What causes a computer to slow down and what you can do about 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 processor and memory that are straightforward overloaded. You can fix most of these yourself without paying for repairs or replacing the machine. The fastest wins come from stopping unnecessary startup programs, clearing disk space, and running a malware scan — in that order.

The steps below work on both Windows and Mac machines, though the exact menu names differ slightly. Start with the easiest fixes first, because they take minutes and often solve the problem completely.

Key Takeaways

  • Disable startup programs in your system settings to prevent them from running in the background when you turn on your computer.
  • Delete large files you no longer need and empty your recycle bin or trash to free up hard drive space.
  • Run a malware scan using Windows Defender (Windows) or Malwarebytes to check for viruses and unwanted software.
  • Close browser tabs and programs you are not actively using, since each one consumes memory and slows your machine.
  • If slowness persists after these steps, check your hard drive health or consider upgrading your RAM if your computer is more than five years old.

Stop programs from running when your computer starts

Many programs set themselves to launch automatically when you turn on your computer, even if you rarely use them. Each one takes memory and processor power, which slows everything down. You can see which programs are set to start and turn off the ones you do not need.

On Windows: Right-click the taskbar at the bottom of your screen and select "Task Manager." Click the "Startup" tab. You will see a list of programs with a "Status" column that says "Enabled" or "Disabled." Right-click any program you do not use regularly — such as Adobe Reader, Spotify, or Dropbox if you do not need it running all the time — and select "Disable." Restart your computer to see the change.

On Mac: Go to System Settings, then click "General" and select "Login Items." You will see a list of apps that open when you log in. Click the minus sign next to any app you want to remove. The change takes effect the next time you restart.

Free up hard drive space by deleting files and clearing cache

When your hard drive is more than 80 percent full, your computer slows down because it has no room to write temporary files. Check how much space you have left, then delete files you no longer need.

On Windows: Open File Explorer, right-click "This PC" on the left, and select "Properties." Look at the "Local Disk" bar — if the blue section takes up most of the bar, you are running low on space. Delete large files such as old video downloads, installer files, or duplicate photos. Then empty your Recycle Bin by right-clicking it on your desktop and selecting "Empty Recycle Bin."

On Mac: Click the Apple menu, select "About This Mac," then click "Storage." You will see a colored bar showing what is using space. Click "Manage" to see recommendations for files to delete, such as old downloads or large old files. Drag files you want to remove to the Trash, then empty the Trash by right-clicking it in the dock and selecting "Empty Trash."

You can also clear your web browser cache, which stores temporary files from websites you visit. In most browsers, press Ctrl+Shift+Delete (Windows) or Command+Shift+Delete (Mac), then select "All time" and click "Clear data." This usually frees up a few hundred megabytes.

Scan for malware and viruses

Malware and viruses run in the background and consume resources without your knowledge. A full scan takes 15 to 30 minutes but often reveals the cause of slowness.

On Windows: Open Windows Defender, which comes built into Windows. Click "Virus & threat protection," then click "Scan options." Select "Full scan" and click "Scan now." Windows will restart if it finds threats. This is normal and necessary.

On Mac: Mac does not include a built-in malware scanner like Windows Defender. read Malwarebytes for Mac (the free version works), install it, and run a full scan. If you prefer not to install additional software, you can use the built-in XProtect by restarting your Mac in Safe Mode — hold Shift while it starts — which runs a background scan automatically.

If a scan finds threats, follow the prompts to remove them. Do not ignore warnings about potentially unwanted programs, because these often cause slowness even if they are not technically viruses.

Close unused browser tabs and background programs

Each open tab in your web browser uses memory, and some websites run code that consumes processor power even when you are not looking at them. Closing tabs you are not actively using is one of the fastest ways to feel an when ready improvement.

Check your taskbar or dock for programs you have open but forgotten about — email clients, cloud storage apps, messaging programs, and media players all run in the background. Close the ones you are not using right now. You can always reopen them later.

If you find yourself with many tabs open regularly, consider using a tab manager extension in Chrome or Firefox that suspends inactive tabs automatically. These extensions pause tabs you have not clicked on in a set time, freeing up memory until you click back to them.

Restart your computer regularly

A restart clears your computer's memory and stops all background processes from accumulating. If you leave your computer on for weeks without restarting, slowness often builds up gradually. Restarting once a week or whenever you notice slowness is a straightforward habit that prevents many problems.

When you restart, wait for the computer to fully load before opening many programs at once. Launching 10 programs simultaneously will slow things down while they all load into memory.

Check your hard drive health if slowness persists

If you have completed all the steps above and your computer is still slow, your hard drive may be failing. A failing drive reads and writes data slowly, which affects everything you do.

On Windows: Open Command Prompt as an administrator (right-click it and select "Run as administrator"), then type wmic logicaldisk get name, size, freespace and press Enter. This shows your disk space. If you still have 20 percent or more free space and the slowness continues, run a disk check by typing chkdsk C: /f and pressing Enter. Windows will ask to schedule the check for the next restart. Allow it to run — this can take an hour but will identify and repair drive errors.

On Mac: Click the Apple menu, select "About This Mac," then click "Storage." If you have less than 10 percent free space even after deleting files, your drive is too full. If space is adequate, open Disk Utility (in Applications > Utilities), select your drive, and click "First Aid" to check for errors.

If a disk check finds many errors or if your computer is more than five years old and still slow after these steps, the hard drive may be near the end of its life. In that case, replacing it with a solid-state drive (SSD) is usually the best solution and will make your computer feel like new.

Consider upgrading RAM if your computer is older

Random Access Memory (RAM) is what your computer uses to run programs. If you regularly have many programs open and your computer slows to a crawl, you may not have enough RAM. Upgrading from 4 GB to 8 GB or 16 GB can make a noticeable difference, especially on computers that are five or more years old.

Check how much RAM you have: on Windows, right-click "This PC" and select "Properties"; on Mac, click the Apple menu and select "About This Mac." Look for "Installed RAM." If it says 4 GB or less and you often have slowness, upgrading is worth considering. RAM upgrades cost between $30 and $100 depending on your machine type and can be installed by a technician in 30 minutes, or by yourself if you are comfortable opening your computer.

Frequently Asked Questions

Why is my computer slow even though I have plenty of hard drive space?

Hard drive space is only one cause of slowness. If you have space available, the problem is likely too many startup programs, a malware infection, or insufficient RAM. Work through the startup programs and malware scan steps first, since those are free and take less than an hour. If slowness continues, check how much RAM you have and whether your hard drive is healthy using the disk check tools mentioned above.

Is it safe to disable all startup programs?

It is safe to disable most startup programs, but some are important. Never disable programs with names like "Windows Update," "Antivirus," or anything from your computer manufacturer. If you are unsure about a program, search its name online before disabling it. You can always re-enable a program later if you need it.

How often should I run a malware scan?

Run a full malware scan once a month as a preventive measure, or when ready if you notice sudden slowness, unexpected pop-ups, or programs you did not install. Windows Defender runs automatic scans in the background, so you do not need to do this manually unless you suspect a problem.

Will restarting my computer delete my files?

No. Restarting only stops programs and clears memory. All your files remain on your hard drive. Make sure to save any work you have open before restarting, just as you would before shutting down.

What should I do if my computer is still slow after trying all these steps?

If slowness persists, your hard drive may be failing or your RAM may be insufficient. Run the disk check tool described above to check for drive errors. If the drive is healthy and you have adequate space, upgrading your RAM or replacing your hard drive with an SSD are the most effective remaining options. A technician can diagnose the exact problem for $50 to $100 if you prefer not to troubleshoot further yourself.