Is it safe to delete Windows.old?

Yes, it's safe to delete Windows.old, as long as you're happy with your current version of Windows and don't plan to go back. Windows.old is the backup of your previous installation. Your running Windows doesn't need it, and Windows removes it by itself after ten days anyway. Deleting it early frees the space now, but the rollback option goes with it.

Quick verdict:

• Safe: deleting Windows.old once the upgrade works and you've copied out any personal files you still need.
• Wait: if the upgrade is only a few days old and something still feels off (drivers, an app, a printer).
• Use the right tool: Settings or Disk Cleanup, not File Explorer.
• Not undoable: once it's gone, you can't go back to the previous version of Windows.

What is Windows.old?

C:\Windows.old is created by Windows Setup when you upgrade to a new version of Windows: from Windows 10 to Windows 11, from one yearly Windows 11 version to the next, or during a repair install that keeps your files. Setup moves the previous installation into this folder instead of throwing it away.

It holds the old Windows folder, the old Program Files, and the old user profiles under C:\Windows.old\Users. That's what makes Settings → System → Recovery → Go back possible. According to Microsoft, going back needs everything in windows.old and $windows.~bt to still be there, and in most cases you have ten days to do it.

After those ten days, Windows deletes the previous version automatically. So if you find Windows.old long after an upgrade, it may simply be from a recent one, or the automatic cleanup hasn't run yet.

How much space does it use?

Windows.old is a copy of a whole Windows installation plus whatever was in the old program and user folders, so it usually takes many gigabytes. To see the exact figure:

• Settings → System → Storage → Temporary files: the line Previous Windows installation(s) shows its size.
• Disk Cleanup: after you click Clean up system files, the same entry appears with its size.

To see where it sits next to everything else on the drive, scan C: with SquirrelDisk. Windows.old shows up as one big slice at the root of the drive, and you can click it to look inside, for example at Users to check what personal files are still in there. SquirrelDisk runs without administrator rights, so parts of the folder your account can't read are skipped, and the size may show a little smaller than the Settings figure.

How to delete it safely

Before you start: rescue your files

When the upgrade kept your files, there's usually nothing personal left in Windows.old that you don't already have. But if you did a clean install, or something went missing, check first:

1. Open File Explorer and go to C:\Windows.old\Users\<your name>.
2. Look in Documents, Desktop, Pictures, Downloads and other folders you used.
3. Copy anything you want to keep to your current user folder or to an external drive.

Once Windows.old is deleted, these copies are gone for good.

With Settings (Windows 11 and 10)

1. Open Settings → System → Storage.
2. Select Temporary files. Windows needs a moment to calculate the sizes.
3. Tick Previous Windows installation(s). Untick anything else you don't want removed, such as Downloads.
4. Select Remove files and confirm.

On Windows 11 you can also find the same entry under Storage → Cleanup recommendations. You need an administrator account for this.

With Disk Cleanup

1. Press Start, type Disk Cleanup and open it. Pick drive C: if asked.
2. Click Clean up system files. Disk Cleanup scans again with administrator rights.
3. Tick Previous Windows installation(s) and click OK, then Delete Files.

The removal can take several minutes. Restart afterwards if a few files remain.

Why not just delete the folder?

Many files inside Windows.old belong to the system, not to your account. File Explorer will ask for permissions, stop halfway, or leave a folder you can't remove. Taking ownership of everything works, but it's slow and easy to get wrong. The built-in cleanup does the same job properly, so there's no reason to fight Explorer, or to use a third-party tool for it.

What you should not delete

• Windows.old in the first days after an upgrade, if you're not sure yet. Check that drivers, printers, VPN clients and the apps you rely on all work.
• C:\$Windows.~BT while you might still go back: Microsoft lists them as needed for the rollback. Settings and Disk Cleanup remove them for you when they're no longer needed.
• Your current C:\Windows folder. It's easy to mix the two up in a long list of folders. Windows.old has .old in the name; the other one is the Windows you're running.

If you delete Windows.old and later want the old version back, the only way is a clean install of that version from installation media, followed by restoring your files from a backup.

Need more time to decide?

If the ten days are almost up and you're still not sure, you can extend the rollback window. Open Terminal (Admin) and run:

DISM /Online /Get-OSUninstallWindow
DISM /Online /Set-OSUninstallWindow /Value:30

The first command shows the current number of days, the second sets it to 30. Microsoft's DISM documentation says any value from 2 to 60 works; outside that range Windows uses the default of 10. It only works while the previous version still exists.

Better ways to free space

Windows.old is usually the biggest single win after an upgrade, but the same Temporary files page also lists Windows Update Cleanup and Delivery Optimization Files. See is it safe to delete the SoftwareDistribution folder and Delivery Optimization files for those. For everything else, a scan with SquirrelDisk shows which folders actually take the space, so you can decide what's worth removing.