Why does my laptop slow down when it gets hot?

A laptop is a small box asked to shift a surprising amount of heat through a slot the width of a pencil. Everything about how it performs under load follows from how well that works on a given day. Understanding the path makes the symptoms legible: a loud fan means the machine is trying, and a slow machine with a loud fan means it is trying and losing.

Step by step

1. Follow the heat path once, so the symptoms make sense.Chip under the keyboard, flat copper pipe carrying heat sideways, a small radiator of thin metal fins near the hinge, a fan pulling air in through the underside and pushing it out through a slot at the back or side. Every stage has to be open.
2. Understand what the machine does when it cannot cope.It reduces the processor's speed and voltage in steps until the temperature is safe. Nothing breaks; the machine simply becomes slower under load while staying perfectly responsive for light work. That asymmetry is the signature.
3. Check the surface first.The intake vents are millimetres from whatever the laptop stands on. A duvet, a cushion, a lap or a thick rug seals them completely. A hard flat surface, or anything that lifts the base a centimetre, restores the airflow immediately.
4. Consider the age and the dust.Dust does not settle evenly; it packs into a felt-like mat across the face of the fins where the air enters them. A machine two or three years old can be substantially blocked while looking spotless from outside.
5. Find out whether software is the cause.Open the task manager or activity monitor and look at what is using the processor when the fan is loud. A stuck background process, a browser tab, an indexing job after an update, or a sync client working through a large folder are all common and all fixable without touching hardware.
6. Separate normal from abnormal.Hot and loud during video editing, gaming or a long export is the machine working correctly. Hot and loud while idle means software. Hot, loud and slow on a hard desk with nothing running means the cooling path.
7. Reduce the demand where you can.Fewer browser tabs, closing what is not in use, and using a power mode that favours efficiency over speed all lower the heat produced. On a warm day that alone can keep a machine out of throttling.
8. Get it cleaned properly rather than blowing air into it.Compressed air aimed into a vent drives dust deeper into the fins and can spin the fan beyond its rated speed. A proper clean means opening the machine, which is a repair-shop job with the machine off, unplugged and the battery isolated.
9. Know when it is the thermal paste.On a machine many years old, the compound between the chip and the heat pipe dries out and conducts less well. Replacing it restores performance noticeably, and it is a workshop job rather than a householder one.

Tips

• A simple stand that lifts the back of the laptop a couple of centimetres helps more than most cooling pads, because it opens the intake rather than blowing air at the underside.
• If the machine is hot but the fan is quiet, check whether a silent or quiet fan profile has been selected in the manufacturer's utility. Some machines ship set to prioritise silence over speed.
• Running a laptop closed on a desk while docked is fine on most designs, but it removes one route for heat on machines that vent through the keyboard. Give it room.

Common mistakes

• Using a laptop on a bed or a sofa for long sessions — It seals the intake vents completely. It is the single most common cause of a machine that runs hot and slow, and it costs nothing to fix.
• Blasting compressed air into the vents — It packs dust further into the fins and can over-spin the fan. It appears to work because the visible dust goes, while the mat on the fins remains.

If it doesn't work

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