You installed a macOS update, your apps and files are exactly where you left them, and yet the free space on your Mac has dropped by 10, 20 or even 40 GB. Nothing you did explains it.

Most of that space isn’t lost. It is being used by things the update created, some of which clean themselves up and some of which you can remove. Here’s where it usually goes and how to get it back, starting with what’s safe.

Wait a day before you measure

In the first day or two after an update, the numbers are at their worst and least reliable:

  • Spotlight rebuilds its index, and Photos and Mail re-analyse your libraries. That temporarily uses extra space.
  • Storage settings take time to calculate. Categories may show as Calculating or lump everything into System Data until the scan finishes.
  • Some space is purgeable. macOS counts caches and snapshots it can remove automatically as used space in some places and as available in others.

If you aren’t actually running out of space, leave the Mac plugged in overnight and check again tomorrow.

Measure it properly

Different parts of macOS count free space differently, which is why the numbers disagree. For the most honest figure, open Terminal and run:

df -h /System/Volumes/Data

The Avail column is space you can use right now, without counting purgeable space. Finder’s Get Info on Macintosh HD usually shows a larger number because it includes space macOS can free up on demand.

Local Time Machine snapshots

If you use Time Machine, macOS keeps local snapshots on your internal drive, and it typically takes one before installing an update. They can hold a lot of space, especially if you deleted or changed large files since the snapshot was taken. To see them:

tmutil listlocalsnapshots /

macOS deletes these automatically after about a day, or sooner when space runs low, so usually you can simply wait. If you need the space now, delete a specific snapshot by its date:

sudo tmutil deletelocalsnapshots 2026-09-28-101500

Replace the date with one from your list. You lose only the ability to restore to that moment from the local snapshot; your Time Machine backups on the external drive are unaffected.

You may also see a snapshot named com.apple.os.update-… in Disk Utility. That is the sealed snapshot the system runs from. Leave it alone; it isn’t wasted space.

Leftover installers

If you downloaded a full installer, such as Install macOS Golden Gate, it may still be in your Applications folder. It is typically 15 GB or more. If the update has finished and you don’t need the installer to make a bootable USB drive, drag it to the Trash and empty it.

A failed or interrupted update can also leave a large staging folder behind. Check the size with:

sudo du -sh /Library/Updates "/macOS Install Data" 2>/dev/null

If either is large and your update completed successfully, restart once more; macOS usually clears these on the next boot. Don’t delete them while an update is pending in Software Update.

Apple Intelligence and new features

Major updates can download new on-device models and assets. Apple Intelligence alone can take well over 10 GB, and it can reappear after an update even if you had it off. Our guide to Apple Intelligence storage explains how much it uses and what you can actually do about it.

When it’s all in System Data

If Storage settings show a huge System Data category, that is a catch-all for caches, logs, snapshots, virtual memory files and app data macOS can’t categorise. It often shrinks by itself over a few days after an update. If it doesn’t, our System Data guide shows how to find what’s actually inside it.

What not to do

  • Don’t delete folders in /System or /private/var by hand. Some of them are needed to start the Mac.
  • Be careful with cleaning apps. Many simply delete caches that macOS rebuilds a day later, and some trigger exactly the indexing that uses more space.
  • Don’t delete the sealed system snapshot or try to disable System Integrity Protection to reclaim space.

The short version

Space that disappears after a macOS update is usually temporary: a pre-update Time Machine snapshot, index rebuilding, a leftover installer or new system assets. Wait a day, measure with df -h, delete old local snapshots and leftover installers if you need the space now, and look at Apple Intelligence and System Data if the gap is still large.