Thanks for the positive feedback, but I've already spotted an error, which should be fixed in this version:

Sub Button2_Click()

Worksheets("input").Unprotect Password:="nottherealpasswordwasjustquicker"
Worksheets("cashbook").Unprotect Password:="nottherealpasswordwasjustquicker"
 
Dim NewRow() As Variant
Dim TransNo As Integer
Dim lRowLoop As Long
Dim lSheet As Long
 
NewRow = Worksheets("input").Range("D12:BB12")
For lRowLoop = LBound(NewRow, 2) To UBound(NewRow, 2)
  NewRow(1, lRowLoop) = NewRow(1, lRowLoop) + 1
Next lRowLoop
TransNo = Worksheets("input").Range("D13").Value + 1
 
With Worksheets("cashbook")
  .Range(Cells(NewRow(1, LBound(NewRow, 2)), 2), Cells(NewRow(1, LBound(NewRow, 2)), 7)).Value = Worksheets("input").Range("B5:B10").Value
  .Cells(NewRow(LBound(NewRow)), 8).Value = .Cells(NewRow(1, LBound(NewRow, 2)) - 1, 8).Value + .Cells(NewRow(1, LBound(NewRow, 2)), 6).Value - .Cells(NewRow(1, LBound(NewRow, 2)), 7).Value
  .Cells(NewRow(1, LBound(NewRow, 2)), 1).Value = Worksheets("input").Range("D13").Value
End With

lSheet = Worksheets("input").Range("B6").Value

With Worksheets("P" & lSheet)
  .Unprotect Password:="nottherealpasswordwasjustquicker"
  .Range(Cells(NewRow(1, LBound(NewRow, 2) + lSheet), 2), Cells(NewRow(1, LBound(NewRow, 2) + lSheet), 7)).Value = Worksheets("input").Range("B5:B10").Value
  .Cells(NewRow(1, LBound(NewRow, 2) + lSheet), 8).Value = .Cells(NewRow(1, LBound(NewRow, 2) + lSheet) - 1, 8).Value + .Cells(NewRow(1, LBound(NewRow, 2) + lSheet), 6).Value - .Cells(NewRow(1, LBound(NewRow, 2) + lSheet), 7).Value
  .Cells(NewRow(1, LBound(NewRow, 2) + lSheet), 1).Value = Worksheets("input").Range("D13").Value
  Worksheets("input").Range("D12").Offset(0, lSheet).Value = NewRow(1, LBound(NewRow, 2) + lSheet)
  .Protect Password:="nottherealpasswordwasjustquicker"
End With

MsgBox "New Data added", vbOKOnly, "Test"
 
Worksheets("input").Range("B5:B10").ClearContents
Worksheets("input").Range("D12").Value = NewRow(1, LBound(NewRow, 2))
Worksheets("input").Range("D13").Value = TransNo
 
Worksheets("input").Range("B5").Select
 
Worksheets("input").Protect Password:="nottherealpasswordwasjustquicker"
Worksheets("cashbook").Protect Password:="nottherealpasswordwasjustquicker"

End Sub