Determining if Calculation is Necessary

Excel allows you to control when it recalculates a worksheet. Normally, Excel recalculates anytime you change something in a cell. If you are working with very large worksheets that have lots of formulas in them, you may want to turn off the automatic recalculation feature. You can turn off automatic recalculation using controls on the Calculation tab of the Options dialog box.

Your macros can also force Excel to recalculate your worksheet. If you have automatic recalculation turned on, then any change your macro makes in a worksheet will force Excel to recalculate. If you have automatic recalculation turned off, then you can use the Calculate method to recalculate a worksheet:

ActiveSheet.Calculate

Of course, if recalculation takes quite a while to perform, you might want to check to see if a recalculation is necessary before actually forcing one. It appears that there is no flag you can directly check to see if a recalculation is necessary. The closest thing is to check the Workbook object's Saved property. This property essentially acts as a "dirty flag" for the entire workbook. If there are unsaved changes in a workbook, then the Saved property is False; if everything is saved, then it is True.

How does this help you figure out if a recalculation is necessary? Remember that calculation is only necessary when there are changes in a worksheet. Changing anything in a worksheet will also set the workbook's Saved property to False. Thus, you could check the Saved property before doing the recalculation, as shown here:

If Not ActiveWorkbook.Saved Then
    ActiveSheet.Calculate
End If

There is only one problem with this approach, of course—the Saved property is only set to True if the workbook is actually saved. This means that you could recalculate multiple times without really needing to do so, unless you tie saving and recalculation together, as shown here:

If Not ActiveWorkbook.Saved Then
    ActiveSheet.Calculate
    ActiveWorkbook.Save
End If

The wisdom of approaching this problem in this manner depends on the nature of your particular situation. If it takes longer to save the workbook than it does to simply recalculate, then this approach won't work. If, however, recalculation takes longer (which is very possible with some types of operations), then this approach may work well.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (2323) applies to Microsoft Excel 97, 2000, 2002, and 2003. You can find a version of this tip for the ribbon interface of Excel (Excel 2007 and later) here: Determining if Calculation is Necessary.