Software & Apps File Types Excel File Extensions and Their Uses XLS, XLSX, XLSM, XLTX and XLTM By Ted French Writer Former Lifewire writer Ted French is a Microsoft Certified Professional who teaches and writes about spreadsheets and spreadsheet programs. our editorial process Ted French Updated November 14, 2019 File Types Design Cryptocurrency MS Office Windows Linux Google Drive Apps File Types Backup & Utilities View More Tweet Share Email A file extension is the group of letters that appear after the last period in a file name. File extensions are 2 to 4 characters long and the format. Let's learn about the different types of file extensions that Excel uses and see how to change files from one format to another. The information in this article applies to Excel 2019, Excel 2016, Excel 2013, Excel 2010, Excel 2007, Excel Online, and Excel for Mac. XLS vs. XLSX The current default file extension for an Excel file is XLSX. Prior to Excel 2007, the default file extension was XLS. The main difference between the two is that XLSX is an XML-based open file format and XLS is a proprietary Microsoft format. But, the newer versions of Excel save and open XLS files for the sake of compatibility with earlier versions of the program. Determine if a file contains macros before you open it. Macros may contain malicious code that can damage files and compromise computer security. Excel files containing VBA and XLM macros use the XLSM extension. XML and HTML XML stands for extensible markup language. XML is related to HTML (hypertext markup language), the extension used for web pages. Advantages of this file format include: Smaller file sizes for storage and transfer.Better recovery of information from damaged files.Easier detection of files containing macros. XLTX and XLTM If an Excel file has either an XLTX or an XLTM extension, it is saved as a template file. Template files are used as starter files for new workbooks. Templates contain saved settings such as the default number of sheets per workbook, formatting, formulas, graphics, and custom toolbars. The difference between the two extensions is that the XLTM format can store VBA and XML macro code. Excel for Mac Macintosh computers do not rely on file extensions to determine which program to use when opening a file. However, for the sake of compatibility with the Windows version of the program, Excel for Mac uses the XLSX file extension. Excel files created in one operating system can be opened the other. One exception to this is Excel 2008 for the Mac, which does not support VBA macros. As a result, it cannot open XLMX or XMLT files created by Windows or later Mac versions that support VBA macros. Change File Formats With Save As To change an Excel format (and its extension), follow these steps: Open the workbook that you want to save in a different file format. Select File. Select Save As. Except in Excel 2019, where you select Save a Copy. In the dialog box, accept the suggested file name or type a new name for the workbook. In the Save as type or File Format list, choose the file format you want to use to save the file. Select Save to save the file in the new format and return to the current worksheet. If a file is saved in a format that does not support all the features of the current format, such as formatting or formulas, an alert message box appears. You're given the option to cancel and return to the Save As dialog box.