Key Tax Deadlines for September 2025: Staying Compliant and Prepared

As we approach September 2025, it's crucial to keep abreast of important tax deadlines. This month, specific due dates like tip reporting and estimated tax payments call for your attention. We'll explore safe harbor rules, strategies to avoid penalties, and essential planning to ensure a smooth transition into 2026.

Securing Your Financial Future for 2025 and 2026

Proactively engaging in tax planning can provide substantial benefits. Reach out to our office to schedule a personalized consultation, ensuring that your financial strategies align with your objectives.

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September 10: Declare Tips to Your Employer

Employees who receive over $20 in tips during August must report these tips to their employer using IRS Form 4070 by September 10. Employers are obligated to withhold FICA taxes and income tax. If your regular wages aren't sufficient to cover these withholdings, any uncollected amount will be indicated in box 8 of your W-2. It will then be your responsibility to settle this with your annual tax return.

September 15: Estimated Tax Payment Deadline

For those making estimated tax payments, the third installment for 2025 is due by September 15. The "pay-as-you-earn" system allows several methods to help meet this requirement, including:

  • Withholding from employee payroll;

  • Pension withholding for retirees; and

  • Estimated tax payments for the self-employed or those with untaxed income sources.

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Avoiding the underpayment penalty involves meeting safe harbor requirements. This penalty comprises the federal short-term rate plus 3%, assessed quarterly. You can avoid it if your underpayment is below the $1,000 de minimis threshold, or by adhering to "safe harbor" payment methods:

  • Current-year payments meet or exceed 90% of your tax liability;

  • Prior-year payments cover 100% of your last year's tax (110% if your AGI exceeds $150,000 or $75,000 for married filing separately).

Consideration Example: If your annual tax is $10,000 and prepayments are $5,600, you owe an additional $4,400. For the first safe harbor, prepayments are insufficient as 90% of $10,000 is $9,000. However, if last year's tax was $5,000 and you prepaid $5,600, exceeding 110% of the previous year's tax ($5,500), you qualify for this safe harbor, thus avoiding a penalty.

Such examples highlight the importance of adequate prepayments, especially with significant income changes from stock sales, property transactions, or bonuses. Ensure you meet each required estimated tax installment to qualify for penalty exceptions. For safe harbor estimates or related inquiries, contact our office without delay.

Note: State-specific de minimis amounts and safe harbor rules may differ from federal guidelines. Consult our team for state-specific advice.

Weekend & Holiday Adjustments:

If a due date coincides with a weekend or legal holiday, it moves to the next non-holiday business day.

Disaster Area Extensions:
If a geographic area becomes a designated disaster zone, deadlines extend accordingly. For updates on disaster zones and extended dates, visit:

FEMA's Disaster Declarations: FEMA Site
IRS Tax Relief: IRS Site

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