Since you asked.I’m not completely sure of this, but it would seem that since the 4th quarter estimated tax payment date has passed, paying any amount owed now vs 4/15 would not impact the amount of penalty. And no interest on the penalty would start accruing until after 4/15. But I would like to be corrected if that’s wrong.
The penalty stops increasing when the required payment is made. If say a required 4th quarter payment is a day late (Jan 16) the penalty will be calculated as interest for a single day. Have a look at line 12 and 13 in Worksheet for Form 2210, Part III, Section B in the instructions for form 2210. If the text alone isn't convincing you might work an example or two. Try one where the payments are equal and sufficient but quarter 4 is a day late.
12 Number of days from the date on line 11 to the date the amount on line 1a was paid or 04/15/25, whichever is earlier
13 Underpayment on line 1a × Number of days on line 12 /365 × 0.07
Statistics: Posted by Epsilon Delta — Sat Feb 08, 2025 7:00 pm