Why is my MacBook running slow and hot?

The reason slow and hot arrive together is that they are the same event seen from two angles. A process loads the chip, the chip produces heat, and as the temperature climbs toward the chip's limit, macOS steps the clock speed down so it makes less heat. A lower clock speed is a slower chip, so the Mac feels laggy. That deliberate down-clocking is thermal throttling, and it is the chip protecting itself rather than anything breaking. It would rather feel slow for a few minutes than cook.

The loop is worth seeing clearly because it tells you where to push. The heat is the cause and the slowness is the symptom, so chasing the slowness directly gets you nowhere. You either remove the thing heating the chip, or you help the chip stay cool enough that it never reaches the temperature where macOS has to throttle. For the full mechanism, why it happens and what it is protecting, I have written a separate guide on what thermal throttling on a Mac is. For the heat side on its own, why your Mac gets so hot goes through every cause in turn.

Before you treat the heat, make sure heat is the cause, because plenty of slow Macs are not hot at all. If the Mac is cool to the touch and the fan is quiet but it still drags, this is not throttling and a fan app will do nothing for it. A nearly full disk slows everything down because macOS needs free space to work. Low memory makes the Mac swap to disk constantly, which feels slow without producing much heat. A Mac that is several years old is simply slower than it was, and no amount of cooling brings that back. And if only Safari or one heavy app is sluggish while the rest of the Mac is fine, the problem is that app, not the chip's temperature.

The tell for throttling-driven slowness is that the heat and the lag move together: the Mac is warm or hot, often with the fan up, and it speeds back up once it cools. If that matches what you see, treat the heat. If the Mac is slow while cool, fix the disk, memory, or app instead. To watch the temperature while you test, the guide on checking your Mac's temperature covers how, since macOS shows it nowhere, and how hot is too hot for a Mac sets out the bands to compare against.

If the heat and the slowness move together, the next step is to find what is heating the chip. Open Activity Monitor, click the CPU column to sort by it, and read the top of the list. A browser tab gone wrong, a sync client stuck retrying, a video call doing too much, a hung helper, or an app stuck in a loop can sit at a high percentage indefinitely with nothing obvious on screen, and while it does, the chip stays hot and macOS keeps throttling.

Quit your own apps and tabs first, not unfamiliar system processes. To force quit a frozen app, hold Option, click and hold its icon in the Dock, and choose Force Quit, or use the Force Quit window from the Apple menu. If you see something called kernel_task high in the list, leave it alone: that is macOS deliberately taking cycles to hold heat down, a symptom of the heat rather than the cause, and it can't be forced to quit. After a macOS update it is also normal for Spotlight to reindex your drive or Photos to analyze your library, which loads the chip for a stretch and then stops on its own, so if the busy process is one of those, let it finish and the throttling lifts with it.

If the process list is clean and the Mac still runs hot and slow under normal work, the next checks cost nothing. A MacBook sheds heat through its surface and, on models with a fan, through its vents. A Mac on a bed, a sofa cushion, or a soft case has its vents partly blocked and its body insulated, so the same load keeps it hotter and it throttles sooner. Get it onto a hard, flat surface and the baseline drops, which often lets it stop throttling.

Ambient temperature is the other free lever. A warm room or a patch of direct sun raises the floor the chip starts from, so it reaches the throttling point faster. Move somewhere cooler and there is more headroom before macOS has to step in. On older machines, dust matters too: years of it in the vents and on the blades keeps heat in long after a newer Mac would have cleared it, and a clean-out helps. None of this is glamorous, but it is real and it is free. For the full set of cooling steps in order, how to fix an overheating Mac walks through them.

Sometimes the process list is clean, the vents are clear, the room is cool, and the Mac still throttles under ordinary work. This is where the macOS fan curve being cautious shows up. macOS tends to let the chip warm up a fair way before it ramps the fans hard, so on a sustained load the chip can reach the throttling point while the fans are still spinning up. The fans get there eventually, but by then the Mac has already felt slow. A related symptom is a fan that keeps running and never spins down, which is the same caution from the other side.

The honest catch is that macOS gives you no way to make the fans react earlier yourself. There is no slider in System Settings and no supported Terminal command, so on stock macOS you are at the mercy of the curve. That is the gap a fan control app fills: instead of waiting for macOS to ramp, you spin the fans up sooner so the chip stays under the throttling point and keeps its speed.

Here is the limit stated plainly first: no app can cool a chip below what the fans can physically move, so software can't rescue a Mac that is slow for a reason other than heat. If the disk is full, the memory is low, or the machine is simply old, fix that, which is why the checks above come first. What software can change is when the fans react.

ChillBlades lets you take a fan off the macOS curve. With Auto Boost, every Auto fan spins up when the hottest sensor reaches a band you pick, then eases off once it falls back below it, so the fans get ahead of the heat instead of trailing it. By moving more air earlier, the chip stays under the temperature where macOS would throttle, so it holds its clock speed and the Mac stays responsive under the same load. You can also switch a fan to a fixed speed with a slider that runs only across that fan's real hardware range, clamped at both ends so you can't push it past its rated maximum or stop it dead, and the chip protects itself regardless. The trade is honest: earlier, faster fans are louder, so it suits sustained work where you would rather keep the speed than keep it silent. The moment you quit ChillBlades every fan goes straight back to macOS automatic control, so the default is always one quit away.

For the related heat symptoms, there is a guide on what happens when your MacBook overheats and the screen goes black or it shuts down, and the quick questions are answered in the FAQs.

I make ChillBlades, a Mac fan control app, and I write these guides, so I spend a lot of time on why these machines run hot and slow. I have kept this honest rather than promotional: most slow-and-hot MacBooks come down to a runaway process or trapped heat, and plenty of slow Macs are not hot at all, where a full disk, low memory, or age is the real problem and no fan app helps. Where an app genuinely helps is throttling-driven slowness, by spinning the fans up earlier so the chip stays cool enough to keep its speed. Apple does not publish its fan curves, so treat this as practical guidance from working with the hardware, not a spec sheet. Your Mac protects itself regardless of what any app does. The ChillBlades behavior described here runs on M1 through M5 and Intel Macs with fans, on macOS 13 and later; the base fanless MacBook Air has no fan to control, so it can only throttle to cool down.