Excel for Mac 2011 uses the same default file format as Excel 2010 and 2013 on Windows -- XLSX -- so you don't need to convert your file to a different type when sending it from a Mac to a Windows PC. The two systems do have a few differences, however, so look over your workbook to check for features that can cause compatibility issues.
Save as XLSX
Excel on Mac saves in the XLSX format by default, but Excel for Mac sometimes hides the file extension, which Windows uses when opening a file. In the Save As dialog box, choose Excel Workbook (.xlsx) as the format and uncheck Hide Extension. Do not include slashes, backslashes, colons, greater-than signs, less-than signs, question marks, quotation marks, asterisks or vertical bars in the file name.
If you're sending a file to an Excel version before 2007, choose Excel 97-2004 Workbook (.xls) as the format instead.
Check the Compatibility Report
Excel for Mac can scan for compatibility issues with other versions of Excel. Open the View menu and click Compatibility Report. Choose a version of Excel in the Check Compatibility With drop-down menu and click Check Document. If a compatibility problem turns up, select it and click Fix to attempt an automatic fix, or click Help to learn more. Use this tool every time you move a new workbook to Windows to help find potential problems.
Avoid Incompatible Attachments and Fonts
Excel on Windows can't open some of the image and video formats used in Excel for Mac. If you have any embedded images in the PICT format, replace them with PNG or JPG images. If your workbook uses QuickTime videos, replace them with MPG, MP4 or AVI videos.
To ensure your text looks the same on Windows, avoid fonts that aren't included with Windows. Compatible options include Arial, Times New Roman and Office's default font, Calibri.
Check Date Compatibility
Excel for Mac 2011 uses the same date system as Excel on Windows, the 1900 date system, which bases dates on the number of days since January 1, 1900. Older versions on Mac, however, use the 1904 date system, causing potential problems if you started a workbook on Excel for Mac 2008 or earlier. Dates won't show up incorrectly if you load the workbook in Windows, but they will copy incorrectly if you paste them in another file on a Windows computer.
To prevent dates from shifting by accident, let recipients know about this problem if you send workbooks that include dates to Windows computers. As a workaround, your recipients can rewrite dates in Windows-based workbooks rather than copying and pasting. They can also set Excel to use the 1904 system by checking Use 1904 Date System on the Advanced tab of Excel's Options window.