Key Tax Deadlines for September 2025

As we head into September 2025, it's crucial to stay on top of pivotal tax-related deadlines that can have significant financial implications. This month is particularly important for employees working for tips and those making estimated tax payments. Let's dive into what you need to know to avoid penalties and set the stage for effective tax planning for 2026.

Strategies for 2025 Fall and 2026 Tax Preparation

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September 10 - Tip Reporting Deadline

For employees who have accumulated over $20 in tips during August, ensure that these are reported to your employer by September 10 using IRS Form 4070. Employers are obligated to withhold both FICA and federal income taxes based on these tips. In cases where regular wages don't suffice to cover these withholdings, your employer will annotate the uncollected amount on box 8 of your W-2. This requires you to account for the shortfall when filing your annual return.

September 15 - Estimated Tax Payment Requirement

It's time for your third estimated tax payment for 2025. Our tax system relies on a "pay-as-you-earn" model facilitated by several avenues, including:

  • Employee payroll withholding;
  • Retirees' pension withholding; and 
  • Self-employed individuals or those with additional income streams not subject to withholding through estimated tax payments.

If you fall short of a minimum "safe harbor" prepayment amount, be prepared for an underpayment penalty. This penalty accrues quarterly at the rate of the federal short-term rate plus three percentage points.

To bypass this penalty, you can exploit two main safe harbors. The first requires that your payments equate to 90% or more of the current year's tax. The second relies on last year's liabilities, generally requiring prepayments to be at least 100% of the prior year’s taxes—or 110% if your Adjusted Gross Income (AGI) exceeds $150,000 (or $75,000 for separate filers).

Illustrative Example: Assume your total tax for 2025 is $10,000 but you've only prepaid $5,600. You'd need $9,000 to meet the first safe harbor, indicating you'd incur a penalty. However, if last year's tax was $5,000 and you've prepaid $5,600, you qualify under the second safe harbor since $5,600 surpasses 110% of your previous year’s tax.

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This scenario underscores the essence of ensuring adequate prepayments—an aspect not to be overlooked especially when experiencing income increases, such as asset sales or bonuses. Remember, timely installment payments are vital for meeting the safe harbor criteria. If you're unsure about your prepayment position, do contact our office for expert advice.

BEWARE: Individual state rules regarding de minimis amounts and safe harbor can deviate from federal standards. Get in touch with us for state-specific estimates advice.

Weekend and Holiday Extensions: Tax deadline extensions apply if the due date coincides with a Saturday, Sunday, or federal holiday, shifting to the next business day.

Disaster Area Extensions:
Special provisions apply to designated disaster zones, granting filing extensions. Confirm these via FEMA’s site or consult the IRS page for updated relief information.

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