Why does this Excel file keep asking to save?

A client sent me some Excel .xlsx documents, and every time I open one of them and then close it, Excel asks if I would like to save changes, even if I didn't make any. This doesn't happen with any of my other Excel files. What is going on?

The files have no macros. I use Excel 2007.

Solution 1:

Copying from here:

This behavior occurs when something in the file has changed. Many times the user doesn't realize there are elements in the file that have been updated or calculated. Here are some examples of common scenarios:

• There is a volatile function used in the file. Examples of volatile formulas are listed in the more information section of this article.
• The file has been opened in a newer version and formulas have been calculated. See article in the more information section.
• A formula that contains a link to a formula in another workbook and that uses volatile functions.
• Linked pictures.
• Iterative formulas.
• Charts that are on chart sheets or that are embedded into worksheets but that have their source data in another workbook.
• VBA code that updates the workbook.

This list contains the cases mentioned in other answers as possibilities, and some others as well.

Solution 2:

One possibility is that the .xlsx file contains external links in at least one cell. Eg

Normally if you open this file you will be prompted with...

However, there is an annoying setting that throws people off in DATA/EDIT LINKS/START UP PROMPT/Dont display the alert and update links which overrides this prompt

Unfortunately, when you close the workbook you still get the prompt to save which will update the links.

This is one possible clue..?

EDIT:

Another possibility is the .xlsx contains a date formula such as NOW() or TODAY() which will prompt a save upon closing