"Your startup disk is almost full" on a Mac: free up space

Why it happens

The startup disk is your Mac's built-in drive, and macOS needs free room on it to work. When it's nearly full, apps slow down, updates won't install and files may fail to save. Usually a few big things fill it: videos, photo libraries, old downloads, phone backups or apps you no longer use.

How to fix it

1. Open the Apple menu, choose System Settings, click General, then Storage. Give the bar a few seconds to finish counting.

   General›Storage

2. Scroll down to the list of categories, which is sorted by size. Click the ⓘ next to the biggest ones, like Documents or Applications, to see what's inside.

3. In Documents, check Large Files and Downloads. Select anything you don't need and click Delete. Old installers, disk images and videos are usual suspects.

   General›Storage›Documents

4. Move large files you want to keep, like old videos or projects, to an external drive. Or use Store in iCloud, which keeps recent files on your Mac and older ones in iCloud. That uses your iCloud storage.

   General›Storage›Store in iCloud

5. Empty the Trash, because deleted files still use space until you do. Click the Finder menu and choose Empty Trash…, then confirm. If you deleted photos, also empty the Recently Deleted album in Photos.

   Finder›Empty Trash…

6. Restart your Mac, then check Storage again. Some space comes back only after a restart.

Still not fixed?

1. If System Data is huge, you can't clean it directly. Restart, leave your Mac plugged in for a while, and free space in the other categories. It often shrinks by itself.

2. Check iOS files for old iPhone or iPad backups. They can be many gigabytes each, and you can delete ones you no longer need.

   General›Storage›iOS files

3. Space marked purgeable is cleared by macOS when it needs the room. If you still see not enough space, deleting large files and restarting usually releases it.

4. The built-in drive on most modern Macs can't be upgraded later. If you're always full, an external drive or more iCloud storage is the practical answer.

5. If Storage still shows almost no free space after you've deleted a lot, run First Aid in Disk Utility. If that finds errors it can't repair, contact Apple Support or a repair shop, as the drive may have a hardware fault.

   Disk Utility›First Aid