Autofilling the last column

Hi,
I'm new to VBA, self taught from what I've read online and from recording marcos.

I have a spreadsheet that I need to insert a new column between the last column of data and the totals column.
The date row is on row 5 so just find the last column in that row and it gives me that last column.

That bit I can do.

I then need to autofill the formulas across from last column into the new column. I'm struggling to get this bit to work.
Below is what I have that works so far, I'm just now sure how to select the destination of the autofill.

Sub NewMonth()

Dim NewC As Long
Dim LastC As Long

'find last column

LastC = Cells(5, Columns.Count).End(xlToLeft).Column

'label the new column
NewC = Cells(5, Columns.Count).End(xlToLeft).Column + 1

'create new column
Columns(NewC).Select
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFillDefault

'copies the row across
Columns(LastC).Select
Selection.AutoFill Destination:=Columns(LastC & ":" & NewC), Type:=xlFillDefault

End Sub

Hi Dan,
Thanks for your reply, the reason I was opting for Autofill is I'm looking to change the cell reference. There's a monthly figures been shown on a summary page from umpteen worksheets so the cell references allow it to show figures from the relevant month.
I've now got the AutoFill to work for one row but I couldn't get it to work for multiple rows, so using your last row feature I've managed to achieve that.
Here's my code, it looks pretty busy it works haha.

Sub NewMonth()

If MsgBox("This add a new month to the sheet", vbYesNo) = vbNo Then Exit Sub

Dim NewC As Long
Dim LastC As Long
Dim LastR As Long

'find last column

LastC = Cells(5, Columns.Count).End(xlToLeft).Column
LastR = Cells(Rows.Count, LastC).End(xlUp).Row

'label the new column
NewC = Cells(5, Columns.Count).End(xlToLeft).Column + 1

'create new column
Columns(NewC).Select
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFillDefault

'copies the row across

Dim cellSource As Range
Dim cellTarget As Range

Set cellSource = Range(Cells(5, LastC), Cells(LastR, LastC))
Set cellTarget = Range(Cells(5, LastC), Cells(LastR, LastC + 1))

cellSource.AutoFill Destination:=cellTarget, Type:=xlFillDefault


End Sub

Thanks again for your help
Tom