kernel_task High CPU on a Mac: What It Is and What to Do

kernel_task is the macOS kernel. When the processor gets too hot, it takes CPU time away from heavy apps, so its percentage in Activity Monitor climbs. It’s a symptom of heat, not the cause: find what heated the Mac, let it cool, and kernel_task settles down by itself.

Don’t try to quit kernel_task — look for whatever heated the processor.

What kernel_task is

kernel_task is the macOS kernel itself, not an app you can close. Every Mac has it, and it’s always in Activity Monitor’s list. Normally it uses only a few percent of the CPU: the kernel hands out processor time and memory and talks to devices.

One of its jobs, according to Apple, is to help manage CPU temperature. When the processor is too hot, kernel_task takes some of its time so that intensive apps can’t heat it further. In Activity Monitor this shows up as a high percentage for kernel_task, often together with fan noise. Apple stresses that kernel_task doesn’t cause the heat itself, and it reduces its activity automatically once the CPU cools down.

What it looks like

• In Activity Monitor’s CPU tab, kernel_task has climbed to the top with hundreds of percent. Percentages are counted per core and added up, so more than 100% on a multi-core Mac isn’t an error;
• apps stutter, exports get slower;
• the case is hot and the fans are loud. A MacBook Air with Apple silicon has no fan — it simply slows down.

What to do, step by step

1. Find what’s heating it. Open Activity Monitor (⌘-Space, type “activity”, Return), go to the CPU tab and sort by % CPU. Look at the rows below kernel_task: a browser with a heavy tab, a video export, a game, a code build. View → Windowed Processes leaves only your apps. How to read the tab is in the Activity Monitor guide.
2. Close or pause the culprit — the usual ⌘Q inside the app. If it doesn’t respond, press ⌥⌘Esc and choose Force Quit.
3. Let the Mac cool down. Move the laptop off the bed or your lap to a hard table and clear the vents. Apple recommends a hard, flat surface: on soft ones the fans have to run more.
4. Wait a few minutes and look at kernel_task again. Once the CPU has cooled, the percentage drops by itself.

If it doesn’t drop and there’s nothing heavy in the list, check whether the system complained about heat. pmset -g therm in Terminal shows whether macOS recorded thermal warnings and limited the CPU. More about it, and where to get degrees, is in the guide to Mac temperature.

High kernel_task on a cool Mac

Heat is the main cause but not the only one. The kernel also does the work of drivers, so its time grows when devices are busy: copying to an external drive, a virtual machine, a Time Machine backup. You’ll see it on the other tabs: Disk shows who’s writing, Network shows who’s downloading.

Spikes like these end when the work does. If kernel_task stays high for hours while the Mac is cool and isn’t copying anything:

• restart the Mac — the simplest way to clear a stuck state;
• unplug external devices one at a time — a hub, drives, a display — and watch the percentage;
• update macOS if you haven’t in a while;
• on an Intel Mac, reset the SMC — the System Management Controller, which among other things runs the fans. Apple silicon has no separate reset: according to Apple a restart is enough; the Intel steps depend on the model and are in the same article.

Still no luck — run Apple Diagnostics, which tests the Mac’s hardware (how to run it).

What not to do

• Don’t try to quit kernel_task. It’s the system’s kernel, not an app: the Mac can’t run without it.
• Don’t install utilities that promise to “disable” kernel_task or spin the fans up by hand. Cooling is the system doing its job, and there’s no reason to work around it.
• Don’t go hunting for malware because of a high kernel_task alone. It’s a normal process; an app you aren’t using sitting near the top is more suspicious.

Fans and battery share the same root

High kernel_task, loud fans and fast battery drain usually come from the same thing — heavy CPU or GPU work. If the fans are loud for no obvious reason, go through why your Mac fan is loud; if the battery melts away, see the guide to MacBook battery drain.

In the app

To be clear up front: Mac Resources doesn’t show a process list, temperatures or fans — the widget extension runs in the macOS sandbox. The culprit is found in Activity Monitor.

How the app helps here:

• the menu bar item shows the highest percentage of CPU, memory and GPU and turns red above 80%. Red together with a hot case means heat from load — time to open Activity Monitor;
• the Processor and Last Hour widgets draw a graph for the past hour, so you can see when the load started that woke kernel_task up.

The app is free and runs on macOS 14 and later. If your Mac is slow even without heat, walk through the step-by-step diagnosis.