Why your Mac fills up faster than you put anything on it
Why Mac storage keeps filling up after you delete things: snapshots, caches, iCloud downloads and Recently Deleted, and how to find which one it is.
The computer gets fuller the more I use it, and the most ridiculous part is when I open up storage and see: "System Data" taking up dozens of GB, yet I have no idea what it actually is.
Why does my Mac storage keep filling up?
Because six things grow on their own and none of them shrink until space runs out. Each is a sensible default; together they add gigabytes a month.
| What grows | Roughly how fast | Can you stop it |
|---|---|---|
| Local Time Machine snapshots | Hourly, thinned when space is short | Only by turning off Time Machine |
| Application caches | Continuously, unbounded in many apps | Per app, if it has a limit setting |
| iCloud Drive and Photos downloads | Whenever you open a file or photo | Yes, with Optimize Mac Storage |
| Device backups | One full copy per backup | Yes, delete old ones after each new phone |
| Downloads and installers | Every time you install something | Yes, it is a habit rather than a setting |
| Developer output and package caches | Every build | Yes, but it comes back with the next build |
Why is my Mac storage still full after I delete files?
Because deleted files often have not left yet. They sit in the Trash until it is emptied; photos sit in Photos' Recently Deleted album for 30 days; and a file that was in a local snapshot keeps its space until that snapshot expires, which is why the free figure can stay put after a large delete. What purgeable space is explains the last one.
How do I find what is filling up my Mac?
Take one measurement now and another in a fortnight. Two listings a week apart tell you more than any amount of guessing:
du -xh -d 1 ~ 2>/dev/null | sort -h | tail -20 > ~/Desktop/space-$(date +%F).txtRun it again later and compare the two files. The folder that moved is the one to deal with, and it is often a hidden one. On our MacBook Air the two largest movers were ~/Library/Caches (9.1 GB, almost half of it Chrome) and the per user cache folder under /private/var/folders (3.0 GB).
Does iCloud fill up my Mac?
It can. With iCloud Drive or iCloud Photos on, every file and photo you open is downloaded to the Mac and stays there. Turning on Optimize Mac Storage in System Settings, your name, iCloud lets macOS remove local copies of older items when space runs low; they download again when you open them.
What should I do when my Mac storage is full?
- Empty the Trash, and Photos' Recently Deleted album.
- Turn on Empty Trash Automatically in System Settings, General, Storage. It is the one recommendation with no downside.
- Clear app caches in
~/Library/Caches, app by app, and set cache limits in the apps that offer them, such as Spotify and Telegram. - Delete the previous device backup when a new phone is set up.
- Clear Downloads after each install finishes.
The full sequence, from safest to most involved, is in how to free 100 GB, and temporary files have their own page: how to delete temp files on a Mac.
Common questions
Why does my Mac storage keep filling up?
Mostly local Time Machine snapshots, app caches that grow without limits, and iCloud files downloaded when opened. All three keep what they add until the disk runs short, so free space falls even when you save nothing new.
Why is my Mac storage full after deleting files?
Deleted files can still be in the Trash, in Photos' Recently Deleted album for 30 days, or held by a local snapshot until it expires. Empty both, then give macOS a little time to thin snapshots.
How can I tell what is filling up my Mac?
Save a folder by folder listing now and compare it with a second one in a fortnight. The folder that grew is the answer; on our MacBook Air it was ~/Library/Caches, at 9.1 GB.
Is my Mac filling up because of a virus?
Almost never. On a Mac, unexplained growth is nearly always snapshots, caches, iCloud downloads, device backups or downloads. Measure the folders before assuming anything else.