Why is the IRS calculating Penalties Interest from 4/15/22 if filing deadline was 4/18/22?

[CharminRoll]

A relative of mine received a CP23 Notice from the IRS where penalties were assessed. Regardless of the content of the dispute, the Interest on the penalty is being calculated beginning April 15, 2022 when the filing deadline for TY2021 was April 18th. Also the IRS has PRE-DATED their letter as July 4, 2022; Today is June 28th.

Period

04/15/2022 -- 06/30/2022     76 Days      4.0%

06/30/2022 -- 07/04/2022     4 Days     5.0%

In this age of the Internet, she can electronically pay even before the first 75 days.

[NCperson]

@CharminRoll - I suspect because the 4th estimated payment was due on April 15. Was the amount due significant enough that estimated payments were required?

The interest will stop on the day the payment is received.  there will be no interest after that date. I suspect the letter is just providing the projection so you understand what could occur.  if she overpays, it will be  acredit on the account for 2022 tax year or returned 

[CharminRoll]

For TY2021 the 4th 1040ES payment was due on Jan 18, 2022.

For context, this dispute is for not filing an Extension and making payment. But the extension was filed and an estimated payment (over payment) was made by April 18, 2022. She has proof from the online service and the bank, so she's going to contest it.

But I thought it was strange how the IRS decided to assess interests that did not happen yet. They thought it'd take a whole week for the mail to get to her. The IRS must not trust USPS.

[NCperson]

@CharminRoll - I've re-read your post and you are correct, the 4th payment is January.

Just because the letter uses April 15th as the beginning of the late period, was any late charge ACTUALLY charged using that date?  What does the transcript reflect? Once the payment is made the interest should be adjusted to reflect the day of receipt of the payment (and I'd expect the interest clock would have begun on April 19th).