{"id":84224,"date":"2026-08-14T08:00:00","date_gmt":"2026-08-14T13:00:00","guid":{"rendered":"https:\/\/taxprocenter.proconnect.intuit.com\/?p=84224"},"modified":"2026-08-11T13:25:49","modified_gmt":"2026-08-11T18:25:49","slug":"key-tax-dates-and-to-do-list-september-2026","status":"publish","type":"post","link":"https:\/\/accountants.intuit.com\/taxprocenter\/tax-law-and-news\/key-tax-dates-and-to-do-list-september-2026\/","title":{"rendered":"Key tax dates and to-do list: September 2026"},"content":{"rendered":"\n

September is one of the busiest compliance months of the year, anchored by two deadlines that dominate the calendar: September 15 for extended returns for calendar-year S-corporations<\/a> (Form 1120-S<\/a>, U.S. Income Tax Return for an S Corporation<\/em>, and partnerships (Form 1065<\/a>, U.S. Return of Partnership Income<\/em>), along with Q3 2026 estimated tax payments for individuals, corporations, and trusts.<\/p>\n\n\n\n

For many firms, September 15 rivals April 15 in intensity, since it’s the final deadline for pass-through entities that extended in March, as well as any K-1s generated that day immediately become inputs for the individual returns still on extension until October 15. There are no major new extension deadlines beyond that single date, but the downstream effects ripple through the rest of the month as K-1 packages go out to individual clients and their preparers.<\/p>\n\n\n\n

The weeks leading up to the September 15 should be spent finalizing the entity returns that are actually ready, formally extending (via Form 7004<\/a>, if not already done) any entity that genuinely won’t make the deadline, and making sure staff aren’t burning hours chasing documents from clients who have gone quiet. Once the 15th passes, attention shifts immediately to distributing K-1s and flagging which individual returns now depend on them, since it’s only a short time until October 15. This is also a good month to review your firm’s fall staffing plan, since the individual extension deadline is only a month away and you’ll want capacity mapped out before it arrives.<\/p>\n\n\n\n

Along the way, be sure to pay attention to these important IRS and compliance deadlines.<\/p>\n\n\n\n

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2026 Tax Planning Guide<\/h2>\n\n\n\n

Unlock your firm’s potential for 2026 with the Intuit Accountants Tax Planning Guide. Gain essential strategies and insights to master evolving tax laws and deliver exceptional client value. Your roadmap to proactive tax planning starts here\u2014simply fill out the form to access your guide.<\/p>\n\n\n\n

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Get the Tax Guide<\/a><\/div>\n<\/div>\n<\/div><\/div>\n\n\n\n

In September<\/a>, it is recommended that you:<\/p>\n\n\n\n