CleanWhat is "System Data" on Mac and how do you shrink it?
"System Data" is the bucket where macOS puts everything it can't categorize. It's not one file: it's caches, Time Machine snapshots, simulators, virtual machines, app leftovers and more. That's why it can hit 20, 60 or 100 GB.
What's usually inside
App and browser caches (safe to delete). Local Time Machine snapshots (macOS deletes them on its own when it needs space). Downloaded updates waiting to install (don't touch). Simulators, Docker and virtual machines if you code. Leftovers from uninstalled apps.
Local Time Machine snapshots
Regenerates, with a costIf you use Time Machine, your Mac keeps temporary copies on the internal drive. See how many there are with:
tmutil listlocalsnapshots /macOS removes them automatically when it needs space. You usually don't need to touch them.
Don't delete a half-installed update
Don't touchA downloaded macOS update can take almost 10 GB of "System Data". That space frees itself once you install it. Deleting it by hand can break the update: install it or wait.
What you can clean today
SafeCaches, leftovers from uninstalled apps and, if you code, simulators and developer caches. Those three are usually most of "System Data".
FAQ
Why doesn't "System Data" go down after I delete things?
macOS takes a while to recalculate it and sometimes only updates after a restart. And if what you deleted is still in the Trash, it still takes up space.
Does restarting help?
A little: restarting clears temporary files and applies any pending snapshot cleanup.
Keep reading
How to free up space on your Mac: the complete guide (2026)
Step by step to reclaim tens of GB on your Mac without deleting anything important: what to check first, what's safe, and what to never touch.
How to safely clear the cache on your Mac
What your Mac's cache is, how much space it takes and how to clear it without breaking anything. Steps for Finder and Terminal.
How to free up space from Xcode and iOS simulators
DerivedData, simulators, iOS runtimes and DeviceSupport can take 20–90 GB. What to delete and how to do it right.