What a BAK file is and why your computer created it

A BAK file is a backup copy that software creates automatically when you edit a document or project file. When you open a file in most programs — whether it's a Word document, an Excel spreadsheet, a video project, or source code — the software saves the previous version with a .bak extension before overwriting the original. This happens silently in the background, and you usually never see it.

The BAK file sits in the same folder as your current file. It has the same name as the original, just with .bak at the end instead. For example, if you're editing a file called budget.xlsx, the program creates budget.xlsx.bak as a safety net. If something goes wrong — your computer crashes, you make a mistake you can't undo, or the file becomes corrupted — you can recover the version from before your last edit.

BAK files are not meant to be opened by you. They're meant to stay hidden and be used only if disaster strikes. But sometimes you need to access one deliberately, either because you want to recover an older version of your work or because you're cleaning up old files and want to know what you're deleting.

Key Takeaways

  • A BAK file is an automatic backup copy created by software before it overwrites your original file, stored in the same folder with the same name plus .bak at the end.
  • You can open a BAK file by renaming it to remove the .bak extension, then opening it with the same program that created the original file.
  • If renaming doesn't work, copy the BAK file, rename the copy, and try opening it with the program that originally created the file or a compatible alternative.
  • BAK files are safe to delete if you no longer need the backup, but keep them if you're unsure whether your current version is correct.

The simplest way: rename and open

The fastest way to open a BAK file is to rename it back to its original format. Find the BAK file in your file explorer or Finder, right-click it, and select "Rename". Delete the .bak extension — so budget.xlsx.bak becomes budget.xlsx — and press Enter. Then double-click the renamed file to open it in whatever program normally opens that file type.

This works because the .bak extension is just a label. The file itself is still the same format as the original — if it was an Excel file before, it's still an Excel file underneath. Removing the .bak label lets your computer recognize it as an Excel file again and open it with Excel or a compatible spreadsheet program.

If you're nervous about overwriting your current version, rename the BAK file to something different instead. For example, rename budget.xlsx.bak to budget_old.xlsx. This creates a separate file you can open and inspect without touching your current work.

When renaming doesn't work

Sometimes a BAK file won't open even after you rename it. This usually happens because the file is corrupted, or because it was created by a program you no longer have installed. If renaming fails, try these steps in order.

First, make a copy of the BAK file before you do anything else. Right-click it, select "Copy", then right-click in the same folder and select "Paste". Now you have a backup of the backup. Rename the copy to remove the .bak extension, then try opening it with the original program. If that program is no longer on your computer, try opening it with a similar program — for example, open a BAK file from a Word document with Google Docs, or open a BAK file from Photoshop with GIMP or another image editor.

If the file still won't open, the BAK file itself may be damaged. In that case, your current version is probably your best option. Delete the BAK file and move forward.

Understanding what program created the BAK file

The program that created the BAK file is usually the same one you need to open it with. If you're not sure which program created it, look at the original filename. A .bak file paired with a .docx file came from Microsoft Word. A .bak file paired with a .psd file came from Photoshop. A .bak file paired with a .py file came from a text editor or Python IDE.

If you don't have the original program installed anymore, you have two options. You can read and install the program again — many are free or have free trials. Or you can try opening the renamed BAK file with a different program that handles the same file type. For example, LibreOffice can open Word documents, GIMP can open Photoshop files, and Notepad can open files created by most text editors.

Some programs, like video editing software or specialized design tools, create BAK files that only their own software can read. If you no longer have that software and can't find a compatible alternative, the BAK file may not be recoverable. In that case, focus on your current version.

Deciding whether to keep or delete BAK files

BAK files take up disk space, but usually not much — most are the same size as the file they back up. If your hard drive is running low on space, deleting old BAK files is a safe way to free up room. They're meant to be temporary safety nets, not permanent archives.

Before you delete a BAK file, ask yourself: do I trust my current version? If you've been editing a file for weeks and you're confident the current version is correct, the BAK file from before your last edit is probably not useful. But if you're unsure whether your current version is right, or if you've made changes you regret, keep the BAK file for a few more days. Once you're certain the current version is good, delete the BAK.

If you're cleaning up and you see dozens of old BAK files from months ago, it's safe to delete them all. Your computer will create new ones the next time you edit files. The only BAK files worth keeping are the ones from recent edits to files you're still actively working on.

BAK files from different programs

Different software creates BAK files in slightly different ways, but the basic principle is the same: rename to remove the .bak extension, then open with the original program.

Microsoft Office (Word, Excel, PowerPoint) creates BAK files in the same folder as your document. Rename the BAK file to its original extension (.docx, .xlsx, .pptx) and open it with Office. Adobe programs like Photoshop and Premiere create BAK files the same way. Video editing software like DaVinci Resolve and Final Cut Pro also follow this pattern. Text editors and code editors create BAK files for source code and plain text files. The process is identical across all of them: rename and open.

Some older programs or specialized software may store BAK files in a different location or use a different naming convention. If you can't find the BAK file in the same folder as your original, check your program's preferences or settings menu for a "backup" or "recovery" option. The program's help documentation will tell you where it stores backups.

Recovering from a corrupted or lost file

If your current file is corrupted and won't open, a BAK file is your best recovery option. Rename the BAK file to remove the .bak extension and try opening it. If that works, you've recovered the version from before your last edit. You'll lose any changes made after that point, but you'll have your work back.

If the BAK file is also corrupted, check whether your program has a built-in recovery feature. Microsoft Office has a "Recover Unsaved Documents" option. Some other programs have similar features. Look in the File menu or Preferences for "Recovery", "Restore", or "Backup" options. These features sometimes store additional backup copies in a hidden folder on your computer.

If neither the BAK file nor the program's recovery feature works, you may need to accept the loss and move forward. This is why creating your own backups — separate from the automatic BAK files — is important for files you care about. Store copies on an external drive or cloud storage, not just on your computer.

Frequently Asked Questions

Can I open a BAK file without renaming it?

Not directly. Most programs won't recognize the .bak extension. You must rename it to its original format first. Some specialized recovery software can read BAK files without renaming, but renaming is simpler and works for almost all cases.

What if I rename a BAK file and it still won't open?

The file may be corrupted, or you may not have the correct program installed. Try opening it with a different program that handles the same file type — for example, use Google Docs to open a Word BAK file, or use GIMP to open a Photoshop BAK file. If nothing works, the BAK file is probably damaged.

Will opening a BAK file overwrite my current version?

Not if you rename it to a different name. If you rename budget.xlsx.bak to budget_old.xlsx, you create a separate file and your current budget.xlsx stays untouched. Only rename it back to the original name if you want to replace the current version.

How long do BAK files stay on my computer?

Until you delete them or until the program overwrites them. Most programs keep only the most recent BAK file for each document. When you edit the file again, the program replaces the old BAK with a new one. You can delete BAK files manually anytime.

Is it safe to delete all my BAK files?

Yes, as long as you're confident your current versions are correct. BAK files are temporary backups, not permanent archives. Delete them to free up space. Your computer will create new ones the next time you edit files. Only keep BAK files from recent edits if you're unsure about your current version.