What Is System Data on Mac? How to Clear It
If you have opened Apple menu > System Settings > General > Storage and wondered what “System Data” actually is, you are not alone. It is one of the least self-explanatory categories macOS shows you, and it can look alarmingly large.
System Data is a catch-all bucket for files macOS itself manages: caches, log files, temporary files, fonts, app support files, plug-ins, Quick Look thumbnail caches, and often local Time Machine (APFS) snapshots. If you do software development, Xcode and other developer tool caches can also land here.
The important thing to set expectations correctly: this category is managed by macOS and its size varies depending on the current state of your Mac. It can never reach zero, and Apple does not publish a fixed “healthy” number of gigabytes it should stay under. If you see it at 40, 60, or even 100 GB, that is worth investigating, but there is no single baseline to compare against.
Diagnose before you delete
Before changing anything, find out what is actually contributing to the total. Go to Apple menu > System Settings > General > Storage. macOS breaks down space by category (Documents, Apps, Photos, and so on), and System Data sits alongside them. On older Macs running versions before macOS Ventura, the equivalent screen was under About This Mac > Storage, and the same catch-all category used to be called “Other storage,” a name Apple retired starting with macOS Monterey.
Storage recommendations here point you toward general cleanup (see Apple’s guide to freeing up storage space on Mac), but for System Data specifically, checking a few known culprits directly tends to be faster than waiting on the built-in suggestions.
Fixes, roughly in order of space recovered
Local Time Machine snapshots. If Time Machine is enabled, macOS keeps local APFS snapshots on your internal drive so you can restore recent versions even without your backup disk connected. These can grow large on a Mac with limited free space. You can list them with tmutil listlocalsnapshots / in Terminal, and macOS normally thins them automatically as space gets tight. If you want to stop automatic local snapshots altogether, do it through System Settings > Time Machine options rather than a Terminal command, since the old disablelocal flag no longer works reliably. I cover the exact steps in how to disable local Time Machine backups on Mac.
Trash and Downloads. Emptying the Trash and clearing your Downloads folder are two of Apple’s own recommended space-recovery steps, and they are the lowest-risk place to start. If you want this handled automatically going forward, see how to empty Trash automatically on Mac.
Developer tool caches. If you use Xcode, the ~/Library/Developer/Xcode/DerivedData folder holds build artifacts and generated files, not your project’s original source code, and Xcode regenerates them on the next build. Deleting it is common practice among developers when storage runs low. Simulator caches under ~/Library/Developer/CoreSimulator can also be worth checking.
Rebuild the Spotlight index. A corrupted or bloated Spotlight index can occasionally inflate System Data. Apple’s official fix is to go to System Settings > Spotlight > Search Privacy, add your disk to the excluded list, wait a moment, then remove it again to trigger a clean reindex. Full steps are in Apple’s guide to rebuilding the Spotlight index.
A restart is worth trying too, and it is usually harmless as long as you save any open work first, but I would not count on it to meaningfully shrink the System Data number itself.
When System Data is genuinely huge
If System Data looks unusually large for your Mac, say roughly 100 GB or more on a typical drive, that is worth digging into, and it usually points to something specific: an unusually large snapshot backlog, years of accumulated developer caches, or a misbehaving app dumping logs. Work through the list above in order, and check freeing up storage space on Mac for the broader cleanup checklist, including offloading files with iCloud Desktop and Documents, which can free up local storage space.
