The fastest way to see what's using your processor

Open Activity Monitor, which is built into every Mac. Press Command+Space to open Spotlight search, type "Activity Monitor", and press Enter. When the window opens, click the CPU tab at the top. You will see a list of every program running on your Mac, ranked by how much processor power each one is using right now.

The column labeled % CPU shows the percentage of your processor each program is consuming. If one program shows 80% or higher, that program is the reason your Mac feels slow. If you see several programs each using 10–20%, your processor is being shared among many tasks, which can also slow things down.

Activity Monitor updates in real time, so you can watch the numbers change as you open and close programs. This is the same tool Apple's own support staff use when diagnosing Mac performance problems.

Key Takeaways

  • Activity Monitor is the built-in tool on every Mac for checking CPU usage — find it by pressing Command+Space and typing its name.
  • The CPU tab shows every running program and what percentage of your processor each one is using right now.
  • A single program using 80% or higher is usually the culprit when your Mac slows down.
  • You can force-quit a program that is stuck using too much CPU by selecting it and clicking the stop button.

Understanding the CPU columns in Activity Monitor

Activity Monitor shows several columns of information. The % CPU column is what matters most — it tells you the percentage of your processor's total power that program is using at that moment. On a Mac with a single-core processor, 100% means the program is using all available power. On a Mac with multiple cores (which most modern Macs have), 100% means the program is using one full core.

The User column shows who owns the process — usually your account name. Processes owned by "root" or "system" are part of macOS itself. The Threads column shows how many separate tasks that program is running at once. You do not need to understand threads to fix a slow Mac — just focus on the % CPU number.

By default, Activity Monitor sorts programs by % CPU from highest to lowest, so the biggest processor hog appears at the top. This makes it straightforward to spot the problem without reading every line.

What to do when one program is using too much CPU

If you see a program using 50% CPU or higher and you are not actively using it, that program has a problem. First, try closing it normally — click the program name in the dock and press Command+Q, or use the File menu to quit. Wait a few seconds and check Activity Monitor again to confirm it closed.

If the program does not close, select it in Activity Monitor and click the red circle with an X button in the top left corner of the window. A dialog will ask whether you want to force quit. Click Force Quit. The program will close when ready, though you may lose unsaved work in that program.

After you force-quit a program, restart your Mac and try opening that program again. If it uses excessive CPU every time you open it, the program may be damaged or outdated. Check the App Store or the program's website to see if an update is available. If updates do not help, you may need to uninstall and reinstall the program.

When multiple programs are using moderate CPU

Sometimes you will see five or ten programs each using 5–15% CPU, and together they are slowing your Mac down. This is normal when you have many browser tabs open, are editing video or photos, or are running several programs at once. Your Mac's processor is straightforward busy.

The solution is to close programs you are not actively using. Close browser tabs you do not need. Quit programs running in the background — check the menu bar at the top of your screen for program icons you forgot about. Restart your Mac, which closes everything and gives you a fresh start.

If your Mac is always slow even when you close most programs, your processor may be too old for the work you are doing. Video editing, 3D design, and running many browser tabs at once require newer Macs. If you are doing light work — email, web browsing, documents — and your Mac still feels slow, the problem may be your hard drive or memory instead of your CPU.

Checking CPU usage over time, not just right now

Activity Monitor shows CPU usage at this exact moment. If you want to see what was using your processor an hour ago, Activity Monitor cannot tell you that. However, you can watch Activity Monitor for a few minutes while you work normally, and you will see which programs consistently use the most CPU.

Open Activity Monitor and leave it visible while you use your Mac for five or ten minutes. Do your normal work — open email, browse the web, whatever you usually do. Watch which programs appear at the top of the list repeatedly. Those are the programs that are actually slowing your Mac down during your normal day, not just at one moment.

System processes that use CPU and whether to worry

You will see programs with names like "kernel_task", "WindowServer", "Finder", and "loginwindow" in Activity Monitor. These are part of macOS itself, not programs you installed. It is normal for them to use 5–10% CPU occasionally. If any of them consistently uses 30% or higher, your Mac has a problem that may require a restart or a visit to Apple Support.

Do not force-quit system processes. They keep your Mac running, and closing them can cause crashes or data loss. If a system process is using excessive CPU, restart your Mac first. If the problem continues after a restart, note the name of the process and contact Apple Support or a Mac technician.

Frequently Asked Questions

What does 100% CPU usage mean on a Mac?

It means one core of your processor is completely full. Modern Macs have multiple cores, so 100% CPU does not mean your entire processor is maxed out — it means one core is. If you have an 8-core Mac and see 100% CPU, you still have 7 other cores available. If you see 800% CPU (which the display shows as 800 on some Macs), then all 8 cores are full.

Is it safe to force-quit a program from Activity Monitor?

Yes, it is safe to force-quit any program you installed. You will lose any unsaved work in that program, but you will not damage your Mac. Do not force-quit system processes like kernel_task or WindowServer — those keep your Mac running. If a program is frozen and will not close normally, force-quitting is the correct solution.

Why does my Mac show high CPU usage when I am not doing anything?

Background programs are running. Check Activity Monitor to see which ones. Spotlight indexing, Time Machine backups, software updates, and cloud sync programs like iCloud Drive can all use CPU in the background. If you see a specific program using high CPU, force-quit it or uninstall it. If CPU is spread across many system processes, restart your Mac.

Can I see which websites are using CPU in Safari?

Activity Monitor shows Safari as one program, not individual websites. If Safari is using high CPU, one of your open tabs is the problem, but Activity Monitor cannot tell you which one. Close tabs one at a time and watch the CPU percentage drop to find the culprit. Some websites with auto-playing video or constant updates use much more CPU than others.

Should I worry if CPU usage goes to 100% for a few seconds?

No. Brief spikes to 100% are normal when you open a program, save a large file, or your Mac is doing background work. Worry only if CPU stays at 80% or higher for several minutes while you are not doing anything demanding, or if a single program consistently uses 50% or higher when you are not actively using it.