Check CPU usage in Activity Monitor, the built-in Mac tool that shows which programs are using your processor right now

Your Mac's CPU (central processing unit) is like the brain of your computer — it handles every calculation and instruction. When your Mac feels slow or the fan kicks into overdrive, CPU utilization is often the culprit. The fastest way to see what is happening is to open Activity Monitor, a program that comes with every Mac and shows you exactly which apps are consuming processor power.

Activity Monitor displays CPU usage as a percentage. If you see numbers above 80 percent consistently, something is working harder than it should. If you see 100 percent, your Mac is maxed out and will feel sluggish. The goal is to identify which program is responsible so you can decide whether to close it, restart it, or investigate why it is behaving that way.

Key Takeaways

  • Open Activity Monitor by pressing Command+Space, typing "Activity Monitor", and pressing Enter.
  • Click the CPU tab to see which programs are using the most processor power, ranked from highest to lowest.
  • Look at the percentage in the %CPU column — anything above 50 percent for a single app usually means something is wrong.
  • If a program is stuck using high CPU, select it and click the stop button (circle with an X) to force it to close.
  • The System (kernel_task) process using high CPU often means a hardware issue or macOS background task, not a user program.

Opening Activity Monitor on your Mac

The fastest route is the keyboard shortcut. Press Command+Space to open Spotlight search, type "Activity Monitor", and press Enter. The program opens in seconds.

If you prefer clicking, open Finder, go to Applications, then Utilities, and double-click Activity Monitor. Either way, a window appears showing all running processes on your Mac.

Reading the CPU tab and understanding the numbers

When Activity Monitor opens, you are already on the CPU tab by default. You will see a list of programs with several columns. The one that matters most is %CPU, which shows what percentage of your processor each program is using right now.

The list is sorted by CPU usage, with the heaviest users at the top. A program using 2 to 5 percent is normal background work. A program using 20 to 30 percent is doing something active — like playing video or rendering. A program using 50 percent or higher for more than a few seconds usually means it is stuck or malfunctioning.

You will also see a column called Threads, which shows how many parallel tasks that program is running. More threads does not always mean more CPU use, but it can help explain why a program is working hard. For most troubleshooting, focus on the %CPU column and ignore the rest.

Identifying which program is using the most CPU

Scan the top of the list. The program at the very top is using the most CPU right now. If it is something you recognize and expect — like Safari if you have 20 tabs open, or Xcode if you are compiling code — then your Mac is working as designed.

If the top program is something you did not start, or something that should be idle, that is your problem. Common culprits include web browsers with runaway tabs, video editing software that is still rendering in the background, or cloud sync programs like Dropbox or Google Drive that are indexing files.

Click on any program in the list to highlight it and see more details below. The bottom of the Activity Monitor window shows additional information like memory use and disk activity for that specific program.

Stopping a program that is using too much CPU

If you have identified a program that is stuck or misbehaving, you can force it to close from Activity Monitor. Select the program by clicking on it once, then click the stop button — it looks like a circle with an X inside it — in the top left corner of the Activity Monitor window.

A dialog box will appear asking whether you want to "Force Quit" the program. Click "Force Quit" to close it immediately. This is stronger than the normal quit command and will shut down the program even if it is frozen or not responding.

After you force quit a program, watch the CPU usage drop. If it goes back to normal, the program was the problem. If CPU usage stays high, another program is responsible, and you need to look further down the list.

Understanding system processes and kernel_task

You will see several programs in Activity Monitor that you did not start yourself. These are system processes that run in the background to keep your Mac functioning. Most use very little CPU — under 1 percent. Some common ones are Finder, Spotlight, and loginwindow.

One process you might see using high CPU is called kernel_task. This is the core of macOS itself, not a user program. If kernel_task is consistently above 50 percent, it usually means your Mac is doing heavy background work like indexing files, backing up to iCloud, or running a security scan. It can also mean your Mac is overheating and throttling the CPU to cool down, or that a hardware component is failing.

If kernel_task stays high for hours, restart your Mac. If the problem returns immediately after restart, your Mac may have a hardware issue and you should contact Apple Support or visit an Apple Store.

Checking CPU usage over time with the CPU History graph

At the bottom of the Activity Monitor window, you will see a graph showing CPU usage over the last minute or so. This graph updates in real time and shows you whether CPU usage is climbing, dropping, or staying steady.

If the graph spikes suddenly when you open a program, that is normal — the program is starting up. If the graph stays flat at the top (near 100 percent), your Mac is under constant load. If the graph shows a sawtooth pattern with regular spikes, a program is doing periodic work, like checking for email or syncing files.

The graph is useful for spotting patterns. If you see a spike every few minutes, you can note the time and then look at the process list to see which program is active at that moment.

Frequently Asked Questions

Why is my Mac using 100 percent CPU when I am not doing anything?

Something is running in the background. Open Activity Monitor and look at the top of the CPU list. Common causes are Spotlight indexing (especially after a restart or file transfer), cloud sync programs catching up, antivirus software scanning, or a browser with many tabs. If you see kernel_task at the top, your Mac may be overheating or running a system update.

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

Yes, force quitting closes the program but does not damage your Mac. You may lose unsaved work in that program, so save your files in other programs first if you can. Force quit is safe to use and is often the fastest way to fix a frozen or stuck program.

What does the System Memory tab show, and is it different from CPU?

The System Memory tab shows RAM usage, not CPU usage. They are separate resources. High memory use means your Mac is running out of RAM, which can make it slow. High CPU use means a program is working hard. You can have high CPU with low memory, or high memory with low CPU. Check both tabs if your Mac is slow.

Should I close programs to lower CPU usage?

Only close programs that are using high CPU unexpectedly. If Safari is using 40 percent because you have 50 tabs open, closing some tabs will help. If a program is using high CPU and you do not need it, close it. But closing programs you are actively using will not improve performance — it just stops you from using them.

Can I see CPU usage without opening Activity Monitor?

Yes. Click the Control Center icon (usually in the top right corner of your menu bar), then look for CPU or system stats. Some Macs show a quick CPU meter there. You can also add a CPU widget to your Mac's dashboard by clicking the plus icon in Notification Center. But Activity Monitor gives you the most detail about which specific program is responsible.