Last Updated: 13 May, 2025
XLS and XLSX extensions represent popular Excel file formats that were introduced by Microsoft as part of its Office suite over a period of time. XLS being the oldest and widely used file type is also known to be the Excel97-2003 file format. The XLSX file format was introduced as a replacement of XLS file type with the launch of Excel 2007. Common users may not know the underlying differences between the two file formats, however, XLS is different than XLSX file format in several ways as detailed below.