Why your Mac has less space after a macOS update

An update finishes, you check Storage, and there is markedly less free space than before. This is normal, it is mostly temporary, and there are two parts of it worth clearing by hand.

What the update left behind

The installer itself. A full macOS installer is 12 GB or more. Point updates download less, but “less” is still gigabytes. Usually it is removed automatically after a successful install, and sometimes it is not.

ls -lh /Applications/Install\ macOS*.app 2>/dev/null
du -sh ~/Library/Updates 2>/dev/null

If an Install macOS ….app is sitting in Applications and you have already updated, drag it to the Trash.

A pre-update snapshot. macOS takes an APFS snapshot before a major update so it can roll back if something goes wrong. Sensible, and it holds every file the update changed.

tmutil listlocalsnapshots /

These expire on their own, generally within 24 hours to a few days. If you are short now:

sudo tmutil thinlocalsnapshots / 30000000000 4

Give it a day or two after a major update before doing this, in case you need to roll back.

Rebuilt caches. Spotlight reindexes, dyld rebuilds its shared cache, apps recompile shaders. Several gigabytes appear across a few days, and that space is not coming back — it is the new normal for the OS you now run.

The system volume grew. Each macOS version is larger than the last. On a 256 GB machine, this is a permanent loss of a few gigabytes per major version and nothing can be done about it.

What to check first

df -h /System/Volumes/Data

Compare it with Storage settings. Right after an update the two disagree more than usual, because the pre-update snapshot is large and fresh: df counts it as used, Storage settings counts it as free because it can drop it. A good part of the apparent loss is purgeable and will vanish on its own.

The one that catches people

Spotlight reindexing after an update makes the Mac feel slow and the fans run, for anything from twenty minutes to several hours depending on disk size. It is not a fault and it is not something to fix. Check whether it is still going:

mdutil -s /

If indexing is in progress, wait it out before concluding the update made your Mac slow.

When the space genuinely does not return

Give it three or four days of normal use. If free space is still well down and tmutil listlocalsnapshots / shows nothing large, the space is being used by something real, and the update is a coincidence rather than a cause. The System Data article walks through where to look.

One specific thing worth ruling out: if the update failed partway and retried, an installer may have been downloaded twice.

find / -name "Install macOS*" -maxdepth 3 2>/dev/null

Before the next update

Two habits make this painless.

Leave 30 GB free before starting. Major updates want room to expand, and an update that runs out of space midway is a much worse afternoon than clearing space beforehand.

Do a clear-out first, not after. Empty Downloads and the Trash, thin snapshots, and start the update with headroom. It also makes the after-and-before comparison meaningful, so you know whether the update really took the space or you simply had less than you thought.