macOS Startup Disk Almost Full Warning Fix

What Does This Error Mean?

The 'Your disk is almost full' warning means your Mac's main drive is running out of storage space. macOS needs free space to run properly — without it, your Mac slows down dramatically and may crash. You need to delete files, move data to an external drive, or buy more iCloud storage to fix this.

Affected Models

MacBook Air
MacBook Pro
iMac
Mac Mini
Mac Studio

Common Causes

Large files like videos, photos, and music have filled most of the drive
Time Machine local snapshots are consuming significant space
The Trash has never been emptied and contains gigabytes of deleted files
iPhone backups stored in iTunes or Finder are taking up large amounts of space
Downloaded files, app installers, and cached data have accumulated over time

How to Fix It

Use the built-in Storage Management tool. Go to Apple menu > About This Mac > More Info > Storage Settings. Click Recommendations to see Apple's suggestions for freeing space.

This tool shows exactly what is using your space and offers one-click options to enable iCloud optimization, empty the Trash, and remove large files.
Empty the Trash. Right-click the Trash icon in your Dock and click Empty Trash. Files in the Trash still take up space on your drive.

Many people delete files but never empty the Trash. It is common for the Trash to contain several gigabytes of old files.
Delete large files you do not need. Open Finder > Go > Home. Sort by size to find the biggest files. Look inside your Downloads folder, Desktop, and Documents for large files you no longer need.

Videos are usually the biggest space users. Even one downloaded movie can be 4 to 10 GB.
Delete old iPhone backups. Open Finder and click on your iPhone in the sidebar (if connected). Or go to System Settings > General > iPhone Storage to manage backups stored on your Mac.

iPhone backups can be several gigabytes each. If you back up to iCloud instead, you do not need local backups on your Mac.
Move photos to iCloud or an external drive. Open Photos app > Settings > iCloud and turn on iCloud Photos. This stores full-resolution photos in iCloud and keeps smaller previews on your Mac.

A large photo library can easily take 50 to 200 GB. Moving it to iCloud is one of the fastest ways to reclaim space.

When to Call a Professional

You do not need professional help for a full disk — this is something you can fix at home. However, if you need more storage permanently, an Apple Store can discuss your options. On MacBooks, the internal SSD cannot be upgraded after purchase — your only options are external drives or iCloud.

Frequently Asked Questions

How much free space does my Mac need to run well?

Apple recommends keeping at least 10 to 15% of your total disk capacity free. For example, on a 256 GB Mac, try to keep at least 25 to 40 GB free. When the drive is nearly full, macOS cannot create the temporary files it needs and slows down significantly.

What are Time Machine local snapshots and can I delete them?

When Time Machine cannot reach its backup drive, it saves temporary backups (called local snapshots) to your internal drive. These can grow to take up tens of gigabytes. macOS automatically deletes them when you need space, but you can also delete them manually via Terminal.

Can I add more storage to my MacBook?

No — on all modern MacBooks, the SSD is soldered to the motherboard and cannot be upgraded or replaced. Your options are: use iCloud for cloud storage, use an external USB-C or Thunderbolt drive, or buy a Mac with more storage next time.