Macro Runs Slowly, but Steps Quickly

Fredric wrote about a problem he was having with a macro. When he is running the macro in the VB Editor using F8 (stepping through the macro), it completes in just a few minutes. When he runs the macro outright, it seems to take forever to run, often taking 20 minutes or more to execute. Even though Fredric's workbook is large (46 MB), the time differential between the two methods of running is bothersome.

Problems like this can be baffling, and they often take some heavy-duty analysis in order to figure out. A good place to start is to add some "timer code" in your macro. Add a small routine that saves a time value and another routine that compares that saved value to the current time and displays the difference. At the beginning of a section of code you want to analyze, you call the first routine (which saves the start time) and then at the end of the section of code you call the second routine. In that way, you can determine which portions of your code are taking the longest time to execute. These are the code sections you then focus on, so you can figure out what they are doing that is taking so long.

Another thing to make sure is that you add these two lines at the beginning of your macro:

Application.ScreenUpdating = False
Application.EnableEvents = False

These turn off screen updating, which can slow down a running macro, and disable events. This last line is included so that changes done by the macro in your worksheet won't trigger Excel's recalculation routines. If your macro is making a lot of changes in the data in the worksheet, and a full recalculation is triggered after each change, then with such a large workbook, lots and lots of time can be spent just doing the recalc. At the end of your macro, you reverse the effect of the two lines you added:

Application.EnableEvents = True
Application.ScreenUpdating = True

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (2436) 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: Macro Runs Slowly, but Steps Quickly.