The most common reasons your computer slows down
A slow computer usually comes from one of five things: too many programs running at once, a hard drive that is nearly full, malware or viruses, an overheating processor, or a failing hard drive. Most of the time it is the first two. Your computer has limited memory (RAM) and storage space, and when both are stretched thin, everything takes longer—opening files, switching between programs, even just moving your mouse across the screen.
The second most common culprit is background programs you did not know were running. Windows and Mac both start dozens of services and applications automatically when you turn on your computer. Some are necessary; many are not. Each one uses a small amount of your processor and memory, and together they add up fast.
Less common but more serious are hardware problems. A hard drive that is failing will slow your computer to a crawl as it struggles to read and write files. Overheating can also throttle your processor—your computer deliberately slows itself down to avoid damage when the CPU temperature climbs too high.
Key Takeaways
- Check how much free space you have on your hard drive; if it is below 10 percent of total capacity, clearing files or uninstalling programs will usually speed things up noticeably.
- Open your Task Manager (Windows) or Activity Monitor (Mac) to see which programs are using the most memory and processor power, then close or uninstall the ones you do not use.
- Malware and viruses can slow your computer significantly, so run a full scan with your antivirus software if you have not done so recently.
- If your computer is hot to the touch or the fan is running constantly, dust buildup inside the case may be blocking airflow; cleaning the vents and fans can restore speed.
- A hard drive that is making clicking or grinding sounds, or one that causes frequent freezing, may be failing and should be backed up when ready.
How to check what is using your memory and processor
The fastest way to find the culprit is to open your system monitor. On Windows, right-click the taskbar at the bottom of your screen and select Task Manager. On Mac, open Spotlight (Command + Space), type Activity Monitor, and press Enter. Both tools show you every program running and how much memory and processor power each one is using.
Look at the columns labeled Memory and CPU (or %CPU on Mac). Programs at the top of the list are using the most resources. If you see something you do not recognize or do not use, you can close it by selecting it and clicking End Task (Windows) or the X button (Mac). Closing a program does not uninstall it—it just stops it from running right now.
If the same program keeps appearing at the top and you do not use it, uninstall it entirely. On Windows, go to Settings > Apps > Apps & features, find the program, and click Uninstall. On Mac, open Applications in Finder, drag the program to the Trash, and empty the Trash.
Checking your hard drive space
A hard drive that is more than 90 percent full will slow your computer down because the operating system needs free space to write temporary files and swap memory. To check how much space you have left, right-click your main drive (usually C: on Windows or Macintosh HD on Mac) and select Properties (Windows) or Get Info (Mac).
If you have less than 10 percent free space, you need to delete files or uninstall programs. Start by emptying your Downloads folder and your Recycle Bin (Windows) or Trash (Mac)—these often hold gigabytes of files you no longer need. Then look for large files you can delete: old videos, archived photos, or installation files for programs you no longer use.
If you are still short on space, uninstall programs you rarely use. On Windows, go to Settings > Apps > Apps & features. On Mac, open Applications in Finder. Look for anything you have not opened in months and remove it. Uninstalling even a few large programs can free up 10 to 50 gigabytes.
Malware and viruses as a cause of slowness
Malware and viruses can consume processor power and memory without your knowledge, or they can corrupt files so your computer has to work harder to read them. If you have not run a full antivirus scan recently, do that now. Most Windows computers come with Windows Defender built in; on Mac, the built-in protection is called XProtect.
To run a full scan in Windows Defender, click the Windows icon, type Windows Security, and open it. Select Virus & threat protection, then Scan options, choose Full scan, and click Scan now. A full scan can take an hour or more, so start it when you do not need your computer. On Mac, open System Settings > General > Security & Privacy and check the status of XProtect.
If you suspect malware beyond what your built-in antivirus catches, consider running a second opinion scan with a tool like Malwarebytes. This is free to read and use for a single scan, though it will prompt you to buy a subscription for ongoing protection. Do not pay for it unless you want continuous monitoring.
Overheating and dust buildup
If your computer is hot to the touch, the fan is running constantly, or you hear loud whirring sounds, overheating is likely slowing you down. Your processor automatically reduces its speed when it gets too hot to protect itself from damage. Dust buildup inside the case blocks airflow and traps heat.
The easiest fix is to clean the vents and fan openings. Use a can of compressed air (available at any office supply store) and blow short bursts into the vents on the sides and back of your computer. Do this outdoors or in a well-ventilated area, because dust will fly everywhere. Hold the can upright and use short bursts—do not shake it or tilt it, or liquid will spray out.
If you are comfortable opening your computer case, you can clean the internal fans and heatsinks more thoroughly. Unplug the computer first, then remove the side panel (usually held by two or three screws). Use compressed air to blow dust off the fans and the large metal fins attached to the processor. If you are not comfortable doing this, a computer repair shop can do it for $30 to $75.
Signs your hard drive is failing
A hard drive that is failing will cause slowness that no amount of cleaning or uninstalling will fix. Listen for clicking, grinding, or beeping sounds coming from inside your computer—these are warning signs. You might also notice that your computer freezes for 10 to 30 seconds at a time, or that files take a very long time to open or save.
If you suspect a failing hard drive, back up your data when ready. Copy your important files to an external hard drive, a USB flash drive, or a cloud service like OneDrive, Google Drive, or iCloud. Do not wait—a failing drive can stop working completely without warning, and recovery is expensive.
Once your data is backed up, you should have the drive replaced. This is not a do-it-yourself job unless you are experienced with computer hardware. A repair shop can replace a hard drive for $100 to $300 in labor, plus the cost of the new drive itself. If your computer is old, it may be worth considering a replacement instead.
Startup programs that run automatically
Many programs are set to start automatically when you turn on your computer, even if you do not use them. Each one adds a few seconds to your startup time and uses memory while your computer is running. Disabling the ones you do not need can make a noticeable difference.
On Windows, open Task Manager (right-click the taskbar and select Task Manager, or press Ctrl + Shift + Esc). Click the Startup tab. You will see a list of programs that start automatically. Right-click any program you do not need and select Disable. Be careful not to disable anything you are unsure about—if you disable something important, you can always re-enable it later.
On Mac, go to System Settings > General > Login Items. You will see a list of programs that open when you log in. Select any you do not need and click the minus button to remove them. This does not uninstall the program; it just stops it from starting automatically.
When to call a professional
If you have tried the steps above and your computer is still slow, or if you hear clicking sounds from inside the case, it is time to take it to a repair shop. A technician can run diagnostics to check the health of your hard drive, test your RAM, and look for hardware problems you cannot see. Diagnostics usually cost $50 to $100 and can tell you whether a repair is worth the cost.
If your computer is more than five years old and a major repair is needed, compare the repair cost to the price of a new computer. Sometimes replacement is the better choice. If your computer is newer and the repair is straightforward—like replacing a hard drive or adding more RAM—it is usually worth fixing.
Frequently Asked Questions
Why is my computer slow only when I open certain programs?
That program is using a lot of memory or processor power. Open Task Manager or Activity Monitor while the program is running and check how much it is using. If it is using more than 50 percent of your CPU or most of your available RAM, the program itself may be poorly designed, or your computer may not have enough memory to run it smoothly. You can either close other programs before opening it, or upgrade your RAM if you use that program often.
Does restarting my computer actually help?
Yes, but only temporarily. Restarting clears your RAM and stops all running programs, which can make your computer feel faster for a while. However, if the underlying problem is a full hard drive, malware, or a failing drive, the slowness will return. Restart as a first troubleshooting step, but if slowness comes back within hours, investigate the causes listed above.
Is it safe to uninstall programs I do not recognize?
Usually yes, but be cautious. If you do not recognize a program, search for its name online before uninstalling it—you may find that it is part of another program you do use. Avoid uninstalling anything with "Windows" or "Microsoft" in the name, or anything related to your antivirus software. When in doubt, disable it from startup instead of uninstalling it; if nothing breaks, you can uninstall it later.
Can too many browser tabs slow down my computer?
Yes. Each open tab uses memory, and if you have 20 or 30 tabs open, your browser can use several gigabytes of RAM. Close tabs you are not actively using, or use a tab manager extension that suspends inactive tabs. If you regularly keep many tabs open, adding more RAM to your computer will help.
What is the difference between a slow computer and a slow internet connection?
A slow computer affects everything—opening files, switching programs, even moving your mouse. A slow internet connection affects only things that need the internet, like loading web pages or downloading files. To tell the difference, open a program that does not need the internet (like Notepad or Word) and see if it opens quickly. If it does, your internet is the problem, not your computer.