One of the most common questions I hear from clients is, “Why is my Mac slow?” This seemingly simple question can have an array of possible causes. Below are a few things you can easily check. One of these could help you identify, or maybe resolve, the cause of your Mac’s slowness.

Before you check or change anything, make sure you have a full backup of your Mac. Next, pay attention to your Mac’s slowness and try to describe it as well as possible. Is your Mac slow to start up or shutdown? Is only one application particularly slow, such as Microsoft Word or Adobe Photoshop? Is the problem limited to Internet activity like viewing web pages or sending and receiving email messages? Do you see lots of spinning beach balls? Are Finder windows slow to open or update? Is your Mac only slow when Time Machine or some other backup application is running?

Restart Your Mac

I recommend that you restart your Mac weekly. If it’s been a long time since you’ve restarted your Mac, do this and see if your Mac’s performance improves. If so, then restart your Mac more regularly. It’s also possible that your Mac might be suffering from not enough memory, but don’t confuse a computer’s memory with its storage capacity. You can use Activity Monitor to help determine if your Mac could benefit from having more memory installed, use either this Macintosh How To article or the X Lab’s article. Activity Monitor was significantly updated in OS X Mavericks (10.9). If you’re using Mavericks or a newer version of OS X, please read this article from Apple.

Is Your Hard Drive Nearly Full?

If your Mac’s hard drive is nearly full then this can dramatically decrease its performance. I typically recommend keeping a hard drive less than 90% full. To check, click on the Apple menu and choose About This Mac. From that window, click the button labeled “More Info…” This will open the System Information app. Click on the Storage tab across the top left of the window. Note the drive’s capacity and amount of free space. If your drive is too full, you’ll want to move some data to another drive or use OmniDisksweeper to locate stuff you can delete.

Is Your Hard Drive Failing?

Every hard drive will eventually fail. That’s why it’s so important to set up a robust backup system. When a drive fails it can occur suddenly or slowly. A slowly failing drive can cause your Mac to run very slowly which could include: slow startup, slow opening of windows, delays when opening applications and lots of spinning beach balls. Use Onyx or SMARTUtility to check the health of your Mac’s internal hard drive.

Is Your Internet Connection Slow?

If your Mac’s slowness occurs when viewing web pages or receiving email messages, then check the speed of your Internet connection. You can go TestMySpeed or SpeedTest. Both of these sites require Adobe Flash. These web sites test the speed of your Internet connection by downloading and then uploading a file. Run the tests on different days and at different times to see if you notice much variation. For comparison, it’s also useful to have a record of your speed test results when things are working well.

If you think your Internet connection is slow, test the speed on other computers on your network to see if all computers reports similar speeds. You could restart your wireless router to see if this helps. If not, then restart your cable or DSL modem.

If the slow web browsing problem is limited to only one Mac then restart your web browser, Safari, Chrome, or whichever one you use.

Is Your Mac Slowed By An Anti-Virus Application?

Anti-Virus and other security applications often slow computers since they run in the background and continually monitor things and check files as they are open. If you have an anti-virus application like Norton Anti-Virus, Intego VirusBarrier, or Sophos Anti-Virus installed, see if there’s an easy way to temporarily disable this application. Turn it off for a few hours or a day to see if this makes a difference in your Mac’s performance.

Is your Mac Slowed by Adware Or Some Sort Of Malware?

Use DetectX or MalwareBytes for Mac to remove the offending software (adware or malware) from your Mac.

Safe Boot Your Mac To See If It Runs Faster In Safe Mode

Use the instructions in this other Tech Tip to learn how to Safe Boot your Mac. Once you’ve safe booted your Mac then use it for a little while and see if your Mac’s performance is noticeably different. If so, then the most likely cause is one of the third-party pieces of software that has been disabled by the Safe Boot. If you know how to locate which software is started automatically during a normal startup review these items and see if you can pinpoint the problem. Pointer: check the different LaunchAgent, LaunchDeamons, StartupItems folders.

Use Activity Monitor To Check The Mac’s Processor (ask CPU)

The Activity Monitor lets you peek behind the curtain and view an array of details about your Mac’s activity. One thing it lets you monitor is the activity of the processor, also known as the central processing unit (CPU). You can see a list of all open applications and background processes and see how much of the processor’s attention is being used by each. This can help you find if there is an errant application or process that is gumming up the works. Read this detailed article from The X Lab about how to use Activity Monitor.