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A computer that has become slow is frustrating, but it is rarely mysterious. The cause is nearly always one of a handful of things. Work through them in order, because the early ones are free.
1. Restart it properly
It sounds too simple, but many computers are never truly restarted, only put to sleep. Choose Restart, not Shut down. On Windows a restart clears more than a shut down does, because of a feature called Fast Startup. If it has been weeks since the last restart, this alone can help.
2. See what is running
On Windows, press Ctrl + Shift + Esc to open Task Manager and look at the Processes tab. On a Mac, open Activity Monitor.
Click the CPU and Memory columns to sort by them. If one program is using most of either, you have found the problem. A web browser with dozens of tabs open is the usual suspect. Close what you do not need.
3. Trim the start-up list
Many programs set themselves to launch when the computer starts, and then sit in the background for the rest of the day.
- Windows: Task Manager, then the Startup apps tab. Disable anything you do not need the moment the computer starts. This does not uninstall anything.
- Mac: System Settings, then General, then Login Items.
4. Check the free space
A drive that is nearly full slows everything down, and updates start to fail. Try to keep at least 15 to 20 percent free.
Empty the recycle bin, clear the Downloads folder, and uninstall programs you no longer use. Windows has a built-in cleanup tool under Settings, System, Storage.
5. Scan for malware
Unwanted software slows a computer and puts your information at risk. Run a full scan with the security software you already have. Windows Security is built in and is good.
Signs that point to malware: new toolbars, a changed home page or search engine, pop-ups when no browser is open, or a fan that runs hard when you are doing nothing.
6. Let the updates finish
A computer that is halfway through a large update can be slow for an hour or more. Check Windows Update, or Software Update on a Mac, let it finish, and restart. Staying up to date also fixes performance and security problems over time.
7. Look at the hardware
If the free fixes did not help, two inexpensive upgrades make the biggest difference.
Replace a hard drive with an SSD. If the computer has an old-style spinning hard drive, this is the best upgrade you can buy. Start-up falls from minutes to seconds and everything feels faster. To check on Windows, open Task Manager, go to the Performance tab and select the disk. It will say HDD or SSD.
Add memory. 4 GB is not enough for current software. 8 GB is a workable minimum and 16 GB is comfortable. On many laptops the memory can be upgraded, but on some it is fixed to the main board and cannot be changed.
When it is not worth it
If the computer is more than seven or eight years old, or it cannot run a version of Windows or macOS that still gets security updates, money spent on upgrades is usually better put toward a replacement.
A warning about speed-up software
Avoid programs that promise to clean, optimize or speed up your PC, especially ones that arrive as pop-up adverts. At best they do what the built-in tools already do. At worst they are the cause of the problem.