Start with the fastest fixes first

A laggy computer usually comes from one of three things: too many programs running at once, a hard drive that is nearly full, or malware slowing things down. Before you reinstall Windows or buy new hardware, restart your computer, close programs you are not using, and check how much free space is left on your drive. Most of the time, one of these three steps will bring your speed back.

Lag feels different depending on what is causing it. If your mouse moves smoothly but programs take forever to open, your storage is probably full. If everything feels sluggish—clicking, typing, scrolling—something is running in the background and eating your processor. If your screen freezes for seconds at a time, you likely have malware or a failing hard drive. Knowing which one you have narrows down what to fix.

Key Takeaways

  • Restart your computer first—it closes background processes and clears temporary files that often cause lag without any other action needed.
  • Open Task Manager (Ctrl+Shift+Esc on Windows, Activity Monitor on Mac) to see which programs are using the most processor power and close the ones you do not need.
  • Check your free hard drive space by right-clicking your C: drive (Windows) or clicking the Apple menu and selecting About This Mac (Mac)—if you have less than 10 percent free, delete old files or uninstall programs.
  • Run a malware scan with Windows Defender (built into Windows) or a free tool like Malwarebytes to catch infections that slow your system down.
  • If lag persists after these steps, your hard drive may be failing or your RAM may be full, and you may need to replace hardware or take your computer to a technician.

Restart your computer and close unnecessary programs

The single fastest fix is a restart. When your computer runs for days or weeks without shutting down, temporary files pile up in memory, background processes multiply, and Windows itself gets bogged down. A restart clears all of that in two minutes. Shut down completely (not sleep mode), wait 30 seconds, and turn it back on.

While your computer restarts, think about what programs you actually need running. Every program that starts automatically when Windows boots—email clients, cloud storage, messaging apps, antivirus software—takes a slice of your processor and memory. Open Task Manager by pressing Ctrl+Shift+Esc on Windows. Look at the Processes tab and sort by CPU or Memory to see what is using the most power. Right-click anything you do not need running right now and select End Task. On a Mac, open Activity Monitor (search for it in Spotlight), click the CPU or Memory tab, and click the X button to quit programs you do not use.

Be careful not to close system processes—anything with "Windows" or "System" in the name should stay running. If you are unsure what something does, search its name online before closing it. After you close a few heavy programs, restart again and notice whether your computer feels faster.

Check your hard drive space and delete unnecessary files

When your hard drive is more than 90 percent full, Windows slows down dramatically because it cannot write temporary files or cache data efficiently. On Windows, right-click your C: drive in File Explorer and select Properties. Look at the pie chart—if the blue section (used space) takes up most of the circle, you need to free up room. On a Mac, click the Apple menu, select About This Mac, and click Storage to see how much space is left.

Start by deleting files you genuinely do not need. Empty your Downloads folder—it often holds installers and files from months ago. Go to your Documents, Pictures, and Desktop folders and move old files to an external drive or cloud storage, then delete them from your computer. Uninstall programs you no longer use by going to Settings > Apps > Apps & Features on Windows, or Applications folder on Mac, and removing them.

If you still do not have at least 10 percent free space, use Disk Cleanup on Windows (search for it in the Start menu) to remove temporary files, old Windows updates, and cache. On a Mac, empty the Trash by right-clicking it and selecting Empty Trash. After freeing up space, restart your computer and test whether programs open faster.

Scan for malware and viruses

Malware—including viruses, spyware, and adware—often runs silently in the background and consumes processor power and bandwidth. If your computer is slow but your hard drive has space and few programs are running, malware is a likely culprit. Windows comes with Windows Defender built in, which is free and effective for most infections. 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 but checks every file on your drive.

If Windows Defender finds nothing but your computer is still slow, read Malwarebytes (the free version is sufficient) from malwarebytes.com. Install it, open the program, and click Scan. Malwarebytes is particularly good at catching adware and browser hijackers that Windows Defender sometimes misses. If either scan finds threats, let the program remove them and restart your computer.

After running a malware scan, check your browser extensions and startup programs. Open your browser settings and look at installed extensions—remove any you do not recognize or use. On Windows, open Task Scheduler and look at the Startup tab to see what programs launch when you boot; disable anything unnecessary. These are common places malware hides.

Update Windows and your drivers

Outdated Windows versions and drivers (the software that controls your hardware) can cause lag and compatibility problems. On Windows, go to Settings > Update & Security > Windows Update and click Check for Updates. Install any available updates and restart. On a Mac, click the Apple menu, select System Settings, and go to General > Software Update.

Drivers for your graphics card, network adapter, and chipset sometimes have bugs that slow your system. On Windows, right-click the Start menu, select Device Manager, and look for any devices with a yellow warning triangle. Right-click those devices and select Update Driver. If you have an NVIDIA or AMD graphics card, visit their websites directly to read the latest driver. On a Mac, drivers usually update automatically through Software Update, so you do not need to do anything extra.

Check your RAM and consider a hardware upgrade

If your computer is still slow after restarting, freeing space, closing programs, and scanning for malware, your RAM (memory) may be full or your hard drive may be failing. Open Task Manager on Windows and look at the Memory column—if it shows 90 percent or higher consistently, you do not have enough RAM for what you are doing. On a Mac, open Activity Monitor, click the Memory tab, and look at the Memory Pressure graph at the bottom; if it is yellow or red, your RAM is maxed out.

Adding more RAM is the most cost-effective upgrade for a slow computer. If you have 4 GB or less, upgrading to 8 GB or 16 GB will make a noticeable difference. However, this requires opening your computer, and if you are not comfortable doing that, a technician can install it for $50 to $100 in labor. Alternatively, if your computer is more than five years old and still has a traditional hard drive (not a solid-state drive), replacing it with an SSD will make the biggest speed improvement you can get.

If you are not sure whether your computer has an SSD or a traditional hard drive, open Disk Management on Windows (search for it in the Start menu) and look at your C: drive—if it says SSD, you have one. On a Mac, click the Apple menu, select About This Mac, click Storage, and look at the drive type. If you have a traditional hard drive and your computer is slow even after these fixes, replacing it with an SSD is worth the investment.

Disable visual effects and background services

Windows and Mac both include visual effects—animations, transparency, shadows—that look nice but use processor power. If your computer is older or has limited RAM, turning these off can help. On Windows, right-click This PC or My Computer, select Properties, click Advanced System Settings, and go to the Advanced tab. Under Performance, click Settings and select Adjust for Best Performance. This disables most animations and visual effects. On a Mac, go to System Settings > Accessibility > Display and enable Reduce Motion and Reduce Transparency.

You can also disable background services that run even when you are not using them. On Windows, press Windows+R, type services.msc, and look through the list. Services like Windows Update, Superfetch, and Search Indexer can be set to Manual or Disabled if you do not need them running constantly. Be cautious—only disable services you recognize and are sure you do not need. On a Mac, go to System Settings > General > Login Items and remove programs you do not want starting automatically.

Frequently Asked Questions

Why is my computer slow only when I open certain programs?

That program is probably using a lot of processor power or RAM. Open Task Manager while the program is running and check the CPU and Memory columns to confirm. If one program consistently uses 50 percent or more of your processor, it may have a bug, or your computer may not have enough power for it. Try closing other programs first, updating the problematic program, or reinstalling it.

Does clearing my browser cache and cookies help speed up my computer?

It helps a little, but not much. Clearing your browser cache frees up a small amount of hard drive space and can make your browser load pages slightly faster. Go to your browser settings, find Privacy or History, and select Clear Browsing Data. However, this is a minor fix compared to restarting, closing background programs, or freeing up hard drive space.

Is it safe to disable Windows Update to speed up my computer?

No. Windows Update patches security vulnerabilities and fixes bugs. Disabling it leaves your computer exposed to malware and hackers. If updates are slowing you down, the problem is usually that your hard drive is full or your RAM is maxed out, not the updates themselves. Fix those issues instead of disabling updates.

What is the difference between restarting and shutting down?

Restarting shuts down your computer completely and turns it back on, which clears memory and closes all background processes. Sleep mode keeps your computer in a low-power state but does not clear memory or close programs. Always use a full restart when your computer is slow—sleep mode will not fix the problem.

Should I defragment my hard drive to speed it up?

Only if you have a traditional hard drive, not an SSD. Defragmentation reorganizes files on a mechanical drive so they are read faster. On Windows, search for Defragment and Optimize Drives and run it. On a Mac, defragmentation is not necessary. If you have an SSD, defragmentation can actually shorten its lifespan, so skip it entirely.