Why Excel 365 keeps doing “cleanup” when you close it

The “cleanup” message when closing Excel 365 is typically caused by workbooks that contain a large number of unused but formatted cells, hidden content, or other internal structures that Excel has to process and optimize when saving/closing. This can make Excel appear to be stuck “cleaning up” and can persist every time the workbook is closed.

To reduce or stop this behavior, clean up the workbook so it uses less memory and has fewer unnecessary formatted cells:

1. Use Check Performance to remove unnecessary formatted cells
   • Open the affected workbook in Excel.
   • Go to Review > Check Performance.
   • In the Workbook Performance pane, review how many cells can be optimized.
   • Select Optimize all to clean up all sheets, or choose a sheet and select Optimize sheet to clean up only that sheet.
   • Save and close the workbook, then reopen and close it again to see if the cleanup message is reduced or gone.
   Note:
   • If any sheet is used for pixel art or relies on heavy cell formatting as “graphics,” do not use Optimize sheet or Optimize all on that sheet, as Excel will remove those formatted cells. If this happens accidentally, use Undo immediately.
2. Reduce memory-heavy workbook structures
   • Remove or simplify excessive formatting (especially entire-row/entire-column formatting) where possible.
   • Delete unused rows/columns that contain formatting or other hidden content.
   • Save the workbook after cleanup and test closing Excel again.

By reducing unnecessary formatted/hidden cells and optimizing the workbook, Excel has less to process on close, which typically stops the persistent “cleanup” behavior.

References:

• Cleanup cells in your workbook
• How to clean up an Excel workbook so that it uses less memory