Troubleshooting guide for the file format and extension don't match error

Microsoft Excel is probably the most used spreadsheet tool in the world.

The guide below will show you how to handle File format and extension issues in Excel.

To read more about this amazing tool, visit our Excel Hub.

For more MS Office-related tutorials, check out our Microsoft Office How-To page.

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If you rename a file extension from one Excel format to another (e.g., from a .xlsx to .xls), you get the following error message:

The file format and extension of .xls don’t match. The file could be corrupted or unsafe. Unless you trust its source, don’t open it. Do you want to open it anyway?

Microsoft Excel opens files in various formats, such as .xls, .xlsx, .xlsm, .xlsb, .xltx, .xml, and many more. This error also gets worse. If you click Yes, the file opens anyway, but with all of its content missing.

Of course, like all error messages, the format and extension don’t match error can be as a result of other underlying issues, the most common of which is that the document is deemed to be corrupt.

Here is what to do when faced with this challenge.

How do I fix the file format and extension match error?

1. Unblock access for safe files

Go to the folder which contains the Excel file.

Right-click on the document you are trying to open.

From the options, select Properties.

Next, on the General tab hit Unblock.

Finally, click on the OK.

2. Add the workbook to a Trusted Location

Launch Ms Excel.

Click File on the toolbar and then choose Options.

Next, in the resulting screen, click Trust Center.

fix file format and extension don't match: click trust center

Finally, click on Trust Center Settings and select Trusted Locations on the left sidebar.

add a trusted location to repair the file format and extension don't match error

In Microsoft Excel 2010, 2013, and 2016, saving a file to a Trusted Location lets the program view it as safe. Excel comes with default trust locations, and you can add others by clicking the Add new location button.

Save the problematic worksheet in a trust location and try to open it again. However, you must note that if a malicious person places a file in a trusted location, Excel will overlook this document also.

3. Repair the workbook to fix file format and extension don’t match error

Launch Microsoft Excel.

Click the File menu on the toolbar and hit Open.

This will open the dialog box to browse for the file.

From the dialog box, click Browse and find the workbook that gives the file format and extension don’t match.

Next, instead of opening this file straight away, click on the little arrow beside the Open button and choose the Open and Repair option from the dropdown.

open and repair worksheet to fix file format and extension don't match error

Finally, click Repair. This should now recover the content of the problematic workbook.

If the Repair operation fails to restore all the formulas and values from the workbook, try again by using the Extract Data

These solutions above should clear the file format and extension don’t match error. However, if all fail, backing up the workbook or creating a recovery file can salvage your data.

In the next section, we will explore how to recover data from the problematic file, as well as how to back up the workbook.

4. Change the calculation setting to manual from automatic

Launch Microsoft Excel.

Click on the File menu on the toolbar and hit New.

Next, click on Blank workbook. This will open a new workbook with no values.

Now, click on file again, but this time, select Options.

Navigate to Formulas, and under Calculation options, select Manual.

manual formula calculation fixes file format and extension don't match error

Hit OK.

Now open the workbook and confirm that the file no longer gives the file format and extension don’t march error or opens blank sheets.

In conclusion, the file format and extension don’t march error comes, especially when you rename an Excel file to another extension.

We have looked into troubleshooting this issue by unblocking files, saving and opening the workbook from a trusted location, and repairing the file.

Also, we went over preventive measures to take on your worksheet, so that you do not lose data. Are you experiencing this issue or got it in the past? How did you resolve it?

We appreciate your comments and will get to as many as possible.