5. Files, Formats and Saving

• .xlsx — the standard Excel workbook, the main format;
• .xlsm — a workbook with VBA macros. Only open such files from people you trust: a macro is a program;
• .xlsb — a binary workbook: it opens faster and is smaller, which suits very large files;
• .csv — plain text with values separated by a delimiter. Formulas, formatting and worksheets are not saved in it;
• .ods — the LibreOffice/OpenOffice format.

AutoSave works for files stored on OneDrive or SharePoint. For files on your computer, save them yourself (Ctrl+S), and after a crash look for unsaved versions under File › Info › Manage Workbook.

Give files clear names that start with the date: 2026-03_Sales_Chicago.xlsx. That way they sort by time.