Yes, since it is September and you likely did not have enough taxes paid during the year through paycheck withholding or estimated tax payments, you could still face a penalty for underpaying, even if you try to catch up now. The IRS calculates penalties by evaluating your tax payments quarter by quarter, so the shortfall from earlier quarters doesn’t disappear just because you increase your withholding in the final stretch. That having been said, there are ways to avoid or reduce penalties. Remember the IRS does have "safe harbor" rules that could help you as well:
- The 90% Rule: If your total payments for the year cover at least 90% of your current year's tax liability, you’re in the clear.
- The 100% Rule: If your payments cover 100% of the tax you owed last year, you're safe, too. (Though for higher earners—those with an adjusted gross income over $150,000 last year—the threshold rises to 110%.)
You can use the IRS's Withholding Estimator to make sure your current withholding and any remaining payments will at least meet one of these safe harbor thresholds. Even though you may still be hit with some penalty, increasing your withholding now will still help to decrease how much tax you will owe and the additional penalties.
Tax Deadlines
For most people filing taxes for fiscal year 2025, the final deadline to pay any taxes owed will be April 15, 2026.
But if you earn income that isn’t subject to withholding, like from freelancing, side hustles, investments, or self-employment, the IRS expects estimated quarterly payments throughout the year. For 2025, the deadlines were:
- Quarter 1: April 15, 2025
- Quarter 2: June 16, 2025
- Quarter 3: September 15, 2025
- Quarter 4: January 15, 2026
Since the September 15 deadline has already passed, it’s important to figure out what you owed for that quarter and make the payment as soon as possible to minimize any penalties.
For more information see:
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Please feel free to reach out with any additional questions and
thank you so much for attending!
Please have an amazing rest of your day!
Terri H.
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