Can I delete the Windows.old folder?

Short answer: Windows.old is your previous Windows, kept after an upgrade so you can go back. It is often 10 to 30 GB. Windows removes it by itself after about 10 days. If you are happy with the new version, you can remove it sooner.

By hand, with Windows' own tools

Open Settings > System > Storage > Temporary files.
Tick Previous Windows installation(s) and choose Remove files.

With Sparewise

Shows the size of the previous Windows and how many days it has left.
Points to the Windows setting that removes it safely.

Questions

What happens if I delete Windows.old?

You can no longer go back to the previous version of Windows. Your files and apps in the current Windows are not affected.

Get Sparewise, free

Get it from the Microsoft Store or download the installer

Free · Windows 10 and 11 · No account · No telemetry · Everything it removes can be put back

More guides: all guides