Just calculate the first of the next month and subtract a day:
Date(If(Month([Done Date]) = 12,Year([Done Date]) + 1,Year([Done Date])),If(Month([Done Date]) = 12,1,Month([Done Date]) + 1),1) - Days(1)
Just calculate the first of the next month and subtract a day:
Date(If(Month([Done Date]) = 12,Year([Done Date]) + 1,Year([Done Date])),If(Month([Done Date]) = 12,1,Month([Done Date]) + 1),1) - Days(1)