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Why your Mac is slow after a macOS update, and how to fix it

You install a macOS update, restart, and everything feels worse. Fans running, beachballs, apps launching slowly, battery draining faster than yesterday. This is extremely common and, in most cases, temporary. But there is a real distinction between the slowness that resolves itself in a day and the slowness that will still be there next week, and knowing which you have saves a lot of pointless troubleshooting.

Updated 2026-08-02 · Written by the CleanerMac team · macOS 13–15 tested

First, wait: the update is still working

A major macOS update kicks off several heavy background jobs that continue long after the progress bar disappears. Until they finish, your Mac is genuinely doing more work than usual, and no amount of cleaning will change that.

• Spotlight reindexing. Every file on the disk is re-catalogued. The process is mds and mds_stores, and on a large disk it can run for hours.
• Photos analysis. The photoanalysisd process re-runs face and scene recognition on your entire library. On a large library this can take days of intermittent work, though it pauses when you are on battery.
• Time Machine. The first backup after an update is often close to a full one.
• iCloud re-sync. Files and photos may re-download or re-verify.
• Dyld cache rebuilds and app re-signing. Apps that verify their signature on first launch after an update start noticeably slower exactly once.

Open Activity Monitor and sort by CPU. If mds_stores, photoanalysisd, backupd or bird are at the top, your Mac is not broken. Leave it plugged in and awake overnight and reassess in the morning. This single step resolves the majority of post-update slowness.

Check whether you actually have disk space

Updates need a lot of temporary room and leave debris behind. A Mac that was comfortable at 40 GB free before the update can be scraping along afterwards, and macOS becomes dramatically slower when free space runs low, because swap and cache writes have nowhere to go.

Check under Apple menu, System Settings, General, Storage. Aim for at least 15 to 20 percent of the drive free. If you are below that, this is your problem and nothing else on this page will matter until you fix it. Our guides to freeing up space and a full startup disk cover the fastest wins, and System Data storage explains the mysterious category that usually balloons after an update.

Audit login items and background agents

Updates frequently re-enable background items, and third-party utilities that were fine on the old version may now be misbehaving. Go to System Settings, General, Login Items and Extensions and look at both lists: Open at Login, and Allow in the Background. Turn off anything you do not recognise or do not need at startup.

Pay particular attention to older third-party software. Antivirus tools, VPN clients, backup agents, disk utilities and menu-bar apps install system extensions that hook deep into macOS, and an extension built for the previous OS version is a common cause of persistent post-update slowness. If one of yours has not been updated since before the OS release, check for a new version or disable it as a test.

Clear the caches the update made stale

Application and system caches built against the previous OS version are not always invalidated cleanly. Stale caches cause slow launches, odd rendering and repeated disk activity. Clearing them is safe because apps rebuild what they need.

• App caches in ~/Library/Caches, ideally with the relevant apps closed.
• Quick Look thumbnails, with qlmanage -r cache, if previews look wrong.
• Font caches, with atsutil databases -remove followed by a logout, if text renders strangely.
• Finder and Dock, with killall Finder and killall Dock, for UI glitches.
• DNS, with sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder, if network lookups got slow. See the DNS guide for detail.

CleanerMac exposes all of these as buttons in its Tune-Up tab and skips the caches of any app that is currently open, which is the one manual mistake that can cost you unsaved work.

Force a clean Spotlight reindex if search is broken

Sometimes the post-update index does not complete correctly and mds_stores stays pinned at high CPU indefinitely, or Spotlight returns nothing. The fix is to throw the index away and start over:

sudo mdutil -E /

Expect heavy CPU use for a while afterwards as it rebuilds, so run it when you can leave the Mac alone. You can also add folders temporarily to System Settings, Siri and Spotlight, Spotlight Privacy, and remove them again, which achieves the same thing through the interface.

The hardware reality nobody enjoys

There is one honest caveat. If your Mac is several years old and has just moved to a new major macOS version, some of the slowdown may be permanent. Newer releases assume more RAM and a faster SSD, and features such as Stage Manager, live wallpapers and on-device intelligence are not free. On a Mac with 8 GB of RAM, a new OS version genuinely leaves less headroom than the one before.

You can mitigate this: reduce transparency and motion in System Settings, Accessibility, Display; use a static desktop picture; keep fewer browser tabs open; and be strict about background agents. Our guides to freeing up RAM and speeding up a slow Mac go into the specifics. But no software tool can add memory, and it is better to know that than to keep chasing a fix that does not exist.

A sensible order of operations

1. Wait 24 hours, plugged in, and check Activity Monitor before doing anything else.
2. Confirm you have at least 15 percent free disk space, and free some if not.
3. Prune login items and background extensions, especially older third-party ones.
4. Clear stale app caches and restart Finder and the Dock.
5. Rebuild the Spotlight index only if search is actually broken.
6. Restart properly, using Restart rather than closing the lid, so caches are rebuilt cleanly.
7. Check for a point release. Apple ships fixes for early performance regressions within weeks.

Working through that list resolves the overwhelming majority of post-update complaints. Steps two, four and five are also just good routine, which is why they appear in our maintenance checklist. If you would rather not do them by hand, CleanerMac bundles the disk audit, cache clearing and tune-up actions into a single pass.

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