Forcing Manual Calculation For a Workbook

Excel workbooks can become quite complex. In fact, it is possible to create workbooks that can take hours to calculate. The only problem with this, of course, is that when you open a workbook, it automatically recalculates if you have Excel configured to do that. This means that just opening a workbook can, in some instances, take hours.

One solution, of course, is to turn off automatic recalculation before you open the workbook. If you are like me, this solution isn't that great because my memory isn't always that great.

A better solution is to turn off automatic recalculation for certain workbooks. Since Excel doesn't allow you to specify manual or automatic recalculation on a workbook-by-workbook basis, you will need to add this feature through the use of a macro that automatically runs when the workbook is opened. This macro can turn off automatic recalculation, as shown here:

Private Sub Workbook_Open()
    Application.Calculation = xlManual
    Application.CalculateBeforeSave = False
End Sub

This macro must be placed in the ThisWorkbook project window. This means that you should open the workbook, press Alt+F11 to display the VBA Editor, and then double-click on the ThisWorkbook object in the Object Browser (upper-left corner of the VBA Editor window).

If you want, you can also place another macro right after the previous one. This macro is run automatically when the workbook is closed and, in this case, turns automatic recalculation back on:

Private Sub Workbook_BeforeClose(Cancel As Boolean)
    Application.Calculation = xlAutomatic
    Application.CalculateBeforeSave = True
End Sub

There is an important caveat to remember in relation to using this macro. You can only set the calculation mode for the application as a whole. Thus, with automatic recalculation turned off, no other worksheets will be automatically recalculated, either.