How to Reduce System Data on Mac (Step-by-Step)
The right order of operations for actually shrinking that gray System Data bar, plus what to do when you have done all the obvious things and the number will not move.
By Ram Velmurugan · Founder & Lead Developer, 1dot.ai
You already know System Data is huge. That part is not the hard bit anymore, everyone finds their way to System Settings, General, Storage eventually and sees the gray bar with a number that makes no sense. The hard bit is what to actually do about it, in what order, without breaking anything or wasting an afternoon deleting things that turn out not to matter.
This is that order. If you have not read what System Data actually contains, our companion guide What Is System Data on Mac, and Why Is It So Big? covers that in depth. This one skips straight to the doing.
tmutil. That alone clears most of what makes System Data swing high. After that, clear app caches, remove old device backups and leftover macOS installers, and delete apps you have not opened in a year. A cleaner such as Files Magic AI can automate the caches, duplicates, and developer-artifact part in one pass.What Actually Gets Smaller
Not everything in System Data can shrink, and it helps to know that going in so you are not chasing zero. Three things account for almost all of the reclaimable space: local Time Machine snapshots, app and system caches, and leftover files from things you already deleted or updated, like macOS installers. Old iPhone and iPad backups are counted under the iOS Files category, not System Data, but they sit on the same drive, so step 6 covers them too.
What will not shrink, no matter what you do: the operating system files under /System and fonts and plug-ins. (Apple Intelligence's on-device models are reported under the macOS category, not System Data.) Those are small relative to the reclaimable categories, so leaving them alone costs you almost nothing.
Before You Start
Open Apple menu, System Settings, General, Storage and note the current System Data figure. On macOS Ventura through Tahoe this is where the storage bar lives; on older versions it is under Apple menu, About This Mac, Storage, Manage. Hover the bar to see each labeled category next to System Data.
One thing worth knowing before you touch anything: this number is an estimate that recalculates in the background, not a live figure. If you just ran a big file operation, an app update, or a Time Machine backup, it can read high for a while and settle on its own. If today's number looks unusually inflated compared to what you remember, give it a few minutes before starting.
The Step-By-Step Order
Work through these in order. The first three handle the biggest, most common causes. The rest mop up what is left. Most people never need to go past step 4 or 5.
Restart your Mac
Free · 2 minDo this first, always. A restart clears virtual memory swap files and the sleep image, and it prompts macOS to thin local snapshots in the background. If your Mac has been awake for weeks, this one step alone can drop System Data by several gigabytes with zero risk. Re-check the storage screen after it comes back up.
Empty the Trash, then wait
Free · 5 minEmpty the Trash, then leave the storage screen closed for a few minutes before checking again. Files you just deleted can still be held inside a local snapshot, so the space does not reappear the instant you empty it. This delay is the reason so many people think emptying the Trash "did nothing." It usually did something, it just has not shown up yet.
Thin or delete local Time Machine snapshots
Terminal · 5 minThis is the step that moves the biggest numbers. macOS keeps hourly local snapshots on your internal disk even when your Time Machine drive is not connected, and they can hold tens of gigabytes of recently changed files. Open Terminal and list them:
tmutil listlocalsnapshots /Each line is a dated snapshot. To remove one specifically, pass its date and time to:
sudo tmutil deletelocalsnapshots 2026-08-04-114500To free a target amount instead of picking snapshots one by one, use thinlocalsnapshots with a byte count and an urgency level from 1 to 4:
sudo tmutil thinlocalsnapshots / 10000000000 4That example asks macOS to try to free roughly 10 GB at the highest urgency. In practice, the simplest option is to just free a little space elsewhere and restart, since macOS thins snapshots automatically once the disk gets tight. Reach for these commands only when you need the space back right now.
Clear app caches
Manual · 10 minIn Finder press Command Shift G and go to ~/Library/Caches. Sort by size. Each folder is named after the app that made it. For apps you recognize, you can open the folder and delete what is inside, leaving the folder itself in place so the app can rebuild it. Do not delete folders you cannot identify.
Clean Mail and Messages attachments
Manual · 10 minMail and Messages have their own storage categories, separate from System Data, but a lot of people land on this guide because their overall storage is tight and these two are common hidden hogs. In Mail, select a message and choose Message, Remove Attachments to keep the email but drop the file. The cache copies Mail keeps locally live at:
~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads/That folder is safe to clear entirely, it holds copies, not the only version of anything. In Messages, open a conversation, scroll to the Photos and Files section in the details panel, and delete large attachments you do not need to keep. Deleting an attachment in Messages removes it immediately rather than sending it to the Trash, so only remove things you are sure about.
Delete old iPhone and iPad backups
Free · 3 minConnect the device, open it in Finder, and on the General tab click Manage Backups. Every local backup shows with its date. Delete the ones from devices you no longer own or dates you do not need. Apple files these under their own iOS Files storage category, not System Data, but they do not shrink on their own either way, so an old backup can sit there indefinitely until you remove it.
Remove leftover macOS installers
Free · 2 minCheck your Applications folder for anything named Install macOS followed by a version name. After you have updated, that installer is dead weight at 12 to 15 GB, and it is filed under System Data. Drag it to the Trash and empty it.
Review and remove apps you no longer use
Manual · 10 minmacOS does not auto-offload unused apps the way iOS and iPadOS can, so this one is manual. In System Settings, General, Storage, open the Applications category and sort by last used. Anything you have not opened in a year is a safe candidate. The app itself counts under Applications, but removing it also clears its cache, log, and support files in ~/Library, which do count as System Data.
Automate the cache, duplicate, and developer-cache cleanup
Files Magic AIBy this point you have handled snapshots, backups, installers, and the obvious caches by hand. What is usually still scattered around is duplicate files, developer build artifacts, and cache folders you did not think to check. That is the tedious, repetitive part worth automating, and where a dedicated cleaner earns its keep. More on exactly what it does and does not touch below.
Why It Is Still Huge After All That
If you have done the steps above and the number barely moved, one of these is almost always why.
You checked too soon
The storage bar recalculates in the background, and snapshot thinning in particular can take a while after a large deletion. Give it 15 to 20 minutes after a big change before deciding a step did not work.
Snapshots came back
If you did not delete your source files, thinning a snapshot does not stop macOS from creating new ones. Time Machine keeps an hourly local snapshot for roughly the last 24 hours, plus the last complete backup for any destination that has not connected in that window, so a backup drive you only plug in once a week can be the reason a chunk of snapshots never ages out. Snapshots are how Time Machine tracks recent changes, so they will always regenerate. The goal is not zero snapshots, it is not letting a large backlog build up.
tmutil fails with a "Stale NFS file handle" error
If sudo tmutil deletelocalsnapshots comes back with something like Failed to delete local snapshot '2025-11-17-031807' and a POSIX error 70 ("Stale NFS file handle"), stop retrying the same command. Mac users started reporting this exact failure on macOS 26.1, and in the cases we have seen reported, the fix was not in Terminal at all: open Disk Utility, select the Data volume, choose View > Show APFS Snapshots, select the stuck snapshot, and remove it with the minus button. Deleting through Disk Utility's GUI has succeeded for people in threads where the tmutil command kept throwing the NFS error. If the error keeps coming back and points at a network backup destination, the problem is usually the destination, not the Mac. A Time Machine backup to a NAS over AFP, for example, is no longer supported; reconnecting it over SMB with an ASCII-only share name has resolved that specific case.
The number in Disk Utility is not the sum of the list
Selecting every entry under View > Show APFS Snapshots and adding up each listed size overstates what you will actually get back. Click Calculate at the bottom of that panel instead and read the "private size" figure. Snapshots share unchanged data blocks with each other, so the space unique to any one snapshot, the part that is actually freed when you delete it, is usually well below the sum of the sizes shown next to each entry.
Finder and df are both right, just about different things
Run df -h / in Terminal and compare it with the storage bar in System Settings. The two numbers routinely disagree because the storage bar counts purgeable snapshot space as used, while df reports it as available, since macOS can reclaim that space the instant something else needs it. A gap between them is not a sign that either tool is broken. It means the space is spoken for but not yet deleted.
The reclaimable share was already small
Some Macs genuinely do not have much to give back. If snapshots are already thin, caches are already small, and there are no old backups or leftover installers, a 20 to 25 GB System Data figure is just normal. Chasing it lower than that is not worth the time.
The heavy hitter is developer or duplicate clutter, not the usual suspects
On an active developer Mac, node_modules folders and Xcode DerivedData can add 30 to 60 GB on their own, and macOS files most of that under System Data rather than Documents. We cover this specifically in the guides on cleaning Xcode cache and deleting node_modules across every project. If you write code, check these before anything else.
Something outside System Data is actually the problem
It is easy to blame System Data when the real issue is a bloated Photos library or a Documents folder full of large exports. Check the other labeled categories in the storage bar too. The full picture, beyond just System Data, is in our guide on how to free up disk space on Mac.
Shrink the caches hiding in System Data
Much of what System Data counts is cache and build output. System Cleaner finds node_modules, Xcode caches, Gradle caches and old installers, shows their sizes, and removes nothing on its own.
macOS 12 or later. 25 free AI renames, no account needed.
Which Step Frees the Most
| Method | Effort | Typical space freed | Risk |
|---|---|---|---|
| Restart | None | 1 to 10 GB | None |
| Empty Trash + wait | None | Varies | None |
| Thin local snapshots (tmutil) | Low, Terminal | 10 to 80 GB | Low, deletes only backup copies |
| Clear app caches by hand | Medium | 2 to 15 GB | Low, stick to apps you recognize |
| Mail / Messages attachments | Medium | 1 to 20 GB | Medium, Messages deletions are immediate |
| Delete old device backups | Low | 4 to 30 GB each | None, only if device no longer needed |
| Remove macOS installers | Low | 12 to 15 GB each | None, re-downloadable |
| Remove unused apps | Medium | Usually small | Low |
| Files Magic AI System Cleaner | Low | 10 to 40 GB | None, review-first, Trash first |
If you only have ten minutes, do steps 1 through 3. That trio covers the two biggest, most variable causes of a swollen System Data figure and costs nothing but time.
What Not to Touch
- Anything inside the top-level
/Systemfolder. It is the OS itself. - Folders in
~/Libraryyou cannot identify. If you do not recognize the app, do not touch it. - Apple Intelligence model files on supported Macs. They are doing active work.
- Fonts and system plug-ins. The space saved is small and the risk is not worth it.
Every step in this guide targets a specific, named category, not a blind sweep through System folders. That is the whole safety model: know exactly what you are removing before you remove it.
Where Files Magic AI Fits
Steps 1 through 8 are things you do yourself with built-in macOS tools, and together they handle the largest and most common causes of a bloated System Data figure. What tends to be left over is scattered: duplicate files you forgot about, developer caches buried in project folders, apps that quietly went unused, and old DMG installers from software you downloaded once. Finding all of that by hand means opening a lot of folders.
Files Magic AI's System Cleaner runs one scan and groups what it finds by category: Duplicate Files, Unused Apps, Developer Caches (node_modules, Xcode, Flutter, Gradle), and DMG installers, each with its size and path shown. Nothing deletes automatically. You review the list, uncheck anything you want to keep, and whatever you clean goes to the Trash first, not straight to permanent deletion.
To be direct about the boundary: it will not touch Time Machine snapshots and it will not touch system files, and it should not. Those are handled by steps 1 through 3 above. What it automates is the tedious cache, duplicate, and developer-artifact sweep, which for most people is the largest chunk of what is left after the manual steps.
Pricing is free to start, then $6.99 a month, $34.99 a year, or $49.99 once for lifetime access, with a 3 day free trial on both the monthly and yearly plans, and no credit card required to start.
Keeping It Down Long-Term
System Data will always grow back somewhat, because caches and snapshots are part of how macOS stays responsive. The goal is a stable, healthy range, not zero. A few habits keep it there without becoming a chore:
- Restart weekly. One minute, and it keeps swap and snapshots from stacking up unnoticed.
- Back up devices to iCloud instead of your Mac unless you have a specific reason for a local copy. Local backups never clean themselves.
- Delete the macOS installer the day after a successful update, not months later.
- Run a cache and duplicate scan quarterly. Developer caches rebuild fast, so a quarterly pass catches what daily use misses.
- Stop checking the number daily. A System Data figure in the 12 to 25 GB range is healthy. Once you are there, leave it alone.
For the wider view of where a full Mac loses space beyond System Data, the roundup of the best Mac disk cleaner apps in 2026 compares the tools that automate this end to end.
Frequently Asked Questions
tmutil listlocalsnapshots / to see how many you are carrying, and thin them directly if you need the space back now.~/Library/Caches, or developer folders like node_modules and Xcode DerivedData. Sort the Applications and Documents categories in System Settings, General, Storage by size to see what is actually large.tmutil command kept throwing the error. If it keeps recurring and points at a network backup destination, the fix is on that destination, for example reconnecting a NAS over SMB instead of the no-longer-supported AFP.~/Library, and those are counted as System Data. If you have not opened an app in a year, removing it is a safe, if usually small, win.External References
- Apple Support: Free up storage space on Mac
- Apple Support: Change Storage settings on Mac
- Apple Support: Find and delete files on your Mac
Clear what the Storage pane will not
macOS gives you no button for Xcode caches or duplicate files. System Cleaner lists both by size and leaves the deciding to you, and Magic Rename tidies the files you keep.
macOS 12 or later. 25 free AI renames, no account needed.
Published August 5, 2026 · More guides · Files Magic AI