What causes a computer to slow down and how to fix it

A slow computer usually comes from one of three things: too many programs running at once, a hard drive that is nearly full, or malware taking up resources. The fastest fix is to close programs you are not using, delete files you do not need, and run a malware scan. Most of the time, one of these three steps will bring your speed back.

Before you start, restart your computer. This clears temporary files and stops programs that have been running in the background. If the slowness stops after a restart, you have found your answer — something was using too much memory. If it comes back within a few hours, move to the steps below.

Key Takeaways

  • Restart your computer first; this solves slowness caused by programs running in the background and takes only a few minutes.
  • Check how much free space is left on your hard drive — if it is below 10 percent of total capacity, delete old files or move them to an external drive.
  • Open Task Manager on Windows or Activity Monitor on Mac to see which programs are using the most memory and CPU, then close the ones you do not need.
  • Run a malware scan using Windows Defender (built into Windows) or a third-party scanner like Malwarebytes to catch infections that slow your system.
  • Disable startup programs that launch automatically when you turn on your computer, since each one takes memory and slows your boot time.

Check how much hard drive space you have left

A hard drive that is almost full will slow down your computer because the system cannot write temporary files. On Windows, right-click your C: drive, select Properties, and look at the pie chart. On Mac, click the Apple menu, select About This Mac, then Storage. If the free space bar is smaller than the used space bar, you are running low.

If you have less than 10 percent free space, delete files you no longer need. Start with your Downloads folder — most people leave old installers and documents there for months. Then check your Documents, Pictures, and Desktop folders. Move large files like old videos or photo backups to an external hard drive or cloud storage like Google Drive or OneDrive.

If you cannot find enough files to delete, uninstall programs you do not use. On Windows, go to Settings > Apps > Apps & features, find the program, and click Uninstall. On Mac, open Applications, drag unused programs to the Trash, and empty it. Uninstalling frees up space and removes programs that might be running in the background.

See which programs are using the most memory

Task Manager on Windows and Activity Monitor on Mac show you exactly which programs are slowing your computer down. On Windows, press Ctrl + Shift + Esc to open Task Manager. On Mac, press Command + Space, type Activity Monitor, and press Enter. Look at the CPU and Memory columns to see which programs are using the most resources.

If you see a program using 50 percent or more of your CPU or memory and you are not actively using it, close it. Right-click the program in Task Manager and select End Task. On Activity Monitor, select the program and click the X button at the top. If the same program keeps using high resources every time you restart, uninstall it — it may be broken or designed to run constantly in the background.

Some programs, like Windows Update or antivirus scans, use high resources temporarily while they work. If you see one of these running, wait 10 to 15 minutes and check again. If the resource use drops back to normal, the program is fine.

Scan for malware and viruses

Malware and viruses can run hidden in the background and consume memory and CPU power. Windows comes with Windows Defender, which is built in and runs automatically. To run a manual scan, click the Windows icon, type Windows Defender, and open Windows Security. Click Virus & threat protection, then Scan options, select Full scan, and click Scan Now. A full scan takes 30 minutes to an hour.

If you want a second opinion or suspect a serious infection, read Malwarebytes from malwarebytes.com. The free version scans and removes malware. Install it, open the program, and click Scan. Restart your computer when the scan finishes.

If a scan finds malware, let the program remove it automatically. Restart your computer afterward. If slowness continues after a full scan and removal, the malware may have damaged system files — in that case, contact a local computer repair shop or call your computer manufacturer's support line.

Turn off startup programs that launch automatically

Every program set to launch when you start your computer uses memory and slows your boot time. On Windows, press Ctrl + Shift + Esc to open Task Manager, then click the Startup tab. You will see a list of programs with a Status column showing Enabled or Disabled. Right-click any program you do not need to start automatically and select Disable.

On Mac, click the Apple menu, go to System Settings, then General, then Login Items. You will see a list of programs that open at startup. Click the minus sign next to any program you want to remove. Be careful not to disable programs you actually use — focus on things like cloud storage apps, messaging programs, or games that you do not need running all the time.

After you disable startup programs, restart your computer. You should notice your computer starts faster and feels more responsive while you work.

Update your operating system and drivers

Outdated software can cause slowness and security problems. On Windows, click the Windows icon, type Update, and open Windows Update. Click Check for updates. If updates are available, click Install now and restart when prompted. On Mac, click the Apple menu, go to System Settings, then General, then Software Update. Click Update Now if updates are available.

Drivers are software that control your hardware like your graphics card, network card, and sound card. Outdated drivers can cause slowness. On Windows, right-click the Windows icon, select Device Manager, and look for any devices with a yellow warning triangle. Right-click the device and select Update driver. On Mac, drivers usually update automatically with the operating system, so you do not need to do anything.

When to take your computer to a professional

If you have restarted, cleared space, closed background programs, run a malware scan, and disabled startup programs and your computer is still slow, the problem may be a failing hard drive, overheating, or a hardware issue. These require professional diagnosis. Contact a local computer repair shop, call your computer manufacturer's support line, or visit an authorized service center.

If your computer is more than five years old and still slow after these steps, it may be time to replace it. Older computers have slower processors and less memory than new ones, and no amount of cleaning will change that. A technician can tell you whether repair or replacement makes sense for your situation.

Frequently Asked Questions

How long does it take to see a speed improvement after these steps?

You should notice a difference when ready after restarting and closing background programs. Hard drive cleanup and malware scans take longer — a full scan can take an hour — but you will see results once they finish. If slowness returns within a few days, one of the problems is coming back, and you may need to repeat the steps or look for a new cause.

Is it safe to disable startup programs?

Yes, as long as you do not disable programs you actually use. Antivirus software, Windows Update, and security tools should stay enabled. Cloud storage apps, messaging programs, and games are safe to disable. If you disable something and your computer stops working the way you expect, you can re-enable it the same way.

What is the difference between a full scan and a quick scan in malware software?

A quick scan checks the most common places where malware hides and takes 5 to 10 minutes. A full scan checks every file on your hard drive and takes 30 minutes to an hour. If you suspect a serious infection or a quick scan found something, run a full scan. For routine maintenance, a quick scan is usually enough.

Can I speed up my computer by adding more RAM?

Yes, if your computer is using almost all its memory all the time. Check Activity Monitor on Mac or Task Manager on Windows to see your memory use. If it is consistently above 80 percent, adding RAM will help. However, this requires opening your computer or taking it to a technician, so try the free steps first.

Why does my computer slow down over time even though I do not install new programs?

Windows and Mac both create temporary files, cache, and logs that build up over time. Updates add files, and programs leave behind data even after you uninstall them. Malware and unwanted programs can also install themselves without your knowledge. Running the steps in this guide regularly — every few months — keeps your computer running at its best.