Syntic Care

Troubleshooting · Mac

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

Updated 2026-10-03 · By Syntic Care Team · Reviewed by Diana · Director

Short answer

The warning means the disk your Mac starts up from is nearly out of space. Open System Settings › General › Storage to see which category is largest, then work in this order: empty the Trash, review your Downloads folder, find large files, remove old iPhone and iPad backups you no longer need, uninstall apps you don't use, and consider Apple's Store in iCloud, Optimize Storage and Empty Trash Automatically options. Check each item before you delete it, and never delete system folders.

What the warning means

Your startup disk is the drive your Mac starts up from, usually called Macintosh HD. When it gets low on space, macOS warns you. Depending on the situation, the message reads "Your startup disk is almost full", "Your startup disk is full" or "Your disk is almost full". When there's no space left, there's no room to save new files or install updates.

There's no single fix, because "full" can mean very different things on different Macs:

  • Your own files: videos, photos, downloads, music libraries, projects.
  • Apps and their data: large apps, plus data they keep in your Library folder.
  • Device backups: full iPhone or iPad backups made to this Mac.
  • System Data: the catch-all category for files that don't belong to any named category.

Your first job is to find out which of these is the big one. Deleting things at random wastes time, and it's how people lose files they wanted to keep.

Free up space with macOS, in a sensible order

These steps use the System Settings layout from macOS Ventura 13 onwards, including macOS 27.

1. See what's using the space

Choose Apple menu › System Settings, click General, then click Storage. Wait for the bar to finish calculating. Each category is listed with its size, and the Info button (the small i) next to a category opens more detail.

If System Data is the largest category, the steps below still help, but read why System Data is so large for what's inside it.

2. Empty the Trash

Files you delete stay in the Trash, still using space, until you empty it. Control-click the Trash in the Dock and choose Empty Trash. Before you do, open the Trash and make sure there's nothing in it you want back.

3. Review your Downloads folder

In Finder, choose Go › Downloads, switch to View › as List and sort by Size. Installers, disk images and archives you've already used are often in here. Open anything you don't recognise before you decide, and move what you don't need to the Trash.

4. Find large files

In Storage settings, click the Info button next to Documents and open Large Files. For anything outside your own documents, use a Finder search with a File Size rule. How to find large files on your Mac covers each method step by step. Move videos and archives you want to keep to an external drive.

5. Review iPhone and iPad backups

If an iOS Files category appears in Storage settings, click its Info button to see the device backups and software update files stored on this Mac, with their dates. Delete a backup only when it belongs to a device you no longer own, or when a newer backup of the same device exists.

6. Uninstall apps you don't use

Click the Info button next to Applications to see your apps and their sizes. Remove the ones you no longer need. You can download App Store apps again at any time.

If you build software, developer tools can take a lot of space: see how to clear Xcode DerivedData.

7. Consider Apple's storage options

At the top of Storage settings, macOS may offer:

  • Store in iCloud: keeps Desktop and Documents files, photos and messages in iCloud, and keeps only recent files and optimized photos on your Mac when space is needed. This uses your iCloud storage.
  • Optimize Storage: removes Apple TV movies and TV shows you've already watched, and keeps only recent email attachments on this Mac when space is needed.
  • Empty Trash Automatically: erases items that have been in the Trash for more than 30 days.

macOS also clears some caches and logs that are safe to delete by itself.

What not to delete

  • Deleting in Storage settings is permanent. macOS warns that items are deleted immediately and that you can't undo this. If you want a way back, show the file in Finder and move it to the Trash instead.
  • Never delete files in /System, /Library or /private, or files inside app bundles. Your Mac needs them to start up and run.
  • A large file isn't automatically safe to delete. Before you delete a device backup, a photo library or a project, make sure a copy exists somewhere else.
  • Understand iCloud before you delete. If your Desktop and Documents folders are in iCloud Drive, deleting a file on your Mac deletes it on every device signed in to the same Apple Account. To keep a file but get it off this Mac, move it to an external drive.
  • Don't rely on deleting caches. Apps rebuild their caches as you use them, so the space comes back.
  • Leave some free space. macOS needs room for updates and temporary files, so don't run the disk right up to its limit.
  • Back up before a big cleanup, with Time Machine or another backup method.

The Syntic Care method

Syntic Care's storage overview and Disk Analyzer show what is using space on your Mac. You can see it by category or as a map you explore folder by folder, so you know where the space went before you decide what to remove. Syntic Care shows and explains what it finds. It does not delete anything.

Syntic Care for Mac version 1 shows and explains what it finds. Actions that would change your Mac are not available yet.

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