IRS Tax Deadlines & Extensions: What You Need to Know Before Year-End

The fourth quarter of 2026 is here, and that means one thing for taxpayers: the clock is ticking. Whether you filed an extension back in April or you're a small business owner managing quarterly payments, there are critical IRS deadlines between now and December 31 that you cannot afford to miss.

If you are self-employed, a freelancer, a gig worker, or a small business owner, you are required to pay estimated taxes four times per year. The fourth and final installment for the 2026 tax year is due January 15, 2027.

Missing this payment can result in an underpayment penalty — even if you plan to pay in full when you file in April. The safe harbor rule says you generally avoid penalties if you pay at least 90% of your current year tax liability or 100% of last year's tax (110% if your income exceeds $150,000).

What to do now: Review your income for the year, calculate your estimated liability, and make your Q4 payment through IRS Direct Pay or EFTPS before the deadline.

If you filed a six-month extension in April, your final return was due October 15, 2026. If you missed that date, your return is now late and penalties are accruing daily.

The failure-to-file penalty is 5% of unpaid taxes per month, up to 25%. The failure-to-pay penalty is 0.5% per month. Together, these can add up quickly. File as soon as possible to stop the clock.

Important: An extension to file is never an extension to pay. Any taxes owed were still due on April 15. If you owe and have not paid, interest has been accumulating since that date.

The final months of the year are your last opportunity to reduce your 2026 tax bill before December 31:

• Maximize retirement contributions. Contributions to a traditional IRA or 401(k) reduce your taxable income. The 2026 401(k) contribution limit is $23,500 ($31,000 if you are 50 or older).
• Harvest investment losses. If you have investments that have declined in value, selling them before year-end can offset capital gains elsewhere in your portfolio.
• Accelerate deductible expenses. If you itemize, consider paying deductible expenses — charitable donations, medical bills, property taxes — before December 31.
• Review your withholding. Use the IRS Tax Withholding Estimator to make sure you are not heading into April with a large balance due.

If you operate through an S-corporation or partnership, your 2026 return (Form 1120-S or 1065) was due March 15, 2026, with an extension to September 15, 2026. If you missed the extended deadline, file immediately and consider requesting penalty abatement if you have a history of compliance.

At AMGUS, our bilingual tax team serves individuals, families, and small businesses throughout Florida and the El Paso region. Whether you need help with a late return, estimated payments, or year-end planning, we are ready to assist — in English or Spanish.

Do not wait until April. The decisions you make in the next 60 days can significantly impact what you owe.

Contact AMGUS today to schedule a year-end tax review.

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