Compare Excel Spreadsheets

Usually what I would do is copy the Excel spreadsheets into Word, then use Word's Merge Documents feature (might have been Merge/Compare or simply Compare Documents previously to 2011) to see the differences between them. Depending on how big your spreadsheet is, however, that might not work for you.

There is a Mac version of Araxis Merge, which is an excellent program for comparing and merging mange kinds of files, and folders of files.

Its History page seems to suggest that it does compare Excel files on Mac.

There's a 30 day evaluation, so you could try it out and see if it does what you need.

(I have no affiliation with the company - am just a very frequent user of the Windows version of the tool)

You might want to try this tool. It does the job and it's free. http://www.nunobrum.com/excelcomparator.html

It works in Windows and on MAC OSX. It's based on a VBA macro running in the native Excel Application, so it doesn't need any installations. Only suffice to enable the Macros and it works. Contrary to other Excel comparators, this one also enables you to compare different sheets of the same workbook or, different ranges of the same sheet. Compares Values or Formulas. This tool annotates the differences directly on the sheets you are comparing, and offers the possibility of navigating through the differences on the Report sheet.

Note: the author of this answer is also the author of this donationware software.