Which Apps Are Using Too Much of Your Mac's CPU?

Your fans are loud. Your battery is draining fast. The MacBook is hot enough to bother you on your lap. Something is eating CPU, and you’d like to know what.

Activity Monitor will tell you, but only if you know what to look for. Here’s the actual workflow for spotting runaway apps and processes.

Open Activity Monitor

Cmd+Space, type “Activity Monitor”, press return. Or it’s in /Applications/Utilities/Activity Monitor.app.

The first thing to do is sort by CPU usage. Click the % CPU column header. The hungriest processes go to the top.

A few things to know about that column:

• The number is percent of one core. On an 8-core Mac, max possible is 800%. On an M-series Mac with performance + efficiency cores, the math is more complicated but the principle holds: a process showing 200% is using two cores hard.
• Idle Mac processes hover at 0–5%. Anything above 50% sustained is doing real work.
• Spikes are normal. What matters is sustained usage.

What’s normal CPU usage

A healthy Mac at idle:

• kernel_task — 1–10%, doing housekeeping
• WindowServer — 1–5%, drawing the UI
• coreaudiod — 0–2% if audio is playing
• All other processes — under 5%

When you’re using an app:

• The active app — 10–80% depending on what it’s doing
• WindowServer — bumps up if the UI is active
• Helpers and daemons — usually under 5%

When something’s wrong:

• One app at 100%+ for minutes at a time
• A helper or daemon at high CPU when its parent app isn’t doing anything
• kernel_task at 30%+ sustained (often means the Mac is throttling for thermal reasons)
• An app you don’t recognize at high CPU

Common culprits

Some processes regularly show up at the top of the CPU list:

• Browsers. Chrome, Safari, Firefox can each consume 50%+ of a core when running modern web apps. Each tab is a separate process.
• Slack and Discord. Both are Electron-based and can spike to 30%+ when active.
• Spotlight indexing (mds, mdworker). Right after install or major file changes, Spotlight reindexes — can run hot for hours.
• Time Machine (backupd). Backups are intensive.
• Photos (photoanalysisd, mediaanalysisd). Scanning your library for faces and objects.
• Anti-virus tools. Real-time scanners are inherently CPU-heavy.
• Cloud sync. Dropbox, Google Drive, iCloud Drive on initial sync.
• Compiler/build tools. Xcode, Homebrew installs, npm installs all peg cores.

For the first six, the fix is usually waiting — they finish what they’re doing eventually. For the rest, the question is whether the work is something you actually want.

Identifying a runaway process

A runaway is a process that’s using high CPU for no good reason. Telltale signs:

• High CPU when you’re not actively using the app
• Continues after you quit the app (helper not cleaned up)
• Process you don’t recognize and can’t easily Google
• Sudden sustained spike with no corresponding action on your part

When you spot one:

1. Note the process name
2. Check the % CPU trend over a minute
3. Right-click → Inspect to see more detail
4. Look at Disk and Network tabs to see if it’s also doing IO
5. Decide whether to quit it

Make this one clickSweep handles all of this automatically and lets you approve before anything is deleted. Free for macOS →

How to stop a CPU hog

If the process is an app you can quit normally, do that first. Cmd+Q, give it a few seconds.

If it’s a helper or daemon:

1. In Activity Monitor, select the process
2. Click the X button in the toolbar
3. Choose Force Quit if it doesn’t respond to Quit

For processes that respawn (because a LaunchAgent keeps relaunching them), the real fix is finding and disabling the LaunchAgent in ~/Library/LaunchAgents or /Library/LaunchAgents.

When kernel_task is the problem

kernel_task showing high CPU is often a symptom, not the cause. macOS uses kernel_task to soak up CPU cycles when the system is too hot, as a way to throttle other processes and let the Mac cool down.

If you see kernel_task at 30%+ sustained:

• Check ambient temperature. Don’t run a Mac on a couch cushion.
• Check for vent blockage.
• Check if you’re using a USB-C hub that draws a lot of power (some cause unexpected heat).
• Look at what else is running — kernel_task is reacting to other processes generating heat.

The cure is usually thermal: cool down the Mac, then kernel_task calms down too.

Finding background processes you didn’t know were running

Activity Monitor shows everything, including a lot of system processes you’ve never seen. Sort by % CPU and scroll past the top hits — sometimes the interesting ones are at 5–15%, not 100%.

Things to look for:

• Old helpers from apps you’ve uninstalled (orphan LaunchAgents)
• Updaters that run constantly
• Sync clients you forgot you installed
• Anti-virus software you don’t remember setting up
• Browser extensions running their own processes

If you don’t recognize a process, right-click → Open in Finder to see where it lives. Most user-level processes are in /Applications, ~/Applications, or ~/Library/Application Support/<vendor>/.

How to fix the recurring CPU-hog problem

The pattern of “an app keeps spiking even when I’m not using it” is usually fixable:

1. Identify the offender via Activity Monitor.
2. Check whether you actually need the app running in the background — many apps default to “launch at login” without asking.
3. Open System Settings → General → Login Items. Disable anything you don’t need at login.
4. Also check ~/Library/LaunchAgents/ for helpers that bypass the visible login items list.
5. For apps you do need, look in their preferences for an option to disable background activity (Slack, Spotify, OneDrive all have these).

For a serious cleanup, an app like Sweep can identify and kill runaway processes plus surface dead LaunchAgents pointing at apps that no longer exist. The combination usually drops idle CPU by a measurable amount on a Mac that’s been in use for a few years.

There’s a faster waySweep does the same hunt in seconds, with a preview before anything is removed. Try Sweep free →

When the issue is RAM, not CPU

Sometimes the symptom is “Mac feels slow” but the cause is RAM pressure, not CPU. macOS swaps to disk when RAM is full, and disk swaps stall the system in ways that look like CPU issues but aren’t.

Switch to the Memory tab in Activity Monitor:

• Memory Pressure is the gauge. Green = fine. Yellow = high. Red = thrashing.
• Swap Used — non-zero means macOS is using SSD for what should be RAM
• Compressed — macOS compresses inactive memory before swapping; high here is fine

If memory pressure is yellow or red, the fix is to quit memory-heavy apps, not investigate CPU.

Apps that misbehave specifically on Apple Silicon

A few categories cause CPU issues specifically on M-series Macs:

• Intel-only apps running under Rosetta 2. Slower, hotter than native ARM versions.
• Some Electron apps with old Chromium. Newer versions are better.
• Older Java apps without ARM JVMs. Run hot under Rosetta.

If you have an Intel app you use heavily, check if there’s an Apple Silicon native version. The CPU savings are usually significant.

Quick reference

When CPU is high:

1. Open Activity Monitor (Cmd+Space, “Activity Monitor”)
2. Sort by % CPU
3. Identify processes above 50% sustained
4. Quit the app or process if you don’t need it
5. For repeating offenders, check Login Items and LaunchAgents

For background activity:

• Disable unnecessary login items (System Settings → General → Login Items)
• Remove orphan LaunchAgents from ~/Library/LaunchAgents/
• Uninstall apps you don’t use (with their helpers)

If kernel_task is high, it’s probably thermal — cool the Mac, the issue clears.

The Mac equivalent of “have you tried turning it off and on again” is usually closer to “have you tried killing all the helpers from apps you forgot you installed.” Most CPU mysteries dissolve once you actually look at what’s running.