High CPU usage on a Mac: what counts as high, and what to do

CPU use on a Mac counts as high when it stays high for minutes without you asking for anything. A burst to 80 or 100 percent while an app opens, a page loads or a file exports is normal and passes in seconds. A figure that stays well above idle with nothing running is the signal, and the fix is to find the one app behind it, then wait, quit it, slow it down or update it.

The rest of this post explains why the same number can mean different things, how to read it, and what each response does.

Why a high figure is not always a problem

The processor exists to be used. When an app needs it, it takes as much as it can for as long as the job lasts, then lets go. Exporting a video, compressing a folder, loading a heavy web page and installing an app all push the figure up. That is the Mac doing what you asked, quickly.

So the useful question is not how high the number is. It is whether the number matches what you are doing:

• High while you work on something heavy, falling when you stop. Normal.
• High for a few seconds after you open an app or wake the Mac. Normal. Apps do their set-up work and settle.
• High for many minutes while you are only reading or idle. Not normal. Something is stuck, or doing a long job in the background.
• High all the time, regardless of what you do. Look for a runaway app or a background process that never finishes.

A useful test is to leave the Mac alone for a minute with your apps as they are, then look. If the figure is still high, you have something to find.

Per-core and whole-Mac figures

CPU figures come in two forms, and mixing them up causes most of the confusion.

A whole-Mac figure is one number for everything: 25 percent means a quarter of all the processing capacity is in use. Foreman’s menu bar readout shows this kind of figure.

A per-core figure counts each core as its own 100 percent, so an app using two cores fully shows as 200 percent. Terminal’s top counts this way, which is why an app there can read well past 100. Both views are right. They count against different totals, so a single app at 150 percent on a many-core Mac may be only a part of the whole machine.

What this means in practice:

• Do not panic at a per-app figure above 100 percent. Check how many cores the Mac has first.
• Compare like with like. An app’s share against the whole-Mac total tells you whether it is the main cause.
• A Mac with a few busy cores and many idle ones can show a modest whole-Mac figure while one app is still stuck at full tilt on its own core.

In Foreman, each app’s CPU figure on the Processes page is a share of the whole Mac, with the Mac’s total above the column, so you can read an app against the whole at once. On the Performance page, the CPU graph can show Overall or Each Core, so you can see one core working flat out while the rest are idle. That page also lists user and system time, the number of processes and threads, how long the Mac has been up, and how many performance and efficiency cores the Mac has.

Find what is using it

Open Foreman with Control-Shift-Escape and go to Processes. Click the CPU column to sort the list, with the busiest at the top. Apps, Background processes and System processes each have their own section, and an app’s helper processes are added up under it, so a browser with twenty helpers shows as one row with its real total. Open the row to see which helper is the busy one.

Then watch for half a minute. The one that stays at the top is the problem, not the one that flashes past. If a process name is unfamiliar, Foreman shows a plain-English name for about 120 macOS processes with the real name beside it in grey. For a process Foreman does not know, the Search Online command on the right-click menu does a web search for its name.

The macOS Force Quit window (Option-Command-Escape) lists your open apps, which helps you spot an app you forgot was running, but it does not show any CPU figures.

What to do about it

Choose by what the process is.

It is doing a real job. Exporting, indexing, backing up. Let it finish. Check again in a few minutes. Why is my Mac slow after a macOS update? is the common case here.

It is an app you do not need. Quit it. Select it in Foreman and press End Task. This asks the app to quit the way Command-Q does, so it can offer to save your work. If it is still open, press End Task again within a minute to force quit it. If macOS has marked it “Not responding”, End Task force quits it at once.

It is an app you need open but not right now. Use Efficiency Mode. While the app is in the background it runs at background priority and in short bursts, held to about a quarter of the processor time it would otherwise take. In front, or while playing sound, it runs at full speed. Foreman remembers the choice for that app. How much it helps depends on how busy the Mac is; there is no fixed amount.

It is an app that was fine until recently. Update it. A new version often fixes a runaway loop, and a macOS update can leave an older app misbehaving until the app catches up. Check the App Store or the app’s own update option. If it is a browser, also close the tabs you do not need.

It is part of macOS. Do not end it. If it runs under your account, such as Media analysis or iCloud Drive, Efficiency Mode can slow it while you work. Many system processes are restarted by macOS on their own, and some, such as WindowServer and loginwindow, will log you out if ended. Foreman warns before ending those, and never offers to end kernel_task or launchd. If kernel_task is high, the Mac is probably slowing itself down to stay cool, and the answer is to find the app that made it warm. What is kernel_task on a Mac explains it.

When it keeps coming back

If the same app returns to the top every day:

1. Check for an update to the app.
2. Check its own settings for background syncing, auto-scanning or live preview options you can turn off.
3. Look at Startup Apps in Foreman, which lists everything that opens at login or runs in the background, grouped by the app it belongs to. A helper you did not know about may be the one working.
4. If none of this helps, the app is simply heavy for your Mac, and the options are to use it less or to use Efficiency Mode when it sits in the background.

A quick reference

• Spike, then calm: normal work. Do nothing.
• High for minutes while you are working: a real job. Wait.
• High while idle, in an app you know: stuck or syncing. Quit it, update it, or use Efficiency Mode.
• High in a system process: macOS doing upkeep. Wait, and do not end it.
• High while the Mac is hot: it may be slowing itself to cool. Find the app behind the heat.

Foreman is $12 once, covers up to 3 Macs, and is free for 24 hours, so you can sort your own Mac’s processes by CPU and see how a quiet one looks. Most of the answers above, though, come from one habit: leave the Mac alone for a minute, and see what is still busy.