How to make the Potential Closing date be the end of the month automatically?
You need to create a new custom field - formula field to “complement” Closing Date (the standard Closing Date is required and can’t be hidden) and use the following formula: Newdate(Year(${Potentials.Closing Date}),Month(${Potentials.Closing Date}),If(Or(Month(${Potentials.Closing Date})==1,Month(${Potentials.Closing Date})==3,Month(${Potentials.Closing Date})==5,Month(${Potentials.Closing Date})==7,Month(${Potentials.Closing Date})==8,Month(${Potentials.Closing Date})==10,Month(${Potentials.Closing Date})==12),31,If(Or(Month(${Potentials.Closing Date})==4,Month(${Potentials.Closing Date})==6,Month(${Potentials.Closing Date})==9,Month(${Potentials.Closing Date})==11),30,28)),11,59,'PM') As you can see it is relatively crude but this is the only way to do it.
Note also that I ignore the 29 Feb in leap year scenario. Easy to add but makes the formula a lot more complex so for one day every 4 years I didn’t think it worth the effort.