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

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.