Date Calculations

I am new to acrobat and am trying to create a few short scripts that ultimately calculates interest. Here is what I am looking to do:

1. No matter what Date of Payment is entered is, the next box (labeled “Interest From”) will show the first day of the following month.  Example:  If 04/15/17 is entered as the Payment Date, the “Interest From” box would show May 1, 2017. So, I’d need a script to do that part.
2. No matter what date the tenant moved out, the date in the next box (labeled “Interest To”) would show the last day of that same month.  Example:  Move Out Date is 09/10/17, then the “Interest To” box would show 09/30/17.  This would be another script.
3. Calculate the number of months from “Interest From” to “Interest To”.  This would be a separate script also (In this example it would be 5 months).

Items 1-3 would be in separate boxes (fields?Cells?) so they would be 3 separate scripts.  I want it this way so the tenant can clearly see the Date of Payment, Interest From Date, Interest To Date, Number of Months used in the interest calculation, and Interest Earned.

So basically, all I am trying to accomplish is an interest calculation from the first day of the month following Date of Payment to the last day of the month the tenant moves out. I just can’t seem to figure out the date calculation.  I have an Excel sheet with macros to do this, but can’t seem to figure it out in Acrobat. Thanks!