How to Recover an Excel Workbook from a .XLK Backup

You found 'Backup of <name>.xlk'. That is Excel's spare copy of your workbook. Here is how to open it.

Filename or extension

Category

Safe to delete?

Opens with

Open the .xlk in Excel

Open Excel and choose File → Open → Browse.
Set the file-type dropdown to All Files (*.*) so the .xlk is visible.
Select the Backup of ….xlk and open it. If Excel warns about the format, click Yes to open anyway — the contents are a standard workbook.
Save As a fresh .xlsx right away.

Alternative: rename a copy

You can also copy the .xlk and rename the copy to .xls or .xlsx, then double-click it. Rename a copy so the backup stays intact if the guess is wrong.

Where it lives and why

Excel writes the .xlk in the same folder as the workbook, named 'Backup of <name>'. It only appears when Save As → Tools → General Options → Always create backup is ticked. It is the version from your previous save, so it is your one-step-back safety net — not a live autosave.

FAQ

How do I open a .xlk file?

In Excel: File → Open → Browse with file type set to All Files, select the 'Backup of ....xlk', then Save As .xlsx. Or rename a copy to .xls/.xlsx and open it.

Where does Excel store .xlk backups?

In the same folder as the workbook, named 'Backup of <workbook name>.xlk'.

Excel says the file format is invalid — what now?

Click Yes/Open anyway; the .xlk is a normal workbook with a backup extension. If it still fails, use Open → Open and Repair.

Is it safe to delete a .xlk file?

Yes, when your main workbook is healthy; it only removes the one-save-behind spare copy.