Every autumn Apple releases a major macOS update, and every autumn a wave of people search "Mac slow after update" wondering if they've done something wrong. The honest answer: you haven't. The slowness is real, but it has a straightforward cause, a predictable timeline, and a clear point at which you should start investigating more seriously.
This post explains what's actually happening, what to watch for, and what to do if things don't improve after a few days.
What does macOS do during an update?
The update installer itself is only the first part. When you restart into the new version of macOS, the operating system triggers a set of background maintenance jobs that can take hours, sometimes most of a day.
The main ones are:
Spotlight reindexing. Spotlight is the search tool built into your Mac (the magnifying glass in the top-right corner, or Command-Space). It keeps a database of every file on your drive so searches are instant. After a major update, that database often needs to be rebuilt from scratch because the new OS may organise or label files differently. On a Mac with a large drive or many files, this can run for four to six hours.
Photos library rebuild. If you use the Photos app, it checks and reorganises its library database to match any changes in the new OS. If you have thousands of photos or videos, this is not fast.
iCloud re-sync. macOS re-establishes its iCloud connection after an update and often re-verifies which files are local and which are stored in the cloud. You may see iCloud Drive and Desktop files re-downloading.
System Settings cache rebuild. Preference files and system caches that were valid on the old OS version get rebuilt to match the new one. This happens quietly and finishes quickly, but it adds to the background noise in the first few hours.
All of this happens while you're trying to use your Mac. Your processor and storage are split between your work and the system's housekeeping, which is where the sluggishness comes from.
The 72-hour rule
Give it three days.
This is the honest, consistent piece of advice from people who support Macs professionally: after a major macOS update, wait 24-72 hours before drawing any conclusions about whether your Mac is "slower now." Most of the background tasks finish within that window, and most Macs return to their normal speed on their own.
To help things along: leave your Mac plugged in and switched on overnight for at least the first two nights after an update. Low-Power Mode or a short sleep timer can interrupt the indexing jobs mid-run, which makes them take longer overall. Give the system the overnight hours to work uninterrupted.
If your Mac is back to normal after 72 hours, you're done. Nothing to fix, nothing to worry about.
Why might slowness persist after 72 hours?
If your Mac is still meaningfully slower after three days of normal use, the update itself probably isn't the cause anymore. Something else has surfaced. The most common culprits:
WindowServer memory leaks. WindowServer is the macOS process that draws everything you see on screen: windows, animations, the menu bar, transparency effects. Some macOS versions (including Sequoia and the early builds of Tahoe) ship with bugs that cause WindowServer to slowly consume more and more memory over hours or days without releasing it. If your Mac gets progressively slower the longer it's been since your last restart, this is worth checking. Open Activity Monitor (Command-Space, type "Activity Monitor"), click the Memory tab, and look for WindowServer. If it's using more than 2-3 GB of memory, restarting will fix it temporarily. For more on what WindowServer does, see this explainer on WindowServer.
Apple Intelligence background processing. If your Mac recently became eligible for Apple Intelligence (Apple's on-device AI features, available on M1 and newer), the first weeks after enabling it involve substantial background work as models download and initialise. This can feel a lot like general slowness. It settles down once the initial setup completes.
Incompatible apps. When a new macOS version changes internal APIs (the interfaces that apps use to talk to the operating system), older apps that haven't been updated can behave erratically, crash repeatedly, or use far more CPU than they should trying to work around the changes. If you notice one particular app is unusually slow or is causing your whole Mac to slow down, check whether the developer has released an update for the new OS.
Login items from old apps. macOS updates sometimes cause the background helpers that apps install (small processes that start automatically when you log in) to get confused about their new environment. They sit in the background consuming resources without doing anything useful. Open System Settings › General › Login Items & Extensions and look for anything you don't recognise or no longer use.
For a broader look at why Macs slow down over time beyond updates, the general slow Mac guide covers all the common causes in plain English.
Older Macs feel every update harder
A Mac from 2017 running macOS Ventura was already working harder than it was designed to. Add another update to Sequoia or Tahoe and the gap between what the hardware can do and what the software expects gets wider.
This isn't Apple being malicious. New OS versions are built and tested primarily on current hardware. The minimum supported specs usually include older machines, but "supported" and "fast" aren't the same thing. If your Mac is five or more years old, especially if it has an Intel chip rather than Apple Silicon (the M-series chips), each major update will feel a little heavier than the last. The background jobs take longer, and there's less headroom for your normal work while they run.
That said, even on older hardware, the 72-hour rule still applies. Things should settle. If a 2019 MacBook Pro was running fine before the update, it should return to that same baseline once the post-update housekeeping is done. Slower than a new Mac, but not slower than it was before the update.
What if it's still slow after a week?
At that point, stop waiting and start investigating.
Open Activity Monitor and look at two things: the CPU tab (sorted by % CPU, descending) and the Memory tab (look at the Memory Pressure graph at the bottom). If the memory pressure bar is regularly yellow or red, you have a memory problem worth addressing. See what memory pressure means for a plain-English walkthrough of what the graph is telling you.
Sort the Memory tab by the Memory column. Whatever process is at the top is your biggest consumer. If it's a browser, Slack, or a creative app, that's normal and you can manage it by closing unused tabs and apps. If it's a system process like kernel_task or WindowServer using an unusually large amount, that's a sign of a specific bug in the OS or a driver, and restarting is the fastest fix.
Apple publishes a knowledge base article on what to do if your Mac is running slowly that covers several of the same steps in official terms, if you want Apple's own guidance alongside this.
If you're on macOS Tahoe specifically and things still feel off, the post on macOS Tahoe slowness covers what's known about that release in more detail.
Should I downgrade?
Almost certainly not, and modern macOS makes it genuinely difficult.
Downgrading to a previous version of macOS is not like uninstalling an app. It requires booting into macOS Recovery, erasing your drive, and reinstalling the old OS from scratch, which means losing everything that isn't backed up. Apple also stops signing old macOS versions after a while, which can make installation impossible depending on your Mac and the version you're trying to return to.
The only situation where downgrading is clearly worth it is if your Mac has become genuinely unusable on the new OS, the problems persist after two weeks, and you need that Mac to work right now. Even then, it's a significant undertaking. The better path in almost every case is to wait, diagnose, and fix the specific cause.
One related point: if your Mac is your primary work tool, try not to update on the day a major macOS version releases. The first release, known as x.0, is where most of the bugs live. Waiting for x.0.1 or x.1 (which usually arrives within four to eight weeks) means those early-adopter bugs are already fixed before you install anything.