If you plan to share your workbook with users who have different versions of Excel, and you don't mind a larger file size, the most versatile Excel file format is the Microsoft Excel 97-2002 & 5.0/95 Workbook format. This format saves two versions of a workbook (one with the Microsoft Excel 97-2002 file format and one with the Microsoft Excel 5.0/95 file format) in the same .xls file. Users of Excel 2002 can continue to work in the workbook and use any of the features or formatting unique to this version. Users of Microsoft Excel version 5.0 or Microsoft Excel 95 can open and use the workbook without having to convert the file.

It is recommended that users with older versions use the workbook read-only. If the workbook is saved in the earlier version of Microsoft Excel, features and formatting unique to the current version will be lost.