Macro to Auto Fill Down to last adjacent cells - vba

Question

I want my macro to populate my formulas all the way down the sheet. Every time I run the macro it stops at row 13662 because that was the last row when I was recording it, but the last row changes constantly. Is there a way to do this?
The columns I need to do this for are N, I, J, K, and L. Any help appreciated. See code below.
Sub Weekly_Expiring_Rebate_Report()
'
' Weekly_Expiring_Rebate_Report Macro
'
'
Columns("A:A").Select
Range(Selection, Selection.End(xlToRight)).Select
With Selection
.VerticalAlignment = xlBottom
.WrapText = True
.Orientation = 0
.AddIndent = False
.IndentLevel = 0
.ShrinkToFit = False
.ReadingOrder = xlContext
.MergeCells = False
End With
With Selection
.VerticalAlignment = xlBottom
.WrapText = False
.Orientation = 0
.AddIndent = False
.IndentLevel = 0
.ShrinkToFit = False
.ReadingOrder = xlContext
.MergeCells = False
End With
Columns("A:A").Select
Range(Selection, Selection.End(xlToRight)).Select
Columns("A:Z").EntireColumn.AutoFit
Columns("N:N").Select
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
Selection.NumberFormat = "General"
Range("N1").Select
ActiveCell.FormulaR1C1 = "Expiring Rebate Status"
Range("N2").Select
Columns("N:N").EntireColumn.AutoFit
ActiveCell.FormulaR1C1 = "=VLOOKUP(RC[-1],'Status IND'!C[-13]:C[-11],3,FALSE)"
Range("N2").Select
Selection.AutoFill Destination:=Range("N2:N13662")
Range("N2:N13662").Select
Columns("I:I").Select
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
Range("I2").Select
ActiveCell.FormulaR1C1 = "=LEFT(RC[-1],4)"
Range("I2").Select
Selection.AutoFill Destination:=Range("I2:I13662")
Range("I2:I13662").Select
Range("J2").Select
ActiveCell.FormulaR1C1 = "=LEFT(RC[-2],6)"
Range("J2").Select
Selection.AutoFill Destination:=Range("J2:J13662")
Range("J2:J13662").Select
Range("K2").Select
ActiveCell.FormulaR1C1 = "=RIGHT(RC[-1],2)"
Range("K2").Select
Selection.AutoFill Destination:=Range("K2:K13662")
Range("K2:K13662").Select
Range("L2").Select
ActiveCell.FormulaR1C1 = "=RIGHT(RC[-4],2)"
Range("L2").Select
Selection.AutoFill Destination:=Range("L2:L13662")
Range("L2:L13662").Select
Range("I1").Select
ActiveCell.FormulaR1C1 = "EXP_YEAR"
Range("K1").Select
ActiveCell.FormulaR1C1 = "EXP_MONTH"
Range("L1").Select
ActiveCell.FormulaR1C1 = "EXP_DAY"
Columns("I:L").Select
Range("L1").Activate
Selection.Copy
Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
:=False, Transpose:=False
Columns("J:J").Select
Application.CutCopyMode = False
Selection.Delete Shift:=xlToLeft
Range("L1").Select
ActiveCell.FormulaR1C1 = "EXP_Month_Name"
Columns("I:L").Select
Range("L1").Activate
Columns("I:L").EntireColumn.AutoFit
Range("L2").Select
ActiveCell.FormulaR1C1 = "=VLOOKUP(RC[-2],Month!C[-11]:C[-10],2,FALSE)"
Range("L2").Select
Selection.AutoFill Destination:=Range("L2:L13662")
Range("L2:L13662").Select
ActiveWindow.SmallScroll Down:=-6
Columns("M:M").Select
End Sub

Answer 1

It looks like your issue is on the 5th row from the end.
Based on this answer you could replace:
Selection.AutoFill Destination:=Range("L2:L13662")
with
Selection.AutoFill Destination:=Range("L2:L" & ActiveSheet.UsedRange.Rows.Count)

Answer 2

Here is an example of vba code that I think will work for your purposes.
'Counts the number of rows in column "C" and then places
'concatenation formula in each adjacent cell (in column "D").
Range("D2:D" & Range("C" & Rows.Count).End(xlUp).Row).Formula = "=CONCATENATE(C2,"", "",B2)"