"It's gotten slow" is one of the vaguest things a computer can do, which is why it usually gets the vaguest advice back. In practice there are only a handful of real causes, and most of them are cheap to fix. The expensive one is a spinning hard drive, and it's also the most common.
A spinning hard drive, not an SSD
If the laptop is more than five or six years old and nobody has ever mentioned upgrading it, there's a good chance it's still running the mechanical hard drive it shipped with. Those get slower with age and were never fast to begin with compared to solid state storage. This is the single biggest cause of "it used to be fine and now it's unbearable."
The other three causes
Too many programs starting with Windows, each one eating memory and CPU before you've opened anything yourself. A drive that's almost completely full, which slows Windows down in ways that have nothing to do with the drive's speed. And malware running quietly in the background, which is worth ruling out properly rather than guessing, see our virus and malware removal page.
What we actually check
-
Drive type and health
HDD or SSD, and whether the drive itself is showing early warning signs.
-
Startup programs
What's loading automatically, and how much of it you actually use.
-
Malware scan
Ruling it out properly rather than assuming.
-
Memory and storage space
Whether the machine simply doesn't have enough of either for how it's used.
Common questions
Will an SSD really make that much difference?
On a machine with a spinning hard drive, it's usually the single biggest improvement available. Boot times that were a minute or more often drop to fifteen seconds.
Is it worth doing on an old laptop?
Depends on the rest of the machine. A slow hard drive on an otherwise capable laptop is worth fixing. A slow hard drive on a laptop that's also underpowered everywhere else usually isn't, and we'll say so.
Could it just be too many browser tabs?
Genuinely, sometimes yes. If it's only slow with Chrome open and forty tabs stacked up, that's a habit, not a fault, and we'll tell you that too rather than sell you a repair you don't need.
How long does the cleanup take?
Usually one to two hours at $150 per hour. An SSD swap and full data transfer takes longer and we'll quote it separately once we know the drive is the cause.