Step 1: find the bottleneck
Every slow computer is slow because one specific resource is saturated. Find out which.
Windows
Press Ctrl + Shift + Esc to open Task Manager, and go to the Performance tab. You'll see live graphs for CPU, Memory, Disk, and GPU. Use the machine normally for a minute while it's open — open the app that feels slow — and watch which graph goes to the top and stays there.
Then switch to the Processes tab and click a column heading to sort by that resource. Whatever is at the top of the saturated column is your suspect.
macOS
Open Activity Monitor (Applications → Utilities, or press Command + Space and type it). The tabs across the top — CPU, Memory, Energy, Disk, Network — do the same job. On the Memory tab, the number that matters is Memory Pressure at the bottom: green is fine, yellow means you're compressing and swapping, red means you're short of RAM.
Disk near 100% → you're waiting on storage. Very common on older machines with a spinning hard drive.
Memory near full / pressure yellow-red → not enough RAM for what you're running.
CPU near 100% with an identifiable process → one program, or malware.
Everything low, machine still slow → likely heat, power settings, or a network wait.
If the disk is at 100%
This is the most common cause of a laptop that was fine three years ago and is now unusable — and the most fixable.
Find out what kind of drive you have
On Windows, open Task Manager → Performance → Disk; the panel names the drive type. Or open Defragment and Optimise Drives from the Start menu: it lists each drive's media type as either "Hard disk drive" or "Solid state drive".
If it says hard disk drive, that is very likely your whole problem. A mechanical drive can service only a few hundred operations per second; an SSD handles tens of thousands. Modern operating systems and browsers assume the latter. Replacing a hard drive with an SSD is the single largest performance improvement available on an old laptop — bigger than doubling the RAM, bigger than a faster processor, and usually inexpensive. A machine that takes three minutes to reach a usable desktop will do it in fifteen seconds.
If you already have an SSD and it's still pegged
- Check free space. SSDs need spare room to manage writes. Once a drive is above roughly 90% full, performance falls off noticeably. Aim to keep at least 10–15% free.
- Look at what's writing. Sort Task Manager's Processes by Disk. Frequent offenders: a cloud storage client re-syncing, an antivirus full scan, Windows Update installing in the background, or a search indexer rebuilding after an update. Most of these are temporary — the correct response to "Windows Update is using the disk" is to let it finish, ideally by leaving the machine on and plugged in for an hour.
- Two antivirus programs. If a third-party antivirus is installed alongside the built-in one, they can scan each other's activity in a loop. Keep one.
If memory is full
When RAM runs out, the system moves data to disk to compensate. That's dramatically slower, and it's why a machine short of memory feels like it's wading through treacle rather than simply running slowly.
- Find the consumer. Sort by Memory. In most cases the top entry is a browser, and the reason is tab count plus extensions.
- Restarting helps and it isn't a joke. Memory leaks in long-running apps are real. If you haven't rebooted in three weeks, do that before anything else.
- Consider adding RAM. On laptops with accessible memory slots this is cheap and effective. On many modern thin laptops — and all Apple Silicon Macs — memory is soldered and cannot be changed, so this is a decision you make when buying, not later. Check your specific model before ordering anything.
- Work within what you have. If you can't add RAM: fewer simultaneous tabs, close the apps you're not using, and turn off browser extensions you don't need.
If the CPU is pinned
Sort by CPU and look at the top process. Three broad categories:
Something that's supposed to be busy
A video export, a game, a large file compression, an operating system update. Nothing is wrong; wait for it. Windows Update and macOS updates in particular can consume a machine for an extended period after a major release, and interrupting them repeatedly makes it worse.
Something misbehaving
An app at 100% CPU while apparently doing nothing is stuck. Quit and reopen it. If it recurs, update or reinstall it. A single crashing background helper that restarts every few seconds can hold a machine down indefinitely.
Something you didn't install
A process you don't recognise using constant CPU, particularly with a generic name and an unfamiliar location, deserves scrutiny. Search the exact process name before doing anything drastic — plenty of legitimate system components have odd names.
Run a scan with the built-in security tool (Windows Security on Windows; on Mac, a scan from a reputable vendor). Then check what launches at startup and what browser extensions are installed, because that's where unwanted software usually hides. Note that many "your PC is infected, download our cleaner" pages are themselves the problem — never install security software from a pop-up.
If it starts fast and then gets slow — thermal throttling
A distinctive pattern: the laptop is responsive for the first ten minutes, then progressively degrades, and the fan is loud throughout. That's the processor reducing its own clock speed to stay within a safe temperature.
Causes, in order of likelihood:
- Blocked vents. Using a laptop on a bed, sofa, or lap blocks the intake underneath. A hard flat surface, or a simple stand, can be the entire fix.
- Dust. After a few years the heatsink fins clog with a felt of dust. Compressed air through the vents helps; a proper clean means opening the case, which is straightforward on some models and not on others.
- Old thermal paste. On laptops more than about five years old the paste between chip and heatsink dries out. Replacing it is a real repair, but a competent shop does it cheaply and the improvement can be dramatic.
- Power profile. On Windows, check Settings → System → Power & battery and make sure you're not in a power-saving mode while plugged in. Some manufacturers also ship their own control app with "quiet" and "performance" modes that override the Windows setting.
If it's slow to start up
Boot time is largely determined by how many programs insist on launching with the system.
- Windows: Task Manager → Startup apps. It lists each item with a "Startup impact" rating. Disable anything rated High that you don't need immediately at login — updaters, launchers for apps you open occasionally, cloud clients you can start manually. Disabling here doesn't uninstall anything; the app still works when you open it.
- macOS: System Settings → General → Login Items. Remove what you don't need from both the "Open at Login" list and the background items list below it.
Also worth doing once: uninstall software you genuinely no longer use. Not for the disk space — for the background services and updaters that come with it.
If it's only slow in the browser
Very often "my laptop is slow" means "the web is slow on my laptop", which is a different and easier problem.
- Test in a private window. Extensions are disabled there by default. If the browser is suddenly quick, an extension is your culprit — re-enable them one at a time to find which.
- Count your tabs. Each one holds memory. Most browsers now sleep inactive tabs; make sure that setting is on.
- Use the browser's own task manager. Chrome and Edge have one (Shift + Esc on Windows) that shows resource use per tab and per extension. It will name the offending tab in seconds.
- Update the browser and restart it fully. Browsers accumulate memory over long sessions.
- If pages are slow to start loading rather than slow to render, the problem is the network rather than the machine — see our Wi-Fi guide.
When it really is time to upgrade
Not every slow laptop is salvageable. Consider replacement when:
- It already has an SSD, adequate RAM, and clean vents, and it's still slow at ordinary tasks.
- It no longer receives security updates. This matters more than speed.
- The cost of the repairs it needs approaches a meaningful fraction of a replacement.
But do the SSD and RAM check first. A very large number of laptops that get replaced as "too slow" needed a drive that costs a fraction of a new machine.
Registry cleaners deliver no measurable speed benefit on modern Windows and can break things. All-in-one "optimisers" mostly run the same maintenance the OS already runs on a schedule, wrapped in a subscription. Defragmenting an SSD is unnecessary and adds wear — Windows already handles SSDs correctly on its own.