Using the DateDiff function in VBA to get number of days between 2 dates - datediff

Question

so I'm trying to get 2 dates in an excel sheet and use the DateDiff function to get the number of days between the 2 dates. I am essentially adding the number of days together and dividing by the the number of rows to get and average amount of days. So far I have it to where the total amount of days for every row gets added together and is displayed on column "E" and the number of rows is placed on column "F". I know I am close because at one point it worked but I was dumb and changed something and now i does not. here is my code and the excel sheet.
Sub GetDays()
Range("C1").Select
Do Until ActiveCell.Value = ""
date1 = DateValue(ActiveCell.Offset(1, 0).Value)
date2 = DateValue(ActiveCell.Offset(1, 0).EntireRow.Cells(1, "D").Value)
DayCount = DateDiff("d", date1, date2) + DayCount
ActiveCell.Offset(1, 0).EntireRow.Cells(1, "E").Value = DayCount
StudentCount = StudentCount + 1
ActiveCell.Offset(1, 0).EntireRow.Cells(1, "F").Value = StudentCount
ActiveCell.Offset(1, 0).Select
Loop
End Sub!
Here is a snippet of the sheet

Answer 1

The issue I discovered when testing your code is that your loop is comparing to the ActiveCell value to determine when to exit, but then your code is operating on the cell below ActiveCell, as a result of the Offset(1,0) call. So when your loop is on the last line of data, ActiveCell.Value = "3/25/2015 10:52", but your next line of code is trying to populate date1 with the DateValue of a null since it is offset down one row. This throws a Type Mismatch error.
I've adjusted your code below, this works for me:
Sub GetDays()
Range("C1").Select
Do Until ActiveCell.Value = ""
date1 = DateValue(ActiveCell.Value)
date2 = DateValue(ActiveCell.Offset(0, 1).Value)
DayCount = DateDiff("d", date1, date2) + DayCount
ActiveCell.Offset(0, 2).Value = DayCount
StudentCount = StudentCount + 1
ActiveCell.Offset(0, 3).Value = StudentCount
ActiveCell.Offset(1, 0).Select
Loop
End Sub
I adjusted the offset command so that we are looking at the same row at all times each loop. I replaced the "EntireRow.Cells(1, "D")" sections by just using the column integer in Offset().
You may need to change the second line to: Range ("C2").Select for my code to work, depending on if your data starts on row 1 or row 2.