What slows down a computer and how to fix it

A slow computer usually comes from one of four things: too many programs running at startup, a hard drive that is nearly full, malware or viruses, or a hard drive that is failing. You can check and fix the first three yourself in under an hour. The fourth requires replacing the drive.

Start by restarting your computer—this clears temporary files and stops programs that are stuck in memory. If the computer is still slow after a restart, move through the fixes below in order. Most people find their speed returns after disabling startup programs or freeing up disk space.

Key Takeaways

  • Restart your computer first, then check how much free space is left on your hard drive—if it is below 15 percent of total capacity, delete or move files to free up room.
  • Open Task Manager (Windows) or Activity Monitor (Mac) to see which programs are using the most CPU and memory, and close the ones you do not need running right now.
  • Disable programs that start automatically when you turn on your computer by going to Settings > Apps > Startup and toggling off anything you do not use daily.
  • Run a malware scan using Windows Defender (built into Windows) or a free tool like Malwarebytes to check for viruses or unwanted software slowing your system.
  • If your computer is still slow after these steps, the hard drive may be failing and will need to be replaced by a technician.

Check how much disk space you have left

A hard drive that is more than 85 percent full will slow down noticeably because the operating system cannot write temporary files. On Windows, right-click the C: drive in File Explorer, select Properties, and look at the pie chart. On Mac, click the Apple menu, select About This Mac, then Storage. If your free space is less than 15 percent of the total, you need to delete or move files.

Start by emptying the Recycle Bin (Windows) or Trash (Mac)—deleted files sit there until you empty it, still taking up space. Then look for large files you no longer need: old video files, installation files for programs you have already installed, or duplicate photos. Use a tool like WinDirStat (Windows, free) or Disk Diag (Mac, free) to see which folders are taking up the most space.

If you have less than 5 gigabytes free, consider moving large files to an external hard drive or cloud storage like Google Drive or OneDrive. This frees up space without deleting anything permanently.

Turn off programs that start when you boot up

Many programs set themselves to launch automatically when you turn on your computer, and each one uses memory and processing power even if you are not using it. On Windows 10 or 11, right-click the taskbar at the bottom of the screen, select Task Manager, then click the Startup tab. You will see a list of programs with a Status column showing Enabled or Disabled.

Look for programs you do not use every day—things like Adobe Reader, Spotify, Dropbox, or messaging apps. Right-click each one and select Disable. Leave antivirus software and Windows Update enabled. On Mac, go to System Settings > General > Login Items, then click the minus sign next to any program you want to remove from startup.

Restart your computer after making changes. You will notice the boot time is faster, and the computer will be more responsive while you work because memory is not being used by background programs.

Close programs using too much memory or CPU

Even after disabling startup programs, some applications running right now may be using more resources than they should. Open Task Manager on Windows by pressing Ctrl + Shift + Esc, or on Mac open Activity Monitor by pressing Command + Space, typing "Activity Monitor," and pressing Enter.

On Windows, click the Memory column header to sort by memory use, highest first. On Mac, click the Memory tab and look at the Mem column. Programs at the top are using the most. If you see something using more than 50 percent of your available memory and you are not actively using it, close it. Right-click the program name and select End Task (Windows) or click it and press the X button (Mac).

Common culprits are web browsers with many tabs open, video editing software, or games. Closing them will free up memory when ready. If the same program keeps using excessive resources, it may have a bug—try uninstalling and reinstalling it, or look for an updated version.

Scan for malware and viruses

Malware and viruses run in the background and consume processing power and bandwidth, making your computer feel sluggish. Windows comes with Windows Defender built in. Open Settings, go to Privacy & Security > Virus & Threat Protection, and click Scan Options. Select Full Scan and click Scan Now. A full scan takes 30 minutes to an hour.

If you prefer a second opinion, read Malwarebytes (free version available) from malwarebytes.com. Install it, open the program, and click Scan. Malwarebytes is particularly good at finding unwanted toolbars, browser hijackers, and other programs that slow down web browsing.

After the scan finishes, Malwarebytes will show you what it found. Click Remove to delete detected threats. Restart your computer when prompted. If malware was present, you should notice an when ready improvement in speed.

Update Windows or macOS and your drivers

Operating system updates often include performance improvements and security patches that prevent malware from slowing your system. On Windows, go to Settings > Update & Security > Windows Update and click Check for Updates. Install any available updates and restart. On Mac, go to System Settings > General > Software Update and install any updates shown.

Outdated drivers—the software that lets Windows or macOS communicate with your hardware—can also cause slowdowns. On Windows, right-click the Start button, select Device Manager, and look for any devices with a yellow exclamation mark. Right-click those devices and select Update Driver. On Mac, drivers usually update automatically with the operating system.

When to replace your hard drive

If you have completed all the steps above and your computer is still slow, the hard drive itself may be failing. Hard drives typically last 3 to 5 years. Signs of failure include clicking or grinding noises, files taking a very long time to open, or the computer freezing for 10 to 30 seconds at a time.

You can check hard drive health on Windows using a free tool like CrystalDiskInfo—read it, install it, and it will show you the drive's status. On Mac, Disk Utility (in Applications > Utilities) can run a verification. If either tool reports errors or a failing status, the drive needs to be replaced. This is a job for a computer repair technician, as it involves opening the computer and transferring your data to a new drive.

Before taking it to a technician, back up your important files to an external drive or cloud storage. Once the new drive is installed, your computer will be noticeably faster.

Frequently Asked Questions

How long should a full malware scan take?

A full scan with Windows Defender or Malwarebytes usually takes 30 minutes to an hour, depending on how many files are on your computer. You can continue using your computer while the scan runs, though it will be slower. Let it finish completely before restarting.

Is it safe to disable all startup programs?

No. Leave antivirus software, Windows Update, and any security tools enabled. Disable only programs you recognize and do not use daily, like Spotify, Adobe Reader, or messaging apps. If you are unsure what a program does, search its name online before disabling it.

What if my computer is still slow after I free up disk space?

Move to the next step: check Task Manager or Activity Monitor to see if a program is using too much memory, then run a malware scan. If all three steps are complete and the computer is still slow, the hard drive may be failing and will need replacement.

Can I speed up my computer by adding more RAM?

Adding RAM helps if Task Manager or Activity Monitor shows your memory is constantly above 80 percent. However, most slowdowns come from disk space, startup programs, or malware, not lack of RAM. Try the free fixes first. If you still have problems after that, a technician can check whether more RAM would help.

Should I use a cleaning tool to speed up my computer?

Most paid "cleaning" tools do not improve speed and some are malware themselves. Stick to the built-in tools: Task Manager (Windows), Activity Monitor (Mac), Disk Cleanup (Windows), and Windows Defender. These are free and safe.