What actually slows a computer down, and what you can fix yourself

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 unwanted software, or a hard drive that is failing. You can fix the first three yourself in an hour or less. The fourth requires a replacement drive, which a repair shop can do for $100 to $300.

Before you do anything, restart your computer. This clears temporary files and stops programs that have frozen in the background. If the slowness stops after a restart, you are done. If it returns within a few days, one of the four causes above is the problem.

The fastest improvements come from removing startup programs and freeing up disk space. Both take 15 minutes and cost nothing. Malware removal takes longer but is worth doing if you have noticed new toolbars, pop-ups, or programs you did not install.

Key Takeaways

  • Restart your computer first — many slowness problems vanish after a reboot and do not return.
  • Disable startup programs through Task Manager (Windows) or Activity Monitor (Mac) to free up memory when you turn on your computer.
  • Delete old files, empty your Recycle Bin or Trash, and uninstall programs you no longer use to free up at least 10 percent of your hard drive space.
  • Run a malware scan with Malwarebytes or Windows Defender to catch unwanted software that slows performance.
  • If slowness persists after these steps, your hard drive may be failing and needs professional diagnosis.

Turn off programs that run when your computer starts

Every program set to launch at startup uses memory and processing power before you even open anything. Disabling the ones you do not need is one of the fastest ways to speed up your computer.

On Windows: Press Ctrl + Shift + Esc to open 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 — Spotify, Adobe Reader, Zoom, OneDrive, Dropbox — and select Disable. Leave Windows Defender, your antivirus, and your keyboard or mouse software enabled. Restart your computer for the change to take effect.

On Mac: Go to System Settings, then General, then Login Items. You will see a list of programs that open when you start your Mac. Click the minus sign next to any you want to remove. Restart your computer.

Most people can disable 5 to 10 programs without losing anything they need. The difference in startup time is usually noticeable within a week.

Free up space on your hard drive

When your hard drive is more than 85 percent full, your computer slows down because it has nowhere to write temporary files. Freeing up space is straightforward and costs nothing.

Check how much space you have: On Windows, right-click This PC and select Properties. Look for the bar labeled "Storage". On Mac, click the Apple menu, select About This Mac, then Storage. If the bar is mostly full or shows less than 20 GB free, you need to delete files.

What to delete: Start with Downloads folder — most people have gigabytes of installers and old files there. Delete anything you downloaded more than a month ago. Then empty your Recycle Bin (Windows) or Trash (Mac). Go to Control Panel > Programs > Programs and Features (Windows) or Applications folder (Mac) and uninstall software you no longer use. Video files, old backups, and duplicate photos take up the most space — if you have folders of these, move them to an external drive or cloud storage, then delete the originals.

Aim to free up at least 10 percent of your total drive space. On a 500 GB drive, that is 50 GB. On a 1 TB drive, that is 100 GB. The more space you free, the faster your computer will run.

Scan for malware and unwanted software

Malware, adware, and browser hijackers slow your computer by running in the background and consuming memory. They also cause pop-ups, new toolbars, and unexpected redirects. A malware scan takes 20 to 40 minutes and can recover significant speed.

Windows: Open Windows Defender (built into Windows 10 and 11). Click Virus & threat protection, then Scan options. Select Full scan and click Scan now. This scans your entire hard drive. When it finishes, it will show what it found. Let Windows Defender remove anything it detects. If you want a second opinion, read Malwarebytes (free version available) and run a scan there too.

Mac: macOS does not have a built-in malware scanner like Windows Defender. read Malwarebytes for Mac (free version available) and run a full scan. Mac is less commonly targeted by malware than Windows, but it is still worth checking if your computer is slow.

If a scan finds malware, remove it and restart your computer. Slowness from malware often improves when ready after removal.

Check your internet connection and browser

If your computer feels slow only when you are online, the problem is usually your browser or internet connection, not your computer itself.

First, restart your router. Unplug it for 30 seconds, plug it back in, and wait two minutes for it to fully restart. This fixes most internet slowness. If that does not help, run a speed test at speedtest.net to see what your actual internet speed is. If it is much slower than what your provider promised, contact them — you may have a line problem they can fix remotely.

If your internet speed is normal but your browser is slow, the problem is usually too many browser extensions or too much cache. In Chrome, Firefox, or Edge, go to Settings > Extensions and disable any you do not recognize or use regularly. Then go to Settings > Clear browsing data and select All time. Check Cookies and cached images, then click Clear data. Restart your browser.

Update your operating system and drivers

Operating system updates and driver updates often include performance improvements. Older versions of Windows or macOS can run slower than newer ones, and outdated graphics or network drivers can cause lag.

Windows: Go to Settings > Update & Security > Windows Update. Click Check for updates. If updates are available, install them and restart your computer. This usually takes 10 to 30 minutes.

Mac: Click the Apple menu, select System Settings, then General, then Software Update. If an update is available, click Update Now. Mac will restart automatically.

For drivers, Windows Update usually handles them automatically. If you have a graphics card from Nvidia or AMD, or a network adapter from Intel, you can visit their websites to read the latest drivers directly. Updating drivers is optional unless you are having specific problems with graphics or networking.

When to replace your hard drive

If you have done all the steps above and your computer is still slow, your hard drive may be failing. Hard drives typically last 3 to 5 years. Signs of failure include clicking or grinding sounds, freezing that happens randomly, or a blue screen error mentioning disk errors.

A failing hard drive cannot be fixed by software. You need a replacement, which costs $50 to $150 for the drive itself plus $100 to $200 for labor at a repair shop. If your computer is more than 5 years old, replacing the drive is usually worth it. If it is newer, a failing drive is often covered under warranty.

Before you replace a hard drive, back up your files. Use an external drive or cloud storage like Google Drive, OneDrive, or Dropbox. Once you have a backup, take your computer to a repair shop and ask them to replace the drive and reinstall Windows or macOS.

Frequently Asked Questions

Will adding more RAM speed up my computer?

Only if your computer is running out of memory. Open Task Manager (Windows) or Activity Monitor (Mac) and look at the Memory or RAM usage while you work. If it is consistently above 80 percent, adding RAM will help. If it is below 80 percent, more RAM will not make a noticeable difference. Disabling startup programs is usually cheaper and just as effective.

Should I use a cleaning software like CCleaner?

Cleaning software removes temporary files and registry entries, but Windows and Mac already do this automatically. CCleaner and similar tools rarely provide noticeable speed improvements and can sometimes cause problems if they remove files your system needs. The manual steps in this guide are safer and more effective.

Does defragmentation help on modern computers?

On older computers with traditional hard drives, defragmentation helped. On modern computers with solid-state drives (SSDs), defragmentation actually harms performance and should never be done. Windows and Mac handle file organization automatically on SSDs. If you are unsure whether you have an SSD, check your storage settings — SSDs are now standard on computers made after 2015.

What if my computer is still slow after I do all of this?

The problem is likely hardware failure — either a failing hard drive, failing RAM, or an overheating processor. Take your computer to a repair shop and ask them to run diagnostics. They can tell you which part is failing and what it will cost to replace. If your computer is more than 7 years old, replacement may be cheaper than repair.

Can I speed up my computer without restarting it?

Disabling startup programs and clearing browser cache will help without a restart, but you will see the full benefit only after you restart. A restart clears memory and stops background processes that have accumulated since your last startup. Restart your computer at least once a week to maintain speed.