The standard Excel file extension is .xlsx

When you save a file in Microsoft Excel, it uses the .xlsx extension by default. This is the modern format that Excel has used since 2007. The "x" in .xlsx stands for XML, which is the underlying code structure that makes these files work. If you open a file and see .xlsx at the end of the name, you know it was created in a recent version of Excel.

The .xlsx format replaced an older format called .xls, which Excel used from 1997 to 2003. While .xls files still open in modern Excel, they lack some features and functions that newer versions support. Most people and organizations have moved to .xlsx because it handles larger spreadsheets, stores more data, and works better across different programs.

Key Takeaways

  • The .xlsx extension is the current standard for Excel files and has been since 2007.
  • The older .xls format still works but cannot store as much data or support as many features as .xlsx.
  • Excel also saves files in other formats like .csv, .xlsm, and .xltx depending on what you need the file to do.
  • The extension tells you what kind of file it is and which program should open it.
  • Changing a file's extension does not automatically convert it — you must save it in the new format through Excel's menu.

Why file extensions matter

A file extension is the short code at the end of a filename that tells your computer what kind of file it is and which program should open it. When you see a file named "Budget.xlsx", the .xlsx part is the extension. Your computer uses this to know that the file is an Excel spreadsheet and should open in Excel or a compatible program.

Without the extension, your computer would not know whether to open the file as a spreadsheet, a text document, or something else entirely. Extensions also help you quickly identify what you are looking at — a .xlsx file is always a spreadsheet, while a .docx file is always a Word document.

Common Excel file extensions and what they mean

.xlsx is the standard format for Excel workbooks. It stores all your data, formulas, and formatting. This is what you get when you open Excel and save a new file without changing the format.

.xls is the older Excel format from before 2007. Excel can still open and save in this format, but it has limits — it cannot store more than 65,536 rows or 256 columns, while .xlsx can handle over 1 million rows. If you work with older computers or need to share files with people using very old versions of Excel, you might save as .xls, but this is rare now.

.xlsm is an Excel file that contains macros — small programs or automated tasks that run inside the spreadsheet. If your spreadsheet has buttons that trigger actions or formulas that run automatically, it is likely saved as .xlsm. When you open an .xlsm file, Excel may ask whether you want to enable macros for security reasons.

.xltx is an Excel template file. Templates are pre-built spreadsheets with formatting, formulas, and structure already in place. When you open a template, Excel creates a new copy so you do not accidentally change the original. If you have a spreadsheet you use repeatedly with the same layout, you can save it as a template.

.csv stands for comma-separated values. This is a plain-text format that stores data in rows and columns separated by commas. Almost every program that handles data — including Google Sheets, Numbers on Mac, and many accounting programs — can open .csv files. Excel can save to .csv, but the file loses all formatting, colors, and formulas. Use .csv when you need to share data with a program that does not support Excel formats.

.ods is the OpenDocument Spreadsheet format used by free programs like LibreOffice Calc. Excel can open and save .ods files, making it useful when you work with people who use free or open-source software.

How to save a file in a different Excel format

To change what format your file is saved in, open the file in Excel and click File in the top left corner. Then click Save As. A window will open showing where you want to save the file and what name you want to give it.

Near the bottom of the Save As window, you will see a dropdown menu that says Save as type (on Windows) or File Format (on Mac). Click this dropdown to see all the formats Excel can save in. Select the format you want — such as .xls, .csv, or .xlsm — and then click Save. Excel will convert your file to that format and save it with the new extension.

If you simply rename a file by changing the extension — for example, changing "Budget.xlsx" to "Budget.xls" — the file does not actually convert. The computer will be confused about what format the file really is, and it may not open correctly. Always use the Save As method to properly convert between formats.

When to use each format

Use .xlsx for almost everything. It is the standard, works everywhere, and supports all modern Excel features. Unless you have a specific reason to use a different format, .xlsx is the right choice.

Use .xls only if you know the person receiving the file is using Excel 2003 or older, which is extremely rare. Most organizations have upgraded far beyond this.

Use .xlsm when your spreadsheet contains macros or automated tasks. Make sure the person opening it knows to enable macros, or the automated features will not work.

Use .csv when you need to share data with a program that does not support Excel, or when you need just the raw data without any formatting or formulas. Many online tools and databases accept .csv files.

Use .xltx when you have created a spreadsheet that you or others will use as a starting template repeatedly. Saving it as a template protects the original from accidental changes.

What happens when you open a file with the wrong program

If you try to open an Excel file with a program that does not recognize the format, one of several things can happen. The file might not open at all, or it might open but show garbled text and numbers that make no sense. Some programs will recognize the file but warn you that it may not display correctly.

This is why extensions matter — they tell your computer which program should open the file. If you have a .xlsx file and try to open it with Notepad (a plain text editor), you will see code instead of a spreadsheet. The file itself is fine; the program just is not designed to read that format.

Frequently Asked Questions

Can I change a file extension by renaming it?

You can rename the file and change the extension, but the file itself does not convert. The computer will be confused about what format the file actually is. Always use Excel's Save As feature to properly convert between formats.

What is the difference between .xlsx and .xlsm?

.xlsx is a standard Excel file with data, formulas, and formatting. .xlsm is the same thing but also contains macros — automated tasks or mini-programs that run inside the spreadsheet. If your file does not have macros, .xlsx is fine.

Can I open an Excel file in Google Sheets?

Yes. Google Sheets can open .xlsx, .xls, and .csv files. You can upload them to Google Drive or open them directly in Sheets. You can also save a Google Sheet as an Excel file to download it.

Why would I ever use .csv instead of .xlsx?

.csv is plain text that almost any program can read — accounting software, databases, websites, and tools that do not support Excel. Use .csv when you need to share data with a program that does not accept Excel formats, or when you only need the raw data without formatting.

Is .xls still used?

.xls is rarely used now because it cannot store as much data as .xlsx and lacks modern features. Some very old systems still require it, but most organizations switched to .xlsx years ago. If someone asks for .xls, ask whether they really need it or if .xlsx would work.