Optimize code to minimize runtime of the macro

Question

I have been writing some macros to perform some astrological calculations (calculating sign, lunar mansion, D9 & D60). The raw data is in the following format:

Answer 1

There are a couple of things you can do. First of all, declaring all variable saves memory which in turn saves time. That being said, the real time consuming factor in your code is the looping through each cell. The fastest way to obtain the same result is to read the data into an array and then write the array to the output sheet. In the following code, I have edited your prepareOutput sub in such a way, that it keeps your initial code structure, but instead of looping through and writing to each cell, it now reads the data into an array and then writes this array to the desired output area.

Sub prepareOutput()
    Application.ScreenUpdating = False
    Dim c As Range, d As Range, l As Range, ll As Range, r As Range
    Dim count As Integer
    Dim ArrDim As Integer, CurrVal As Integer
    Dim OutRng As Range
    Dim TempArr() As String

    'Defines worksheets
    Dim WsEmph As Worksheet, WsOut As Worksheet
    Set WsEmph = ActiveWorkbook.Sheets("Ephemerides")
    Set WsOut = ActiveWorkbook.Sheets("Output")

    Set r = WsEmph.Range("a4:" & Worksheets("Ephemerides").Range("a4").End(xlDown).Address)

    WsOut.Range("a3").Value = "Date"
    For Each d In r
        WsOut.Cells(d.Row, 1).Value = d.Value
    Next

    For Each c In WsEmph.Range("d2:o2")
        If Not IsEmpty(c) Then
            count = count + 5

            'Redimension of temporary array
            ArrDim = WsEmph.Range(c.Offset(2, 0), c.End(xlDown)).Rows.count
            ReDim TempArr(1 To ArrDim, 1 To 2)
            CurrVal = 1

            If count = 5 Then
                With WsOut
                    .Cells(2, 2).Value = c.Value
                    .Cells(3, 2).Value = "Longitude"
                    .Cells(3, 3).Value = "Sign"
                    .Cells(3, 4).Value = "Nakshatra"
                    .Cells(3, 5).Value = "Navamsa"
                    .Cells(3, 6).Value = "D60"
                End With

                For Each l In WsEmph.Range(c.Offset(2, 0), c.End(xlDown).Address)
                    'Fills array
                    TempArr(CurrVal, 1) = l.Value
                    TempArr(CurrVal, 2) = calcSign(l.Value)
                    CurrVal = CurrVal + 1
                Next
                    'Sets output range and writes data
                    Set OutRng = WsOut.Range(WsOut.Cells(c.Offset(2, 0).Row, 2), WsOut.Cells(c.End(xlDown).Row, 3))
                    OutRng = TempArr
                    count = 2
            Else
                With WsOut
                    .Cells(2, count).Value = c.Value
                    .Cells(3, count).Value = "Longitude"
                    .Cells(3, count + 1).Value = "Sign"
                    .Cells(3, count + 2).Value = "Nakshatra"
                    .Cells(3, count + 3).Value = "Navamsa"
                    .Cells(3, count + 4).Value = "D60"
                End With

                For Each ll In WsEmph.Range(c.Offset(2, 0), c.End(xlDown).Address)
                    'Fills array
                    TempArr(CurrVal, 1) = ll.Value
                    TempArr(CurrVal, 2) = calcSign(ll.Value)
                    CurrVal = CurrVal + 1
                Next
                    'Sets output range and writes data
                    Set OutRng = WsOut.Range(WsOut.Cells(c.Offset(2, 0).Row, count), WsOut.Cells(c.End(xlDown).Row, count + 1))
                    OutRng = TempArr
            End If
        End If
    Next
    Application.ScreenUpdating = True
End Sub

On my system, running your code took 25.16 seconds. With the above changes to the code it now takes just 3.16 seconds to perform the same task.

Note that I have also declared all variables and used worksheet-variables as refference to each worksheet. All though the latter doesn't improve speed, it only improves the readability of the code.