A .bak file is a backup copy your computer makes automatically, usually when you edit or save over an original file

When you open a document in certain programs — particularly older text editors, spreadsheet applications, or development tools — and then save changes to it, the program often creates a second file with the same name but ending in .bak instead of the original extension. That .bak file holds the version of the document as it existed before you made your latest changes. It sits in the same folder as your current file, taking up disk space, and most people never notice it exists.

The .bak extension stands for "backup". The program creates it as a safety net: if you save changes you later regret, or if something corrupts your main file, you have a copy of the previous version to fall back on. You do not ask the program to make it. It happens in the background, usually without any notification.

Key Takeaways

  • A .bak file is an automatic backup of the previous version of a document, created by certain programs when you save over the original.
  • Not all programs create .bak files — Microsoft Word and Google Docs do not, but many text editors and older software do.
  • You can safely delete .bak files if you no longer need the old versions, though keeping them takes up only small amounts of storage.
  • .bak files are hidden by default on most computers, so you may need to change your folder settings to see them.
  • If you want to recover an older version of a document, you can rename the .bak file to restore it as your working copy.

Which programs create .bak files

Older software and specialized tools are the main creators. Text editors like Notepad++, Sublime Text, and gedit often create .bak files by default. Many programming environments do the same. Some spreadsheet programs, particularly older versions of Excel or LibreOffice Calc, will generate them. Accounting software and database tools frequently use .bak as well.

Modern programs like Microsoft Word, Google Docs, and Adobe Creative Suite do not create .bak files in this way. Instead, they use their own backup systems — Word saves versions in a recovery folder, Google Docs saves automatically to the cloud, and Adobe programs use their own versioning. If you work mostly in newer software, you may never encounter a .bak file at all.

Why .bak files are usually invisible

Operating systems hide .bak files by default because they are meant to be background safety copies, not files you interact with regularly. On Windows, you can reveal them by opening File Explorer, clicking the View tab, and checking "Hidden items". On Mac, you can use Finder's View menu and select "Show Hidden Files", or press Command+Shift+Period. On Linux, most file managers have a View option to show hidden files, or you can use the keyboard shortcut Ctrl+H.

Once you turn on the visibility of hidden files, you will see .bak files sitting alongside your regular documents. They look like ordinary files with a slightly faded icon in many systems. If you turn the setting back off, they disappear from view again — they are still there, just not displayed.

How much space .bak files actually use

A single .bak file takes up roughly the same amount of disk space as the document it backs up. A small text file might generate a .bak file of a few kilobytes. A large spreadsheet could create a .bak file of several megabytes. If you edit a document once and never touch it again, you have one .bak file. If you edit it ten times in a day, you have one .bak file — the program overwrites the old backup each time you save, so you never accumulate dozens of them.

For most people, .bak files consume negligible storage. Unless you work with very large files and edit them constantly, or you have thousands of documents, the total space used by .bak files will be a rounding error on your hard drive. Modern computers have hundreds of gigabytes or terabytes of storage, so a few dozen .bak files matter very little.

When you might want to keep a .bak file

If you made changes to a document and then realized you deleted something important, the .bak file holds the previous version. You can rename it to restore it as your working copy. For example, if you have a file called budget.xlsx and its backup budget.bak, you could rename the .bak file back to budget.xlsx and open it to see what the spreadsheet looked like before your latest edits.

This is most useful in situations where you do not have other version history. If you use a program that does not offer undo, or if you closed the document and cannot undo anymore, the .bak file may be your only way to recover an earlier state. For work files or documents you edit frequently, keeping .bak files costs almost nothing and provides a safety margin.

When you can safely delete .bak files

If you are confident you will not need to revert to an earlier version of a document, you can delete its .bak file without any consequence. The .bak file does not affect the current version of your document — deleting it only removes the backup. Your working file stays exactly as it is.

You can delete individual .bak files by right-clicking and selecting Delete, or you can select multiple .bak files at once and delete them in bulk. Some people delete all .bak files periodically to keep their folders tidy. Others leave them alone because the storage cost is minimal. There is no right answer — it depends on how much clutter bothers you and how much you value having a quick way to revert to a previous version.

How to prevent .bak files from being created

Most programs that create .bak files offer a setting to turn the feature off. In a text editor like Notepad++, you would go to Settings or Preferences, find the Backup option, and disable it. In LibreOffice, you go to Tools, Options, Load/Save, and uncheck "Always create backup copy". The exact path varies by program, but the setting usually lives in Preferences, Settings, or Options.

If you disable .bak file creation, the program will no longer make backups when you save. This frees up a tiny amount of disk space and removes the clutter, but you lose the safety net of having a previous version available. For most users, the benefit of keeping the feature on outweighs the minimal storage cost, but the choice is yours to make in each program you use.

Frequently Asked Questions

Can I delete a .bak file while the document is open?

Yes. The .bak file is separate from your working document, so deleting it will not affect the file you are currently editing. The program may create a new .bak file the next time you save, depending on its settings.

What if I see a .bak file but do not know what document it came from?

The .bak file has the same name as the original document, just with .bak at the end instead of the original extension. If you see report.bak, it is the backup of report (which might be report.txt, report.docx, or another format). You can rename it to see what it contains.

Is a .bak file the same as a cloud backup?

No. A .bak file is a local backup stored on your computer in the same folder as your document. Cloud backups like OneDrive, Google Drive, or iCloud store copies on remote servers. A .bak file protects you from accidental edits; cloud backups protect you from hardware failure or device loss.

Why does my program create a .bak file every time I save, but I only see one?

The program overwrites the old .bak file each time you save. So if you edit a document five times, you still have only one .bak file — the backup of the version from your most recent save. You do not accumulate multiple backups this way.