Mac Storage Full? How to Fix "Startup Disk Almost Full"

Why the "Startup Disk Almost Full" Warning Appears

macOS shows this warning when free space on your startup disk drops into single-digit gigabytes. It matters for more than storage: macOS uses free disk space as virtual memory (swap), so a nearly full drive doesn't just stop you saving files — it makes the entire system slow, causes apps to hang, and can prevent macOS updates from installing.

The fix is to reclaim space, and the smart approach is to start with the categories that give you the most gigabytes for the least effort. That's how this guide is ordered.

The Fastest Wins, in Order

Work down this list top to bottom. The first few steps typically recover the most space in the least time.

1. Empty the Trash. Files you've "deleted" still occupy space until the Trash is emptied. Right-click the Trash icon and choose Empty Trash. This alone can recover several gigabytes instantly.
2. Clear out Downloads. The Downloads folder is where forgotten installers, .dmg files, and huge attachments pile up. Sort it by size in Finder and delete what you no longer need.
3. Delete app caches. Caches in ~/Library/Caches are often the single biggest slice of reclaimable space — commonly 10 GB or more. Apps rebuild them automatically, so clearing them is safe.
4. Find and remove large files. Use Storage > the "Large Files" review, or a storage analyzer, to surface forgotten multi-gigabyte videos, disk images, and old archives.
5. Delete duplicate files. Duplicated photos, downloads, and documents quietly waste space. A duplicate finder can reclaim gigabytes you didn't know were doubled up.
6. Remove old backups and snapshots. Time Machine local snapshots and old iOS device backups can occupy huge amounts of space on your startup disk.

Step 1 & 2: Trash and Downloads (Biggest Instant Wins)

Start where the space is easiest to reclaim. Emptying the Trash is instant and often frees more than people expect, because large files you deleted are still sitting there. Then open your Downloads folder, switch to list view, and click the Size column. You'll almost always find old installers, disk images, video files, and giant email attachments you downloaded once and forgot. Delete them and empty the Trash again.

Don't overlook other Trash cans, either — the Photos app and Mail keep their own "Recently Deleted" areas that hold onto files until you empty them separately.

Step 3: Clear Caches and System Junk

After the obvious files, caches are the highest-value target. App caches live in ~/Library/Caches and can total tens of gigabytes on a Mac that's been in use for a year or more. They're safe to remove because apps regenerate them on demand. For the full walkthrough, see our guide on clearing app cache on Mac. Logs and other temporary files add a smaller but worthwhile amount on top.

Step 4 & 5: Large Files and Duplicates

Once the quick wins are done, hunt down the space hogs. Large forgotten files — old video projects, VM images, downloaded ISOs, and unused app bundles — are frequently the reason a disk fills up. macOS has a built-in "Review Large Files" option in the Storage screen, but a dedicated storage analyzer gives you a clearer, drillable map of where every gigabyte lives.

Duplicates are the sneakier culprit. The same photo saved twice, a document downloaded three times, or duplicated media libraries can waste gigabytes without you noticing. A duplicate file finder compares file contents and lets you safely remove the redundant copies while keeping one of each.

Step 6: Old Backups and Snapshots

Two backup-related sources can occupy surprising amounts of your startup disk. First, Time Machine keeps local snapshots on the internal drive so you can restore even without your backup drive connected — these normally thin out automatically but can spike after big changes. Second, if you've ever backed up an iPhone or iPad to your Mac, those device backups can be many gigabytes and are easy to forget.

Local snapshots can be thinned with tmutil in Terminal, and old device backups can be deleted from the Finder (for a connected device) or from within the Storage management screen. Remove backups you no longer need, but keep at least one current backup of anything important.

Do It All in One Pass with TrimyMac

Working through six categories by hand takes time and care. TrimyMac collapses the whole process: its Smart Clean scans your disk in seconds, itemises the reclaimable caches, logs, and Trash, and clears them in one click — while its analyzer and duplicate finder surface the large and doubled-up files that manual methods miss. It's the fastest way to go from "startup disk almost full" back to comfortable free space.