Mac Slow After a macOS Update: What's Normal, What Isn't

For the first few days after a major macOS update, a slow, warm Mac is usually normal: Spotlight indexing, Photos analysis and iCloud sync run in the background. Leave it on power overnight; if it’s no better after a week, look for the cause.

You updated, and it feels like someone swapped your Mac: the fans are loud, the case is warm, the battery melts, windows open with a lag. The first thought is that the update broke everything. Usually it didn’t: for the first few days after a major update the Mac does a lot of background work, and you can feel it.

Below: what exactly it’s doing, how to help it finish, and where “just wait” ends.

What the Mac does after an update

A major update — say, to macOS 27, released on September 14, 2026 — is a new system, and a lot gets recalculated from scratch:

• Spotlight indexing. The Mac rescans your files so search can find them by content. Apple says that depending on how much data you have, this can take hours or even days, and it goes fastest when the Mac isn’t in use, is connected to power and is online over Wi-Fi or Ethernet. The index stays on the Mac.
• Photos library analysis. Photos re-examines your pictures and videos — people, objects, text — everything search relies on later.
• iCloud sync. Files, photos and notes download and reconcile.
• App and cache updates. Apps catch up with the new system, and the system rebuilds its own caches.

In Activity Monitor, on the CPU tab, this work shows up under its own names. On macOS 27 these are:

You’ll often see mediaanalysisd nearby too — a system media analysis service. Apple doesn’t document it, but it’s part of macOS as well.

They’re parts of the system, not malware, and there’s no need to quit them: they’d start again and begin from scratch. How to use Activity Monitor itself is covered in the guide to Activity Monitor.

How to help it finish

The best thing you can do is stay out of the way. Leave the Mac overnight:

1. plug in the power adapter;
2. don’t close the laptop lid — a closed Mac sleeps and the work stops;
3. don’t let it sleep on a timer — see how to keep your Mac awake;
4. leave Wi-Fi on.

In the morning, open Activity Monitor and check the CPU tab: if mds_stores and photoanalysisd are no longer near the top, the bulk of the work is done.

How long to wait

There’s no exact figure: Apple only says indexing can take hours or days, depending on how much data you have. A large Photos library or hundreds of gigabytes of files stretch it out. The main sign that all is well: the load drops noticeably from day to day.

Our rule of thumb is a week. Time to look for a cause if, after a week:

• the CPU is still busy with the same background processes even when the Mac is sitting idle;
• the Memory Pressure graph on the Memory tab is yellow or red most of the time — more in the guide on memory pressure;
• one particular app drags while everything else is fine.

If it doesn’t pass

1. Update all your apps. After a major macOS update, old app versions are a common cause of slowdowns — especially menu bar utilities, antivirus, VPNs and anything that installs system extensions. System Settings → General → Software Update for macOS itself; the App Store and developers’ sites for the rest.
2. Check what starts on its own. System Settings → General → Login Items & Extensions. Remove what doesn’t need to start every time, especially things you haven’t opened in ages.
3. Check disk space. System Settings → General → Storage. The update itself takes space, and with the disk nearly full macOS has no room for caches and swap.
4. Wait for the first fix. The first bug-fix releases arrive fast: macOS 27.0.1 came out two weeks after 27.0. If the slowdown looks like a system bug, it’s worth updating to it.
5. Try safe mode. It keeps some third-party software from loading at startup. On a Mac with Apple silicon: shut down, press and hold the power button until “Loading startup options” appears, select your disk, then hold Shift and click Continue in Safe Mode. Faster in safe mode? The culprit is among your login items or extensions.

After that comes the full step-by-step diagnosis: memory, CPU, disk, heat.

What not to do

• Don’t install cleaners or “boosters”. They won’t speed up indexing, and the memory they free fills right back up with cache.
• Don’t quit mds_stores or photoanalysisd. The system restarts them and the work begins again.
• Don’t reset the SMC. Macs with Apple silicon have no separate SMC reset — Apple says it resets itself when you restart.
• Don’t roll back in a hurry. The standard way back is restoring a Time Machine backup made before the update, and anything that changed since then is lost. Give the Mac those few days first.

In the app

Mac Resources lets you see whether the load is easing without opening Activity Monitor every time. The menu bar item shows whichever of CPU, memory or GPU is busiest and turns red above 80%. During indexing it may stay red for a long while because of the CPU — that’s expected.

The CPU widget and the large Last Hour widget draw a graph for the past hour. That shows what matters: whether the load comes in waves and eases, or stands like a flat wall. Widgets refresh once a minute — macOS doesn’t allow more often. The Disk widget shows how full the system volume is, like “2.4 of 4.0 TB” — that’s space, not disk activity.

There’s no process list in the app: the macOS sandbox doesn’t provide one. To see what exactly is loading the Mac, use Activity Monitor. And to leave the Mac overnight to finish indexing, its menu has Prevent sleep — details in how to keep your Mac awake.

If a week has passed and the Mac is still slow, move on to the step-by-step diagnosis.