If a person owes more than $1k, there is a penalty for under-withholding (exceptions apply, yada yada).

Basically, the penalty is interest, at 5% per year, figured daily calculated from 12/31 to 4/15. If you pay early, you get to subtract, based on number of days before 4/15, yada yada. 

The IRS will figure this penalty for you. Software should be able to figure it correctly. So could anyone who can do math.

The 2019 Form 2210 still shows the date 4/15, even though the due date is now 7/15.

So here's the question. Is the penalty still based on daily interest? In other words, let's say my client owes $1200, and doesn't plan to pay before 7/15. The penalty is figured as $13, but that would be if they paid by 4/15. Is the IRS waiving the next 3 months of penalty? Or has the software just not updated itself (and the forms also haven't updated themselves....)?

Curious minds want to know.

I know it's only another $10, but for some clients, that is a big difference. (They shouldn't have under-withheld, but that's another story.)