Add a week to a range of dates in VBA - excel

Question

In sheet INPUT, rows of data for week schedule gets inputted. Multiple rows per day is possible. Column A contains the dates of the original week of the schedule. When the complete planning is set in the INPUT sheet (lets say 15 rows by 10 columns of data) a macro can be run which copies the planning to the OUTPUT sheet and creates it for a full year. Therefore I'm coding VBA to copy the block of data and paste it beneath the previous week and update the dates by 7 days.
I'm having difficulties with DateAdd function.
Does anyone know a good solution?
Dim i As Integer
Dim rowCount As Long
Dim columnCount As Long
Sheets("OUTPUT").Select
Sheets("OUTPUT").Cells.Clear
Sheets("INPUT").Select
rowCount = Sheets("INPUT").Range("A6", Sheets("INPUT").Range("A6").End(xlDown)).Rows.Count - 1
columnCount = Sheets("INPUT").Range("A5", Sheets("INPUT").Range("A5").End(xlToRight)).Columns.Count - 1
Range("A5").Select
Range(Selection, Selection.End(xlToRight)).Select
Range(Selection, Selection.End(xlDown)).Select
Selection.Copy
Sheets("OUTPUT").Select
Range("A1").Select
ActiveSheet.Paste
For i = 1 To 51
Range("A" & Rows.Count).End(xlUp).Select
Range(Selection, Selection.Offset(-rowCount, columnCount)).Copy
Range("A" & Rows.Count).End(xlUp).Select
ActiveCell.Offset(1, 0).PasteSpecial
Range("A" & Rows.Count).End(xlUp).Select
Range(Selection, Selection.Offset(-rowCount, 0)).Value = DateAdd("d", 7, Range(Selection, Selection.Offset(-rowCount, 0)).Value)
Next i

Answer 1

Variable= DateAdd("d", 7, Variable)

Answer 2

I'm not entirely sure what you do with columnCount so this may need to be modified, but I think something like this should get you started
Dim dateVals
Dim destRange as Range
Dim cl as Range
For i = 1 To 51
' initial data
' this gets a range from the last cell in column A, offset by the rowCount variable, and resized based on row/col counters
Set rng = Range("A" & Rows.Count).End(xlUp).Offset(-rowCount).Resize(rowCount,colu‌​mnCount)
' similar size range beginning in row after 'rng'
Set destRange = rng.Offset(rng.Rows.Count)
' Instead of copying the cells/paste special, just transfer the values directly
' Range(rng, rng.Offset(-rowCount, columnCount)).Copy
destRange.Value = rng.Value
' Add 7 days to each cell value
' I assume you only have date values in column 1
For Each cl in destRange.Columns(1).Cells
cl.Value = DateAdd("d", 7, CDate(cl.Value))
Next
Next i