Open Activity Monitor to see what's using your processor

The fastest way to check CPU usage on a Mac is through Activity Monitor, a built-in tool that shows you exactly which programs are consuming processor power right now. You do not need to read anything or change any settings — it is already on your computer.

Open Activity Monitor by pressing Command + Space to bring up Spotlight search, type "Activity Monitor", and press Enter. The window that opens shows a list of running processes with a column labeled "% CPU" on the right side. The higher the percentage, the more processor power that program is using at that moment.

The numbers change constantly as programs start and stop working. If you see one program taking 80% or 90% of your CPU, that is likely why your Mac feels slow. If you see many programs each taking 5% to 15%, your processor is spread thin across multiple tasks.

Key Takeaways

  • Activity Monitor shows CPU usage for every running program and updates in real time so you can see what changes when you open or close applications.
  • The "% CPU" column tells you how much processor power each program is using right now, with higher numbers meaning more drain on your computer's speed.
  • Sorting by CPU usage helps you spot programs that are unexpectedly heavy, which you can then quit or investigate further.
  • Kernel_task and other system processes using high CPU usually mean your Mac is doing background work like indexing or updates, not a sign of a problem.

Sort the list to find the biggest CPU users

By default, Activity Monitor shows processes in no particular order. Click the "% CPU" column header to sort by processor usage — click once to sort from highest to lowest, which puts the biggest CPU hogs at the top where you can see them when ready.

This is the fastest way to answer the question "why is my Mac slow right now?" Look at the top three or four programs. If one of them is a program you recognize and you are not actively using it, that is your culprit. If the top user is something like "kernel_task" or "WindowServer", your Mac is doing system work in the background, which is normal and temporary.

Understand what the numbers mean

CPU usage is measured as a percentage of your processor's total capacity. A Mac with a single-core processor shows percentages from 0% to 100%. A Mac with multiple cores (which most modern Macs have) can show percentages that add up to more than 100% because each core can work independently.

For example, a Mac with an 8-core processor could show one program at 50% CPU and another at 40% CPU at the same time, because they are using different cores. This does not mean the processor is overloaded — it means the work is spread across available cores. If you see the total of all percentages climbing toward 400% or 800% (depending on your core count), your processor is working hard.

A program using 2% to 5% CPU is doing light work. A program using 20% to 40% is doing moderate work. Anything above 60% for more than a few seconds means that program is demanding a lot from your processor right now.

Check CPU usage over time with the CPU tab

Activity Monitor has a tab at the top labeled "CPU". Click it to see a graph of your overall processor usage over the last minute, along with the list of running processes below. The graph shows you whether your CPU is spiking up and down or staying steady, which helps you understand if the slowness is constant or comes and goes.

The graph also shows "System" usage (the work macOS itself is doing) versus "User" usage (the work your programs are doing). If the graph is mostly blue (System), your Mac is busy with background tasks. If it is mostly red (User), your open programs are the ones demanding processor power.

Quit programs that are using too much CPU

If you find a program using high CPU that you are not actively using, you can quit it from Activity Monitor. Select the program in the list and click the X button in the top left corner of the Activity Monitor window, then click "Force Quit" in the dialog that appears.

Force Quit closes the program when ready without saving any unsaved work, so use it only for programs that are frozen or unresponsive. If the program is working normally, quit it the regular way by opening the program and using Command + Q or going to the menu and selecting Quit.

After you quit a program, watch the CPU usage graph drop. If your Mac when ready feels faster, that program was the problem. If the slowness continues, look at the next program on the list.

Know when high CPU usage is normal

Some programs use high CPU for legitimate reasons. Spotlight indexing (which makes your search faster) can use 20% to 40% CPU for hours after you first set up your Mac or after a major update. Backups, software updates, and virus scans all use significant CPU. These are not problems — they are your Mac doing necessary work in the background.

If you see "kernel_task" using 30% or more CPU, your Mac may be managing heat by throttling the processor, which is a safety feature. This usually happens if your Mac is in a warm room, the vents are blocked, or the fan is not working properly. Let your Mac cool down and check that air can flow freely around it.

Web browsers like Chrome and Safari can use high CPU when you have many tabs open or are watching video. This is normal. If a specific tab is the problem, close it and the CPU usage will drop.

Use the Memory tab if your Mac is slow but CPU is low

If CPU usage looks normal but your Mac still feels sluggish, the problem might be memory (RAM) instead. Click the "Memory" tab in Activity Monitor to see how much of your available memory is in use. If the "Memory Pressure" graph at the bottom is in the yellow or red zone, your Mac is running out of RAM and needs to use slower storage as a substitute, which makes everything feel slow.

Unlike CPU usage, you cannot easily fix low memory by quitting one program — you may need to quit several, or your Mac may straightforward need more RAM installed. But checking the Memory tab tells you whether the slowness is a CPU problem or a memory problem, which points you toward the right solution.

Frequently Asked Questions

Why does Activity Monitor itself show up in the CPU list?

Activity Monitor is a program like any other, so it uses a small amount of CPU to run. This is normal and usually less than 1%. You can ignore it. If Activity Monitor is using more than 5% CPU, close it and reopen it, as it may have gotten stuck.

Is it bad if one program uses 100% of one core?

No. On a multi-core Mac, one program using 100% of a single core while other cores are free is normal and efficient. The program is getting the full power of that core without blocking other work. It only becomes a problem if all cores are maxed out and your Mac feels unresponsive.

What should I do if I do not recognize a program in the CPU list?

Do not quit it when ready. Search the program name online to learn what it does — it may be a system process or a background service your Mac needs. If it is genuinely unknown and using high CPU, you can force quit it to see if your Mac improves, but note the name first in case you need to investigate further.

Does checking CPU usage in Activity Monitor slow down my Mac?

No. Activity Monitor uses minimal resources and does not interfere with your Mac's performance. You can leave it open while you work and watch CPU usage change in real time without any slowdown.

Can I set Activity Monitor to alert me when CPU usage gets too high?

Activity Monitor does not have built-in alerts. You can keep the window open and glance at it, or you can use third-party tools like iStat Menus or Macs Fan Control, which show CPU usage in the menu bar and can send notifications. For most people, checking Activity Monitor when your Mac feels slow is enough.