Excel filtering very slow
This usually happens because Excel thinks the data set is much larger than it actually is. For instance, if someone had navigated to cell A1048576 and formatted it, even though it might not look different, now Excel thinks you have over a million rows. Test this by selecting cell A1 and then hitting CTRL + End. This will take you to what Excel believes is the last cell in the worksheet. If this is the issue you can delete all the rows and/or columns after where your actual data ends, save the file, close it, and reopen it. This should stop Excel from seeing all those empty cells as part of the data. If this doesn't work, selecting your data and pasting it into a new file should fix it.
- Select All (Ctrl+A)
- Go to Home -> Editing -> Clear -> Clear Formats.
- Save file and re-apply filter.
You're done. It works for me every time; please let me know if it works for you!