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September 2026 Tax Due Dates: Keep Your Financial Foundation Solid

As fall approaches, it is an ideal time to review your 2026 tax situation and begin planning for 2027. We believe in the “three-legged stool” of business stability: keeping your books accurate, your taxes optimized, and your payroll on time. With an important estimated tax deadline approaching this month, now is a great opportunity to ensure that middle leg is solid. Reviewing your income, withholding, and estimated payments now can highlight whether any adjustments should be made before year-end.

September 10: Report August Tips to Your Employer

If you are an employee who works for tips and you received more than $20 in tips during August, you are required to report them to your employer no later than September 10. You can use IRS Form 4070 or provide your own signed statement. This statement must include your name, address, and Social Security number; your employer’s name (or the establishment’s name) and address; the specific month or period the report covers; and the total amount of tips received during that timeframe.

Your employer is required to withhold FICA taxes and income tax withholding for these tips from your regular wages. If your regular wages are insufficient to cover these taxes, the employer will report the amount of the uncollected withholding in box 8 of your W-2 for the year. You will then be required to pay the uncollected withholding when you file your annual return.

September 15: Third Quarter Estimated Tax Deadline

The third installment of 2026 individual estimated taxes is due on September 15. The federal tax system is built on a “pay-as-you-earn” concept. To facilitate this, the government provides several means to assist taxpayers in meeting the requirement:

  • Payroll withholding for employees;

  • Pension withholding for retirees; and

  • Estimated tax payments for self-employed individuals and those with other sources of income not covered by withholding.

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Understanding the Underpayment Penalty and Safe Harbors

When a taxpayer fails to prepay a safe harbor (minimum) amount, they can be subject to the underpayment penalty. This penalty is equal to the federal short-term rate plus 3 percentage points, and it is computed on a quarter-by-quarter basis.

Federal tax law provides specific ways to avoid this penalty. First, if the underpayment is less than $1,000 (the de minimis amount), no penalty is assessed. In addition, the law provides two primary "safe harbor" prepayments:

  • The first safe harbor is based on the tax owed in the current year. If your payments equal or exceed 90% of what is owed in the current year, you escape the penalty.

  • The second safe harbor is based on the tax owed in the immediately preceding tax year. This is generally 100% of the prior year’s tax liability. However, for taxpayers whose Adjusted Gross Income (AGI) exceeds $150,000 ($75,000 for married taxpayers filing separately), the safe harbor becomes 110% of the prior year’s tax.

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How Safe Harbors Work in Practice

Suppose your tax for the year is $10,000 and your prepayments total $5,600. As a result, you owe an additional $4,400 on your tax return. To find out if you owe a penalty, we first see if you meet the 90% safe harbor. Since 90% of $10,000 is $9,000, your prepayments fell short. You cannot avoid the penalty under this exception.

However, the second safe harbor may still apply. Assume your prior year’s tax was $5,000. Because you prepaid $5,600, which is greater than 110% of the prior year’s tax ($5,500), you qualify for this safe harbor and escape the penalty.

This underscores the importance of making sure your prepayments are adequate, especially if you experience a large increase in income from the sale of stocks or property, large bonuses, or retirement. Timely payment of each required estimated tax installment is strictly required to meet the safe harbor exception.

CAUTION: Some state de minimis amounts, safe harbor estimate rules, and estimated payment due dates differ from federal guidelines. Please contact our office for the specific state rules that apply to you.

Weekend and Holiday Adjustments

If a tax due date falls on a Saturday, Sunday, or legal holiday, the deadline is automatically extended until the next business day that is not itself a legal holiday.

Extensions for Designated Disaster Areas

When a geographical area is designated as a disaster area, tax due dates will be extended. For more information on whether your area has been designated a disaster area and the exact filing extension dates, visit the following websites:

FEMA: https://www.fema.gov/disaster/declarations
IRS: https://www.irs.gov/newsroom/tax-relief-in-disaster-situations

Keep Your Taxes Optimized Through Year-End

Staying current with estimated payments and tip reporting ensures your business has the stability it needs to grow. Rooted in Montana values of simplicity and lasting relationships, we are here to provide practical solutions tailored to subcontractors, real estate professionals, and service business owners across the region.

If you have questions regarding your safe harbor estimates or want to proactively plan for the months ahead, contact our Billings office today to schedule a tax planning consultation.

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