Find the app that's slowing your Mac
A step-by-step way to find the app behind a slow Mac using Activity Monitor: memory first, then CPU, then energy.
When your Mac feels slow, there is nearly always one or two apps behind it. Activity Monitor can show you which, if you know the order to look in.
The honest answer
Slowness has three common causes: not enough memory for what is open, an app using a lot of processor time, or the Mac holding itself back because it is hot. Check them in that order, because each one points to a different app and a different fix.
Step 1: Memory
- Open Activity Monitor (in Applications, Utilities) and click Memory.
- Look at the Memory Pressure graph at the bottom. Green means memory isn’t the problem, so skip to step 2. Yellow that stays, or red, means keep going.
- Click the Memory column header to sort high to low.
- Look for an app that is far larger than you’d expect. A chat app at several GB, or a browser helper with an enormous footprint, is a red flag. Compare with what you remember: an app that was much smaller a few days ago has grown.
- Also check Swap Used. If it keeps climbing, the large app is the likeliest cause. See What swap is and when it hurts.
What to do: save your work, quit that app with ⌘Q, and open it again. An app that has been open for days often returns to a fraction of its size. If it grows back fast, the app has a leak, and updating it or reporting it to its maker is the real fix.
Step 2: CPU
- Click the CPU tab and sort by % CPU.
- Watch for an app using a large share for minutes at a time while you are not using it. An app that is busy only when you use it is behaving normally.
- Some work is legitimate: a backup, a photo library analyzing, Spotlight indexing after an update. These settle on their own. If an app sits at the top for a long time with nothing obvious going on, quit it.
Processes owned by macOS appear here too: kernel_task, WindowServer and others. kernel_task, WindowServer and other processes explained covers them, because the fix is rarely “quit it”.
Step 3: Energy and heat
- Click the Energy tab and sort by Energy Impact.
- A fanless MacBook Air that feels warm and slow often has a background app working constantly. The Energy tab names it.
Check, don’t guess
Slowness can look like a memory problem and be a CPU one, or the reverse. Opening the right tab first saves you from fixing the wrong thing. For Apple’s reference on what each column means, see the Activity Monitor guide.
How Hedroom does it
Hedroom does this watching for you, continuously, and learns what is normal for each app on your Mac. After a few hours it can say things like “this app is 3.7 times its usual size” rather than leaving you to remember. For a background app using a lot of CPU for several minutes, it tells you which one. It then offers one fix, such as relaunching the app or moving it to the efficiency cores. It never touches macOS’s own processes, apps you are using, apps on a call or backups. Afterward you get a receipt that shows whether it made a difference.
Want Hedroom to do the checking? It reads memory pressure and swap for you, names the app that matters, and gives every fix a receipt. See how the free trial works or join the waitlist.