Discrepancy in available HD space

[Just_Kevin]

I expect this to be a basic question, which is why I have it in Mac Basics. I'm still getting accustomed to MacOS.

I noticed earlier today Disk Utility was reporting ~135GB of free space on my MacBook with a 1TB HD. I have since removed what I expect to be well over 100GB, I was not really keeping track. This was accomplished mostly by offloading larger and older folders/files to an external drive. I also realized I had double-digit GB in the Trash, mostly from video editing projects, which I emptied.

Disk Utility is now reporting less free space (120GB), it even dropped a few GB after a reboot. Settings however, is reporting nearly 600GB free space. I had not checked Settings prior to now.

From some research, this seems to be tied to Time Machine backups? The OS is keeping those files in case I need them back, but they would get deleted if were to need the space. This is why Disk Utility is showing ~120GB free, but Settings is showing the nearly 600GB. I have Time Machine pointing to an external SSD, but the OS is still keeping those files locally as well. I think they are only kept ~24 hours though?

That's my theory at least. Am I correct?

 

[Bigwaff]

There is option in Disk Utility to show APFS snapshots. You can delete them if you wish, or let macOS do it when it decides to reclaim the space.

 

[NoBoMac]

Disk Utility graph does not include purgeable space. Click the info icon at upper-right of the window which will return a window that shows "purgeable + free" (aka the value in System Settings) and individual lines for "free" (what's showing in DU screen shot) and "purgeable".

OS will handle purging purgeable for wear leveling purposes:

Get detailed information about a disk in Disk Utility on Mac

Use Disk Utility to see detailed information about a disk or volume on your Mac.

support.apple.com

“purgeable space”—space that macOS can free up when needed by removing files from your computer (you can’t manually remove the files that are designated purgeable, but macOS removes them as space is required)