The fastest way to see what's using your processor
Open Activity Monitor — the built-in tool that shows you exactly which programs are consuming your Mac's processing power. Press Command+Space, type "Activity Monitor", and press Enter. The window that opens shows every running process and how much CPU each one is using as a percentage.
The CPU column is what you're looking for. If a single program shows 80% or higher, that's why your Mac feels slow — one thing is hogging the processor. If the total of all percentages adds up to consistently over 90%, your Mac is working at near capacity and will feel sluggish no matter what you're doing.
Activity Monitor updates in real time, so you'll see the numbers change as programs start and stop working. The default view shows processes from your user account. If you want to see everything running on the Mac, including system processes, click the dropdown menu at the top that says "My Processes" and select "All Processes".
Key Takeaways
- Activity Monitor is built into every Mac and shows CPU usage for every running program without installing anything.
- The CPU column displays each program's processor use as a percentage, and anything consistently above 80% is likely causing slowness.
- You can force-quit programs that are stuck using high CPU by selecting them and clicking the stop button, though unsaved work will be lost.
- The System tab in Activity Monitor shows overall CPU load and how many cores your Mac is using, which helps you understand whether a single program or multiple programs are the problem.
Understanding the numbers Activity Monitor shows
Each program listed shows a percentage next to its name in the CPU column. This percentage means how much of your Mac's total processing power that program is using right now. A Mac with four processor cores can theoretically use up to 400% total CPU (100% per core), so a program showing 50% is using half of one core.
The "% CPU" column updates every second or so. A program that jumps between 5% and 90% is doing something intensive sometimes and resting other times — that's normal. A program stuck at 95% for minutes at a time is the real problem.
At the bottom of the Activity Monitor window, you'll see "System Memory" and other stats. Look for the line that shows how many CPU cores are in use. If your Mac has 8 cores and the display shows "8 cores", your processor is fully loaded. If it shows "2 cores", only a quarter of your Mac's power is being used, so slowness is coming from something else — usually your hard drive or internet connection.
Finding which program is slowing down your Mac
Click the CPU column header to sort all programs by how much processor they're using. The biggest CPU hogs appear at the top. This makes it obvious which single program is the problem, if there is one.
Some programs you'll see are normal: Finder, Spotlight, and WindowServer are Mac system processes that do background work. If you see a program you recognize — like Chrome, Slack, or Photoshop — using 70% or more for more than a few seconds, that program is either stuck or doing something intensive like rendering video or processing a large file.
If you don't recognize the program name, search for it online before doing anything. Some system processes have cryptic names like "kernel_task" or "WindowServer" that sound suspicious but are actually essential. Closing the wrong thing can cause your Mac to crash or become unstable.
How to stop a program that's using too much CPU
Select the program in the list and click the stop button (the circle with an X) in the top-left corner of the Activity Monitor window. A dialog will appear asking whether you want to "Force Quit" the program. Click "Force Quit" to shut it down immediately.
Force-quitting closes the program without saving any open documents, so you will lose unsaved work. If the program is responsive, it's better to quit it normally — click the program's name in the top menu bar and select "Quit [Program Name]". This gives the program a chance to save what it's working on.
After you force-quit a program, watch Activity Monitor for a few seconds to confirm the CPU percentage drops. If the same program immediately starts using high CPU again, the problem is that the program itself is broken or stuck in a loop. Restart your Mac, and if the problem returns, uninstall and reinstall the program or contact the developer.
Checking CPU usage over time with the System tab
Click the "System" tab at the top of Activity Monitor to see a graph of your Mac's CPU usage over the last minute. This view is useful if you want to understand patterns — whether your Mac is consistently maxed out or just spiking occasionally.
The graph shows CPU usage as a line that moves up and down. If the line is flat at the bottom, your Mac is idle. If it's constantly near the top, something is always demanding processor power. The colored sections of the graph represent different types of CPU work: user processes (the programs you run), system processes, and idle time.
This tab also shows how many threads are running and the average load. The load number tells you how much work is queued up waiting for the CPU. A load of 4 on a 4-core Mac means the processor is fully busy. A load of 8 on the same Mac means some work is waiting and the Mac is struggling to keep up.
Why your Mac might show high CPU usage even when nothing seems to be running
Spotlight indexing, Time Machine backups, and software updates can all use significant CPU in the background. If you see high CPU but no obvious culprit, check whether your Mac is currently backing up or indexing. Look for "mds" (Spotlight), "backupd" (Time Machine), or "softwareupdate" in the process list.
These background tasks are necessary and usually finish on their own. If Spotlight indexing is using 80% CPU, your Mac will be slow until it finishes, which can take hours on a full drive. You can pause Spotlight indexing by going to System Settings > Siri & Spotlight > Exclude folders, but it will resume when you restart.
If you see "kernel_task" using very high CPU (above 50%), your Mac may be overheating and throttling the processor to cool down. Shut down your Mac, let it rest for 10 minutes, and check whether the problem returns. If it does, the cooling system may need service.
Using Terminal if Activity Monitor won't open
If Activity Monitor itself won't open or is frozen, you can check CPU usage from Terminal. Press Command+Space, type "Terminal", and press Enter. Type this command and press Enter: top -l 1 | head -20
This displays the top CPU-using processes in a text format. The first column shows the process ID, and the third column shows CPU percentage. Press Control+C to stop the command and return to the prompt.
Terminal is more technical than Activity Monitor, but it works when the graphical tools are stuck. If you need to run this command regularly, you can type top alone to get a live-updating display similar to Activity Monitor. Press "q" to quit.
Frequently Asked Questions
Is it normal for my Mac to show 100% CPU usage sometimes?
Yes, brief spikes to 100% are normal when you're doing something intensive like exporting video or opening a large file. The problem is when CPU stays above 80% for minutes at a time while you're doing nothing. That means a program is stuck or misbehaving.
What does "kernel_task" do and why is it using so much CPU?
Kernel_task is a system process that manages hardware. High kernel_task usage usually means your Mac is overheating and the system is throttling the processor to cool down. Check whether your Mac feels hot, and make sure the vents aren't blocked by dust or objects.
Can I close programs from Activity Monitor without losing my work?
Only if you use the regular Quit option, not Force Quit. To quit normally, select the program and click the stop button, then choose "Quit" instead of "Force Quit". The program will save its work before closing. Force Quit closes immediately without saving.
Why does Activity Monitor itself sometimes use high CPU?
Activity Monitor uses CPU to constantly update the list of running processes. If you leave it open and set it to update very frequently, it can become part of the problem. Close Activity Monitor when you're done checking, or set it to update less often by going to View > Update Frequency.
What's the difference between CPU usage and memory usage?
CPU is the processor — how fast your Mac is working right now. Memory is RAM — how much space programs are taking up. High CPU makes your Mac feel slow immediately. High memory makes your Mac slow down over time as it runs out of space and starts using the hard drive as backup storage.