Mac startup disk full? Here’s how to fix it

💡 Need to know

• A full startup disk affects more than storage: Low space can slow your Mac, block updates, and cause apps to crash unexpectedly.
• The biggest storage hogs may surprise you: Videos, downloads, backups, and system data often take up more space than apps.
• Deleting files isn't always enough: Items in the Trash and temporary system files can continue using storage behind the scenes.
• Don't fill your drive to 100%: macOS needs free space to run smoothly, so keeping some storage available is important for performance.

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You turn on your Mac® like you do every day, only this time it's giving you a somewhat ominous message: “Your startup disk is almost full."

Don't worry—but don't ignore the message either. At Asurion, we take care of you and your tech. We'll walk you through what to do right away to free up startup disk space on Mac.

What is a startup disk?

The startup disk is the primary partition where your macOS system files, application packages, and personal user data live. It contains all the underlying instructions your computer needs to turn on and run its software. Usually, the startup disk is your built-in internal solid-state drive, known natively as Macintosh HD.

What does a full startup disk mean?

When your startup disk is full, it means your Mac is running out of the storage space needed for your computer to load and work properly.

So if you get a startup disk error message, the best thing you can do is act fast. We'll walk you through the process.

How to check the disk storage on your Mac

Your Mac can show you exactly what file types are hoarding your space, making it easy to decide what to clean up first.

1. Click the Apple menu icon in the top-left corner of your screen.
2. Select System Settings > General > Storage.
3. Look at the color-coded bar chart at the top of the window to see exactly how much room is being consumed by Applications, Documents, System Data, or iCloud Drive files.

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How to free up disk space on your Mac

Now that you you know what's taking up all that space, let's go over the ways to free some of it up.

Store large computer files on the cloud or on an external hard drive

Backing up your Mac's largest files is the easiest—and fastest—way to free up disk space. There are two main ways to do so.

1. Save files to the cloud. iCloud® is a quick, easy, and secure way to move bigger files off your computer and onto a secure data server for storage. Your files will be there whenever you need them again, so long as you can access the internet.
2. Use an external hard drive. If cloud storage isn't for you, try moving your photos and videos to an external drive. These files usually take up the most space, so moving them will save you the hassle of having to go through all your documents.

Delete unwanted files, apps, and backups

Do you really need everything on your computer? What brings you joy? Marie Kondo your Mac and get rid of extraneous data to enjoy more storage space. That could mean old photos, videos, apps, and documents. Or it could mean everything you backed up from that iPhone® 6 you had nearly a decade ago. We'll walk you through how.

How to find your largest files

Deleting your largest files will help you make space on your Mac—fast. Here's how:

• On macOS® Ventura or later: Go to the Apple menu > System Settings. Click General in the sidebar, then click Storage on the right.
• On earlier versions of macOS: Go to the Apple menu > About This Mac, then click Storage.

Now you're ready to sift through your largest files and delete them.

How to delete old backups

Your old backups may be among your largest files. Here's how to get rid of them:

On macOS® Ventura or later:

1. Go to the Apple menu > System Settings > General > Storage.
2. Scroll past the storage bar chart down to the category breakdown list.
3. Locate the iOS Files row (this is where old iPhone and iPad backups live).
4. Click the small "i" (Information) icon at the far-right end of that row.
5. Select your outdated backup from the pop-up list and click Delete.

On earlier versions of macOS:

1. Go to the Apple menu > About This Mac, then click Storage.
2. Click Manage. Then, select iOS Files.
3. Click the old backup and delete it. Click Remove to permanently erase it from the MacBook.

How to delete apps you don't use

If you don't use some of your apps, get rid of them.

1. Click the Finder icon in the Dock.
2. Click Applications in the Finder sidebar.
3. Depending on the location of the app, you might have some different steps to follow. Don't worry—we've got steps for both cases.

If an app is in a folder: Open the app's folder to check for an Uninstaller. If Uninstall or Uninstaller appears, double-click it, then follow the instructions on the screen.

If an app isn't in a folder or doesn't have an Uninstaller: Drag the app from the Applications folder to the Trash.

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My Mac says there's not enough disk space, but there is

What if you have ample space and still see that error message? Your iCloud may be using a portion of your storage as a placeholder. This often occurs if you've turned on a setting called iCloud Drive.

To turn off that setting and get the most out of the space you have, try the following steps:

1. Click the Apple icon > System Settings.
2. Click the Apple ID, then select iCloud.
3. Turn Optimize Mac Storage off.

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What to do if your Mac crashes or won't boot due to a full disk

If your Mac has already begun its “startup disc full" death spiral, you have one last thing to try—turning on Safe Mode. This may free up enough space to allow it to start.

How to boot into Safe Mode

Shut your Mac down completely. The method to trigger Safe Mode depends entirely on what processor chips power your computer:

For modern Macs (Apple Silicon M1, M2, M3, M4, or newer):

1. Press and hold down the physical Power button on your keyboard. Keep holding it until the display says "Loading startup options..."
2. Select your primary hard drive (Macintosh HD).
3. Next, press and hold the keyboard Shift key, and click Continue in Safe Mode.

For older Macs (Intel-based, 2020 and earlier):

Turn your Mac back on and immediately press and hold down the keyboard Shift key. Keep holding it until you see the Apple logo and a login window appear.

If Safe Mode works, start moving or copying your personal data to the cloud or an external hard drive. You'll want to save as much as you can before it's gone.

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FAQ

What does "startup disk full" mean on a Mac?

It means your Mac's main storage drive is nearly out of available space, which can affect performance, updates, and app functionality.

How much free space should my Mac have?

A good rule of thumb is to keep at least 10–20% of your storage free so macOS has room for temporary files and system tasks.

Why is my Mac still full after deleting files?

Deleted files may still be in the Trash, or storage could be tied up by caches, backups, downloads, and system data that aren't immediately obvious.

Can a full startup disk make my Mac slower?

Yes. When storage gets too low, your Mac can become sluggish, apps may freeze, and system updates may fail.

How do I see what's taking up space on my Mac?

Go to System Settings > General > Storage to view a breakdown of how your storage is being used and identify the biggest space hogs.