The macOS update finished and now your disk is fuller than before

You cleared space for the update, it installed successfully, and now there is less free space than there was before. This is normal, it happens with most major macOS releases, and the causes are consistent enough to check in a fixed order.

1. Pre-update snapshots

Before installing, macOS takes a snapshot so it has somewhere to fall back to if the install fails. Those snapshots stay until they expire, and each one can reference tens of gigabytes of changed data.

tmutil listlocalsnapshots /

Snapshots dated before the update are candidates for removal once you have confirmed the machine is stable and you have an external Time Machine backup.

sudo tmutil deletelocalsnapshots 2026-07-26-084512

2. Leftover installer files

ls -lh /Library/Updates/
du -sh /Library/Updates/* 2>/dev/null

Folders with numeric names are usually remnants of a completed update. Give it a few days of stable running before removing them, and move them to the Trash rather than deleting directly, in case something needs to roll back.

Also check for a downloaded installer sitting in Applications or your Downloads folder. A full macOS installer weighs 12GB to 15GB, and it is easy to forget it is there.

3. Spotlight rebuilding its index

After a major update, Spotlight re-indexes everything, which builds a temporary index that can occupy several gigabytes and makes the machine feel slow for a day or two.

mdutil -s /

If it reports indexing in progress, there is nothing to fix. Wait for it to finish, then recheck free space. Deleting the index to force a rebuild makes the situation worse, not better.

4. The system volume grew

Each macOS release ships slightly larger. The read only system volume goes from around 12GB to 16GB depending on version and hardware. That space is not recoverable, and it is not a problem to solve. It is worth knowing so you do not spend an afternoon hunting for it.

df -h / /System/Volumes/Data

5. Caches regenerated at the same time

An update triggers a wave of cache rebuilding: application caches, thumbnail caches, Photos library processing and browser site data. Most of it settles, but on a machine that was already close to full, the temporary spike is what pushes it over the edge.

du -sh ~/Library/Caches 2>/dev/null
du -sh ~/Library/Caches/* 2>/dev/null | sort -hr | head -10

Clearing the largest entries is safe and usually recovers the spike immediately.

If you are still short on space

1. Clear application caches, biggest entry first.
2. Remove pre-update snapshots once backups are confirmed.
3. Check for the installer file and old update folders.
4. Handle developer caches if you build software, since those grow independently of updates.
5. Search for large files you forgot about rather than guessing.

find ~ -type f -size +2G 2>/dev/null | head -20

How much free space an update really needs

Apple does not publish a number, and the range surprises people. As a working rule:

• A major upgrade, for example macOS 14 to macOS 15, wants roughly 30GB to 45GB free. The installer is 12GB to 15GB, and the installation itself needs room to build a new system snapshot alongside the old one.
• A minor update, like 15.3 to 15.4, is far lighter, usually 8GB to 12GB.
• A security response is usually under 2GB.

If the update fails or will not start, free space is the first thing to check, not the last.

Freeing space quickly, in the order that works

1. Empty the Trash. Obvious, and it is still the fastest single win.
2. Thin local snapshots. tmutil listlocalsnapshots / then tmutil thinlocalsnapshots / 1000000000000 4. Often returns 10GB to 60GB in under a minute.
3. Remove leftover installers. du -sh /Library/Updates/*, and delete only entries from versions already installed.
4. Clear developer caches. Xcode DerivedData alone regularly returns 20GB to 80GB, and it is regenerable output.
5. Remove the Docker disk image if you can rebuild it, which on a development Mac is usually the largest single item on the list.
6. Delete the big media. Old screen recordings and video exports are the largest files on most machines. Sort a treemap by size and you will find them in seconds.

Cleaning up after the update

Once the Mac has restarted successfully, most of the space comes back on its own. Two items do not:

du -sh /Library/Updates 2>/dev/null
du -sh ~/Library/Caches/com.apple.SoftwareUpdate 2>/dev/null

If either holds several gigabytes from a version you have already installed, it is safe to remove. Leave anything that matches the version reported by sw_vers alone, since that may be part of a pending installation.

Preventing the next one from being a problem

Keep free space above 15 percent of the drive rather than scrambling when a dialog appears. On a 512GB Mac that is about 75GB, which sounds like a lot until you count what Xcode and Docker will take by themselves. A monthly check of df -h / takes five seconds and removes the whole category of update failures caused by a full disk.

macoptimize tracks free space continuously and shows the trend rather than a single reading, which is how you notice that a machine is losing a gigabyte a week before it becomes urgent.

FAQ

Should I disable local snapshots permanently?

No. They are what make a Time Machine restore useful between backups, and they hold deleted files for a day. Thinning them when free space is tight is reasonable, disabling them permanently trades a real safety net for a number in the Storage panel.

Is it safe to delete /Library/Updates contents?

Only the leftovers from versions you have already installed. Check sw_vers first, then delete folders that belong to an older version. Removing the files for a pending update can cancel or corrupt that update, which is a worse problem than the disk space.

How long until the disk usage settles after an update?

Usually one to two weeks. Spotlight reindexes, Photos rebuilds previews, and system caches fill in over that period. If the number is still unexpectedly large three weeks later, run the audit in this guide and look for leftover installers or a developer cache.

Can I install the update if I am short on space?

Sometimes, but the install can fail partway and leave the Mac in a state that needs recovery. Freeing 20GB to 40GB first is faster than recovering from a failed upgrade, and the steps in this guide usually get you there in under ten minutes.

Does deleting files during an update cause problems?

Do not delete anything while the update is downloading or installing. The system is writing to snapshots and staging areas at that point, and removing the wrong file there can invalidate the whole update. Clean before you start or after it finishes, never during.