Here's how to clear that Giant System Data number on your Mac

You open Storage settings one day, see "System Data" sitting there eating 166GB, and your stomach drops a little. What is it? Can you delete it? Why is it so big? And why does Google immediately try to sell you five different cleaner apps that all want your admin password?

System Data is not one folder you can march into and empty. It's a junk drawer. macOS shoves a bunch of stuff in there that doesn't fit neatly into Apps, Photos, Documents, or Music.

We're talking caches, logs, temporary files, Time Machine local snapshots, app support files, disk images, old archives, leftover iPhone backups, fonts, plug ins, and a pile of system resources. Some of it the Mac genuinely needs. Some of it is temporary and will clear on its own. And some of it you can absolutely tidy up using tools Apple already gave you.

So no, you don't need a third party app. You don't need Terminal. You definitely don't need one of those one click "purge" utilities. Let me walk you through how I do it.

A quick word before we start

Your goal is not to drive System Data to zero. That's not a thing, and chasing it will just make you crazy. macOS uses this storage dynamically, so the number goes up and down as the system breathes. What we're doing is clearing out the obvious clutter and giving the Mac some room. That's it.

Trust me on this one, the safe wins are also the big wins.

Step 1: Start where Apple already shows you the mess

Before you go spelunking into hidden folders, look at what macOS is already telling you.

Go to System Settings > General > Storage.

You'll get a color coded bar across the top and, below it, a list of Apple's own recommendations: store files in iCloud, optimize Apple TV downloads, empty the Trash automatically, and review large files. These are built right into macOS and they're designed to play nice with the system instead of fighting it.

The one I always click first is Review Large Files. Honestly, this is where the real storage hogs hide. Old installers, disk images, ZIP archives, exported videos, screen recordings, that duplicate project folder you forgot about. People blame System Data when the actual culprit is a 40GB video export sitting in their Downloads from last March.

Step 2: Take out the Downloads trash (literally)

Speaking of Downloads. This folder is where files go to be forgotten. Browser downloads, app installers, random PDFs, work files, image dumps, video exports. Months of it.

Open Finder > Downloads and sort by Size or Date Modified. Drag the obvious junk to the Trash.

Then, and this is the part people skip, actually empty it. Files in the Trash still take up space until you do.

Trash > Empty Trash.

Personally, I do a Downloads sweep about once a month. It takes two minutes and it's almost always the single biggest chunk of space I get back.

Step 3: Sort out Time Machine's local snapshots

This one surprises people. When your Time Machine backup drive isn't connected, your Mac quietly keeps local snapshots on the internal drive so you can still restore recent files. Apple manages these automatically and clears them as space gets tight, but if you haven't plugged in your backup disk in a while, they can pile up and inflate that System Data number.

The fix is almost annoyingly simple: connect your Time Machine drive and let a backup finish. Once it's done, macOS handles the snapshots far more gracefully.

You can check your setup under System Settings > General > Time Machine.

What you should not do is go digging into hidden folders to delete snapshots by hand. These are part of Apple's backup system, the Mac knows how to manage them, and manual removal tends to cause more problems than it solves. Plug in the drive, let it run, walk away.

Step 4: Let iCloud and Photos carry some of the weight

iCloud can genuinely shrink your local storage, as long as you use it on purpose.

Turn on Optimize Mac Storage under System Settings > Apple Account > iCloud. This keeps older files in iCloud and pulls them down when you need them. Great for anyone with a smaller SSD who already lives in iCloud Drive.

Look, I'm not saying this is for everyone. If you work offline a lot, or you're a video editor, designer, or developer who needs big project files available locally at all times, you'll probably want those on an external drive instead. Know your own workflow here.

Photos is the other big one. If you use iCloud Photos, flip on Optimize Mac Storage there too: Photos > Settings > iCloud > Optimize Mac Storage. It keeps lighter versions on the Mac and the full resolution originals in the cloud, so your library shrinks without you deleting a single picture.

And please, do not go poking around inside the Photos Library package in Finder. That thing is a database. Delete files in there and you can wreck your whole collection. Use the Photos settings, not Finder surgery.

Step 5: Clear out old device backups and app leftovers

Remember when you used to back up your iPhone to your Mac through Finder? Those backups might still be sitting on your drive, each one several gigabytes, long after you switched to iCloud Backup.

Plug in your iPhone or iPad, open it in Finder, and choose Manage Backups. Delete the old ones you don't need. I'd keep one recent backup around if you've got a big iOS update or a new phone coming, but ancient ones can go.

App leftovers are trickier. Video editors, audio apps, and design tools love to stash render files, sample content, audio instruments, and project caches. Instead of hunting through Library folders and guessing what's safe, open the app itself and use its built in cache or cleanup controls. Removing this stuff from inside the app is way safer than deleting random folders and hoping for the best.

Step 6: Restart (and use Safe Mode only if things get weird)

A simple restart lets macOS clear temporary files, finish background maintenance, and recalculate your storage. After a big cleanup, do it: Apple menu > Restart.

If the storage number seems stuck or your Mac is acting strange, Safe Mode can help, because macOS runs some checks and blocks certain software from loading at startup. The steps differ by Mac:

• Apple silicon: shut down, hold the power button until startup options appear, pick your startup disk, hold Shift, then choose Continue in Safe Mode.
• Intel based Macs: restart and hold Shift as it boots.

Then just restart normally. This isn't a daily thing, more of a "something's off" tool.

The stuff you should never touch

Here's my one real warning. The most dangerous mistake is seeing a big number and deleting files out of hidden system folders to make it smaller. Stay out of System, private, usr, bin, sbin, and the root level Library folders. Basically, if a location asks for your administrator password and you don't know exactly what's in there, leave it alone.

Same goes for cleaner apps that promise to nuke "junk" without showing you what they're removing. Some aren't terrible, but you don't need them, and a bad one will strip out caches, logs, and support files your apps expect to find.

And about caches, they're not the enemy. Your Mac and your apps use them to load faster and avoid re downloading things. Wipe them all and yes, System Data dips for a minute, but the apps just rebuild them and the number creeps right back, with your Mac feeling sluggish in the meantime.

My honest takeaway

Mac cleanup is a habit, not a one click purge. Start in Storage settings, clear out large files, empty the Trash, run a Time Machine backup, lean on iCloud and Photos optimization where it fits your life, ditch old device backups, and restart. Save Safe Mode for when things genuinely seem broken.

System Data is never going to disappear, and you don't want it to. The Mac needs that room. The whole trick is dead simple, clear out the stuff you know is yours before you ever go near the stuff that belongs to the system.

That's the routine. No risky tools, no admin password handed to a stranger, just a Mac with room to breathe.