A tax expert is advising taxpayers to mark Jan 15. on the calendar to avoid expensive penalties and interest.

Roy Abramowitz says if one doesn't pay their final 2025 estimated taxes by that date, they could end up owing the IRS expensive penalties and interest.

"If you go on extension on April 15, you must pay your taxes due by that date. Remember, it's an extension of time to file, not an extension of time to pay. So if you do not pay the taxes due on April 15, your tax return extension will be invalid," Abramowitz says.

He adds taxpayers could also end up owing interest, underpayment, and late filing penalties.