kernel_task using high CPU on Mac: what it means and what to do
kernel_task takes CPU time to cool the Mac down, so it is a symptom, not the cause. How to find what is heating the Mac and bring kernel_task back down.
- kernel_task is part of macOS; one of its jobs is to keep the CPU from overheating by taking CPU time away from busy apps.
- High kernel_task CPU is a symptom of heat, not the cause, so quitting or killing kernel_task is not possible and would not help.
- Open Activity Monitor, sort by % CPU and quit the app that was using the most CPU before kernel_task went up.
- Then remove the heat: clear the vents, use the Mac on a hard surface, and check whether a charger or external display is adding load.
What kernel_task is#
kernel_task is the name Activity Monitor gives to the macOS kernel, the core of the operating system. It is always running and it always uses some CPU and memory. It only becomes a problem when it suddenly takes 100% or more of the CPU and the Mac slows down.
Apple explains the reason directly: one of kernel_task's functions is "to help manage CPU temperature by making the CPU less available to processes that are using it intensely." When the CPU gets too hot, kernel_task claims CPU time so that other apps cannot use it, and the CPU cools down. Apple adds that kernel_task "responds to conditions that cause your CPU to become too hot, even if your Mac doesn't feel hot to you. It does not itself cause those conditions."
So kernel_task at high CPU means something is making the Mac hot. The fix is to find and remove that.
Step 1: find the app that is causing the heat#
- Open Activity Monitor (Applications › Utilities, or ⌘ Space and type Activity Monitor).
- Click the CPU tab, then the % CPU column so the busiest processes are on top.
- Ignore kernel_task. Look at the next few lines: a browser tab, a video export, a game, a stuck background process.
- Select it and click the Stop button (the ✕ in the toolbar), then Quit. If it does not respond, choose Force Quit.
Watch kernel_task for a minute or two. If it falls back to a few percent, you found the cause.
You can also see the top processes in Terminal:
top -o cpu -n 10 -l 2 -stats pid,command,cpu | tail -11
This samples twice and shows the 10 busiest processes. It only reads. When we ran it on our test Mac, the top of the list was:
| Process | % CPU |
|---|---|
| kernel_task | 39.8 |
| WindowServer | 29.9 |
| ReportCrash | 29.9 |
| qemu-system-aarch64 (a virtual machine) | 12.8 |
kernel_task was the symptom. The causes were below it: a virtual machine running in the background and ReportCrash, the macOS process that writes a report each time an app crashes. Quitting the virtual machine and finding the crashing app (its reports are in Console › Crash Reports) is the fix, not touching kernel_task.
Step 2: remove the heat#
If no single app stands out, the problem is cooling:
- Check the vents. MacBooks pull air in at the hinge and the sides. Dust there raises temperatures over time.
- Use a hard, flat surface. A bed, sofa or lap blocks airflow.
- Watch the room temperature. Direct sun or a hot room is enough to start throttling during heavy work.
- Restart. A restart clears processes that got stuck in a loop and keeps the CPU busy.
Step 3: check chargers and external displays#
Two hardware setups come up again and again in reports about kernel_task:
- External displays. Each extra display, especially at high resolution or a high refresh rate, adds GPU and CPU work and heat. Try the Mac without the display for a few minutes to compare.
- Charging side on Intel MacBook Pros. Many owners of 2016–2020 Intel MacBook Pros report that charging from the left-side ports runs hotter and triggers kernel_task, and that moving the charger to the right side helps. Apple has not documented this, but it is free to try.
Our test Mac, an Apple silicon MacBook Pro, was driving its built-in display plus a second 1080p display at 170 Hz, which is why WindowServer sat near 30% CPU. If WindowServer is the process at the top for you, read WindowServer high CPU on Mac.
Step 4: if it keeps happening#
- Start in safe mode once. Safe mode loads only what macOS needs; if kernel_task stays calm there, a login item or extension is the likely cause. Apple describes how in Start up your Mac in safe mode.
- Check login items in System Settings › General › Login Items & Extensions and turn off anything you do not recognise.
- Free up disk space. A nearly full disk makes macOS work harder with swap files. Our storage checklist covers that.
- Run Apple Diagnostics if the fans are silent while kernel_task is high, which can point to a fan or sensor problem.
Do not use apps or scripts that claim to "disable" kernel_task or remove macOS thermal files. They work around the safety system that protects the CPU and can leave the Mac running too hot.
For other reasons a Mac feels slow, see the slow Mac guides.
FAQ
Can I quit or kill kernel_task?
No. kernel_task is the macOS kernel itself, so Activity Monitor will not quit it. It lowers its activity on its own once the CPU cools down.
Is kernel_task a virus?
No. It is a built-in macOS process that every Mac runs. Apple documents it as one of the ways macOS manages CPU temperature.
Why does kernel_task go up when I connect an external monitor?
Driving an extra display, especially a high-resolution or high-refresh one, adds work for the GPU and CPU and more heat. On Intel MacBook Pros the charging port side has also been widely reported to matter, though Apple has not documented it.
Does kernel_task high CPU happen on Apple silicon Macs?
It can, but far less often, because M-series chips run cooler. On Apple silicon, high CPU from another process or WindowServer is a more common cause of a slow Mac.
Sources
- Oct 12, 2026: First published. Steps checked in Activity Monitor on macOS 26.3.