Excel offers multiple file formats.
Pre-2007, all excel files were saved as .xls files.
Since 2007, there are a few other options, each with its own cost/benefit.
The nice people at AMT Training prepared the below chart. I’ve shown the first three file types. There are others, but they are less common.
|File extension||File format||Description||When to use|
|.xlsx||Excel Workbook||This is the main replacement for the former binary .xls format. For enhanced security, this format does not support Excel macros. Underlying this format is a ZIP archive of XML documents.||The default Excel format if macros are not used in your model.|
|.xlsm||Excel Macro-enabled Workbook||Exactly the same as .xlsx, but with the ability to support Excel macros.||The default Excel format if macros are used in your model.|
|.xlsb||Excel Binary Workbook||An Excel Macro-enabled Workbook. The file information is stored in binary format rather than as XML documents.||This file format is approximately twice as fast as .xlsx at opening and saving Excel Workbooks. This is particularly useful for very large files (greater than 10MB). This file extension can not be used by non-Excel applications such as Bloomberg and Capital IQ, so if these systems access your Excel file, then this file format should not be used.|