1. Low disk space
One of the most common causes of Mac slowdown is low disk space. For optimal performance it’s recommended that you have at least 10% free storage, but 25% is even better.
Fix: Delete files you don’t use. If you have a Mac optimization app handy, you can quickly remove cache, log and junk files.
2. Low RAM
When your Mac runs out of physical memory, it will use the built-in hard drive (flash drive) as virtual memory.
Fix: Open Activity Monitor, select the Memory tab and analyze the memory pressure of the processes listed, and quit any apps you’re not using.
3. High CPU usage
This could be due to an unresponsive app or just a resource hog, but the end result is a very slow and overheating Mac.
Fix: Open Activity Monitor, select the CPU tab and have a look at the bottom of that tab. If the “% Idle” is consistently below 60% for several seconds, check which processes are eating CPU power and quit them by clicking the “X” button.
4. Desktop full of icons
Saving files on the desktop is handy, but after a while it may become a headache. Desktop icons are drawn as a window, and macOS renders a preview of the icons and contents, so these icons can become an unnecessary resource hog.
Fix: Save the files in a dedicated folder. This can even be done with Screenshots when using OnyX.
5. Failing hard drive
If your hard drive is reaching the end of its lifecycle, you’ll hear unusual sounds and clicks coming from inside your Mac. You’ll also notice various errors when running Disk Utility’s First Aid.
Fix: First, it’s good to check your startup disk’s health from time to time using Disk Utility or with third party Mac optimization software. Secondly, back up your data and prepare to upgrade your Mac to an SSD.
6. Too many apps running
Sometimes we forget to quit apps we’re not using, and since the physical resources of macOS are limited, this obviously slows the computer down.
Fix: Check the icons in the Dock and quit the apps you’re not using.
7. FileVault disk encryption enabled
This isn’t necessarily an issue for newer Macs with SSDs, but those with a hard drive will definitely feel it. FileVault will encrypt all data on your disk, and every new process adds another burden to the system, causing slowdown.
Fix: Turn off FileVault by hitting Settings > Security & Privacy > FireVault tab.
8. Browser with lots of extensions
When customizing the browsing experience, you might end up with tons of plugins and add-ons that ultimately overload the web browser and affect the overall user experience.
Fix: Launch your favorite browser and disable extensions you don’t use on a daily basis. You can do this easily with third party Mac optimization apps such as CleanMyMac.
9. Mail overload
We love Apple’s Mail app because it’s reliable, but when it needs to load many years’ worth of emails… well, it will affect your system performance drastically, especially when loading and preserving huge file attachments.
Fix: Remove downloaded mail attachments (you can download them anytime) with the help of a third party Mac optimization app. Or you can create rules for erasing emails after a certain number of days.
10. Outdated operating system
This should be the last cause of system slowdown, but if you don’t pay attention to the software updates Apple is pushing out you might end up with a slow Mac.
Fix: Keep your Mac up to date and reboot after installing the latest software.
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