax season starts again.

Along the way, be sure to pay attention to these important IRS and compliance deadlines.

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In October, it is recommended that you:

Complete all extended individual and corporate returns. October 15 is the hard deadline. Prioritize 1040s for clients with complex investment income, SALT considerations, or One Big, Beautiful Bill (OB3) deductions requiring careful documentation.
Begin year-end tax planning conversations. October is the optimal window. Enough of the year has passed to project income accurately; enough time remains to implement strategies. Start with your highest-complexity clients.
Model SALT scenarios for high-income itemizers. Identify clients in high-tax states who itemize. The new 2026 $40,400 SALT cap combined with OB3’s phase-down for MAGI over $505,000 creates planning opportunities worth quantifying now.
Review Q3 payroll and excise filings. File Forms 941 and 720, Quarterly Federal Excise Tax Return, by October 30, and reconcile all year-to-date payroll data. October is also a good time to review payroll for any year-end bonus planning.

Key Compliance Dates

Thursday, October 1: Extended calendar-year Estates and Trusts (Form 1041) returns due.

Tuesday, October 13: Tips reporting for September (Form 4070). Extended due date for Form 941 Q3 if all deposits were made on time.

Wednesday, October 14: Special September deposit rule: Regular-method excise taxes deposit for the last 4 days of September.

Thursday, October 15: Extended Individual (1040) and Corporate (1120) returns due. Monthly payroll tax deposit for September (Form 941).

Tuesday, October 27: Communications and air transportation taxes deposit for the last 15 days of September.

Thursday, October 29: Regular-method excise taxes deposit for the first 15 days of October.

Intuit® Accountant Resources

Key Tax Facts for 2026 and Key Tax Facts for 2025
The October 2026 calendar with filing deadlines and reminders for you and your clients.
Tax update for TY26: Navigating the OB3 Act and more
One Big Beautiful Bill summary and tax changes
Navigating the tax landscape
IRS annual inflation adjustments for tax years 2025 and 2026

Nadia Rodriguez, CPA, CTC, is a Dallas-based tax advisor who has held her CPA license since 2009 and holds a master's degree in Taxation from the University of North Texas. She leads a boutique practice that helps individuals and closely held businesses with proactive planning, smart advisory, and accurate compliance. Nadia is the founder of Tax Training Academy, where she teaches bilingual, code-based courses built for working tax pros, and she also created the Nadia CPA Inner Circle, a welcoming community where tax professionals learn together and tackle real client challenges side by side. Earlier in her career, she contributed to Fortune 500 projects that helped modernize the tax profession and support fellow practitioners. Nadia has shared her work with state CPA societies, the NATP, the IRS Tax Forum, AICPA Engage, CPA Practice Advisor's Ensuring Success, Intuit Tax Pro Webinars, Latino Tax Fest, and Telemundo. Recognized as a "20 Under 40" Top Influencer, she serves her community in English and Spanish with clarity, care, and credibility. More from Nadia Rodriguez, CPA, CTC