Mac Slow After a macOS Update? Here's Why

Almost every macOS update is followed by a wave of “my Mac is slow now” posts, and most of them resolve themselves within two days without anyone doing anything. That's not a coincidence and it isn't imagination — there is a specific, finite list of jobs macOS runs after an update, and they are genuinely expensive. Here's what's running, how long it should take, and how to tell when it's stopped being normal.

What macOS is doing after an update

Open Activity Monitor, sort the CPU tab by % CPU, and you'll usually see the culprits by name:

• mds, mds_stores, mdworker_shared — Spotlight rebuilding its search index. This is the big one. On a full drive it can run for many hours.
• photoanalysisd — Photos re-scanning your library for faces, places and Memories. It only runs when the Mac is idle and on power, which is why it seems to never finish if you close the lid every evening.
• backupd — Time Machine. The first backup after a major update is unusually large because so many system files changed.
• bird, cloudd — iCloud reconciling its file state.
• syspolicyd — re-verifying apps the first time you open each one.

How to read Activity Monitor properly covers what each column is telling you.

How long “normal” lasts

As a rule of thumb: 24 to 48 hours of ordinary use. The single best thing you can do is leave the Mac plugged in, awake and logged in overnight — several of these tasks are deliberately deferred until the machine is idle and on power, so a Mac that gets shut every evening can stretch a two-day job across two weeks.

You can check on the biggest job directly:

# Is Spotlight indexing enabled and how far along? (read-only)
mdutil -s /

Give it room to work

An update consumes disk space — the installer, the new system volume, and a snapshot of the old one. If you were already short on space, you may now be well below the 10–15% free that macOS wants, and everything above will run slowly and stay slow. Check System Settings → General → Storage first; what to clear first and clearing local snapshots both apply.

When it's a genuinely heavier system

Sometimes the Mac is slower afterwards and stays that way, because the new macOS asks more of hardware that was already at its limit. This is most common on the oldest Mac still supported by a given release. It's not a fault, and there's no fix that undoes it — but you can claw back most of the difference by cutting visual overhead:

• System Settings → Accessibility → Display → Reduce motion — removes the animated transitions between spaces and full-screen apps.
• Reduce transparency in the same panel — replaces blurred backgrounds with solid colour, which measurably lowers WindowServer load. See the full guide.
• Disable window animations and speed up Mission Control.

The old-MacBook guide goes further into what's worth doing on ageing hardware.

If it hasn't settled after a few days

1. Restart. Not a joke — updates leave processes in odd states, and a restart resolves a surprising share of post-update complaints.
2. Check for a follow-up update. Apple ships point releases quickly after a major version for exactly this reason. System Settings → General → Software Update, or from Terminal with the softwareupdate command.
3. Update your apps. Third-party software that hasn't caught up with the new macOS is a common cause of persistent slowness and crashes. Check the App Store's Updates tab and each app's own updater.
4. Look for incompatible background software. In System Settings → General → Login Items, scan Allow in the Background for anything old — VPN clients, disk utilities and antivirus from before the update are the usual suspects.
5. Test in Safe Mode. On Apple silicon, shut down, hold the power button until Loading startup options appears, select your disk, hold Shift and click Continue in Safe Mode. On Intel, restart holding Shift. If the Mac is fast in Safe Mode, something you installed is responsible — more on Safe Mode.
6. Rebuild the Spotlight index. If mds_stores is still pinned days later, the index is stuck rather than working — rebuild it.

What not to do

Don't reinstall macOS as a first move; it's hours of work and rarely the answer. Don't turn off Spotlight indexing to stop the CPU usage — you'll break search to save a job that was about to finish. And don't install a cleaner app to “fix” a post-update slowdown; the tasks causing it are the ones you want to complete, not interrupt. There's more on that in are Mac cleaner apps worth it.

The settings-level fixes above are one-click, reversible toggles in Mainspring — labelled in plain English, with an undo button for every one.

Common questions

How long is a Mac slow after a macOS update?

Usually 24 to 48 hours of ordinary use while Spotlight reindexes and Photos re-analyses your library. Leaving the Mac plugged in, awake and logged in overnight lets the deferred tasks finish much faster.

Why is my Mac hot and loud after updating macOS?

The same background indexing tasks that slow it down also load the CPU, which produces heat and fan noise. It should stop within a day or two; if it does not, check Activity Monitor for which process is still running.

Should I reinstall macOS if my Mac is slow after an update?

Not as a first step. Restart, install any point update, update your apps, and test in Safe Mode first. Reinstalling takes hours and rarely addresses the actual cause.

Can I downgrade macOS if the new version is slower?

It is possible but involves erasing the disk and restoring from a backup made on the older version, so it is a significant undertaking. Try reducing motion and transparency first, which recovers most of the difference on older hardware.

Is it safe to turn off Spotlight indexing to speed things up?

It stops the CPU usage but breaks Spotlight search, Mail search and anything else built on the index. Since indexing is a finite job, waiting it out is almost always the better trade.