September 2026 Tax Deadlines: What Businesses and Taxpayers Need to Know
September is a major tax deadline month, especially for business owners, partnerships, S corporations, and taxpayers making estimated tax payments.
The biggest date to circle on your calendar is September 15, 2026. Several important federal tax obligations fall on this date, making early preparation especially important.
September 15: A Major Deadline for Businesses
If your business received an extension earlier this year, September 15 is generally the filing deadline for:
S corporation returns using Form 1120-S
Partnership returns using Form 1065
These returns are particularly important because they generate Schedule K-1s, which business owners and partners may need to complete their personal tax returns.
For individuals who extended their personal returns until October 15, receiving an accurate K-1 on time can help prevent delays as the next filing deadline approaches.
Third Quarter Estimated Tax Payments Are Also Due
September 15 is also the deadline for the third installment of 2026 estimated federal income taxes for many:
Individuals
Self-employed taxpayers
Business owners
Calendar-year corporations
Trusts
If your income has changed significantly during the year, this may also be a good time to review whether your estimated payments still reflect your expected 2026 tax liability.
Paying too little throughout the year could potentially result in an unexpected balance or estimated tax penalties.
Other September 2026 Tax Dates to Remember
September 10
Employees who received tips during August may need to report them to their employer using Form 4070.
September 14
Certain regular-method excise tax deposits for the second half of August are due.
September 15
In addition to extended S corporation and partnership returns and estimated tax payments, the monthly payroll tax deposit for August may also be due for applicable employers.
September 25
Certain communications and air transportation tax deposits for the second half of August are due.
September 29
A special September deposit deadline applies to certain regular-method excise taxes covering the period from September 16 through September 26.
September 30
Certain August filings and payments are due, including:
Form 730, Monthly Tax Return for Wagers
Form 2290, Heavy Highway Vehicle Use Tax Return
Certain excise tax deposits subject to the special September rules
Business Owners: Consider a Retirement Plan Review
September can also be a useful time for business owners to revisit retirement and year-end tax planning.
Depending on your business, strategies involving cash balance plans or defined benefit plans may provide opportunities to increase retirement savings while potentially improving tax efficiency.
Some contributions may be made by the applicable tax return deadline, including extensions, but certain retirement plans must be established before the end of the year.
Starting the conversation now gives you more time to evaluate your options instead of making year-end decisions under pressure.
Don't Wait Until the Deadline
If your business has an extended return due September 15, now is the time to make sure your accountant has everything needed to complete the filing.
Missing information such as financial statements, bookkeeping records, payroll information, investment activity, or ownership changes can slow down preparation and potentially delay K-1s for owners and partners.
The same applies to estimated taxes. Changes in business income, investments, compensation, or other taxable income could mean the payment amount calculated earlier in the year no longer reflects your current situation.
Need Help Preparing for September Tax Deadlines?
Virtual CPAs can help you review upcoming filing requirements, estimated tax payments, business tax obligations, and year-end planning opportunities.
Being proactive now can make September deadlines easier to manage and help position you for a smoother October and year-end tax season.
This information is provided for general educational purposes and should not be considered individualized tax or financial advice. Tax rules and filing requirements may vary depending on your specific circumstances.