Why is my MacBook running slow? 9 fixes before you book a repair

A slow MacBook is one of the most common complaints we hear from customers in Chester and across North Wales — and the good news is, most of the time you can fix it yourself in about half an hour. Before you book a repair (or, worse, give up and buy a new Mac), work through this list. These are the same nine checks an Apple repair engineer would run before opening up the case.

This guide covers both Intel-based MacBooks (2006–2020) and Apple Silicon MacBooks (M1, M2, M3, M4 — 2020 onwards). The order matters — start at step 1 and work down. If you’ve tried something already, skip it. By the end, your MacBook will either be running noticeably faster, or you’ll know what kind of repair it genuinely needs.

A note on safety: every step in this guide is safe to do yourself. Nothing here will void your warranty, damage your data, or risk your device.

1. Check what’s actually using your CPU and RAM

Open Activity Monitor (search for it in Spotlight, or find it under Applications → Utilities). Click the CPU tab and sort by % CPU (descending). Then click the Memory tab and sort by Memory (descending).

What you’re looking for: any process eating more than 30–40% of CPU continuously, or any single app using more than 4–5 GB of RAM.

Common culprits we see:

• Google Chrome — particularly with many tabs open. Chrome can eat 8GB+ of RAM by itself
• Microsoft Teams or Zoom — known memory hogs even when minimised
• Spotify — uses surprising amounts of CPU
• kernel_task — if this is over 50% CPU, your Mac is probably overheating (see step 8)
• mds or mdworker — Spotlight indexing; should calm down within an hour

If you see a runaway process, click it and hit the X in the top-left to quit it. If it keeps coming back, that app has a problem — uninstall it or look for an update.

2. Restart properly (not “close the lid and hope”)

Most MacBook users close the lid for sleep and rarely fully restart. macOS handles this well — until it doesn’t. After a couple of weeks of sleep-and-wake cycles, memory gets fragmented, background processes pile up, and everything slows down.

The fix: Apple menu → Restart. Choose “Reopen windows when logging back in” if you want to keep your apps. The whole thing takes 60 seconds. Most “my MacBook is slow” calls we get are solved by this single step.

Do this once a week as a habit.

3. Check your free storage space

A nearly-full SSD makes a MacBook crawl. macOS uses free SSD space as overflow memory (“swap”), so when you fall below about 15% free, performance falls off a cliff.

To check: Apple menu → About This Mac → More Info → Storage. (On older macOS: → Storage tab directly.)

If you’re under 15% free, you need to clear space. The fastest wins:

• Empty the Trash (right-click the Trash icon → Empty)
• Delete the Downloads folder contents (or sort by size and delete the biggest)
• Clear the Mail Downloads folder at ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads
• Delete old iOS backups — Finder → Manage Backups (these can be 30GB+ each)
• Offload Photos to iCloud or an external drive if your library is huge

Aim for at least 20% free space.

4. Disable login items you don’t need

Every app that launches at login uses CPU, memory, and slows your boot. Most have no reason to be there.

System Settings → General → Login Items & Extensions (on macOS Ventura and later). Look at the “Open at Login” list. Anything you don’t actively need should be removed — click the app, then the minus button.

Common offenders to remove: Spotify, Microsoft Teams, Dropbox (only if you don’t use it daily), Adobe Creative Cloud, OneDrive, Google Drive.

5. Clear the cache (the right way)

Most “Mac cleaner” apps you’ll see advertised are scams or worse — they’ll show you fake problems and try to charge £40 to “fix” them. Don’t use them.

Genuine cache clearing on macOS is simple:

1. Open Finder
2. Press Shift + Cmd + G and type ~/Library/Caches
3. Select all (Cmd + A)
4. Move to Trash (Cmd + Delete)
5. Empty Trash and restart

This is safe — macOS will rebuild any caches it actually needs.

6. Reset SMC and NVRAM (Intel Macs only)

If you have an Intel-based MacBook (2006–2020), an SMC and NVRAM reset can clear persistent slow-down issues caused by power-management glitches.

To reset SMC (Intel MacBooks with T2 chip — 2018 onwards):

1. Shut down
2. Hold Control + Option (left) + Shift (right) for 7 seconds
3. While still holding those, also hold the power button for 7 more seconds
4. Release everything, then press power to turn on

To reset NVRAM (any Intel Mac):

1. Shut down
2. Turn on and immediately hold Option + Cmd + P + R
3. Hold for about 20 seconds, then release

Apple Silicon Macs (M1/M2/M3/M4) don’t have SMC or NVRAM in the traditional sense — these resets aren’t applicable and macOS handles equivalent functions automatically. If you have an M-series Mac, skip this step.

7. Update macOS

Old macOS versions can run slow on newer hardware (and vice versa). Apple regularly ships performance fixes in point releases.

System Settings → General → Software Update. Apply any pending updates. This can take 30–60 minutes and will require a restart, so do it when you don’t need the Mac.

A note: if you’re on a much older Mac (2015 or earlier), updating to the very latest macOS can actually make things slower. For very old hardware, sometimes staying on an older macOS version is faster.

8. Check for overheating

If kernel_task is using high CPU (you’d have seen this in step 1), your Mac is probably overheating. macOS deliberately throttles performance to prevent thermal damage.

Check:

• Is the Mac on a hard surface? A bed, sofa, or carpet blocks the vents
• Is the fan spinning? (You can hear or feel it on Intel Macs; M-series Macs are usually silent until under heavy load)
• Is the bottom of the case hot? Particularly hot near the hinge?

If the Mac is overheating with no obvious load, the most likely cause is dust in the fans or dried-out thermal paste between the CPU and the heatsink. This is the most common reason older MacBook Pros slow down — and unfortunately, it’s not a DIY fix (Apple has used proprietary glue and screws since 2015). Get a quote for a thermal service →.

9. Run Apple Diagnostics

If you’ve worked through everything above and the Mac is still slow, run Apple’s built-in hardware diagnostics. This will tell you if there’s a hardware fault that no software fix can address.

On Intel Macs:

1. Shut down
2. Turn on and immediately hold D
3. Let go when the diagnostic screen appears

On Apple Silicon Macs:

1. Shut down
2. Press and hold the power button until “Loading startup options” appears
3. Press Cmd + D

Apple Diagnostics will run for 2–3 minutes and either give your Mac a clean bill of health (in which case the issue is software, not hardware), or report an error code. If you get an error code, write it down — we can help you interpret it.

When it’s a real repair issue

If you’ve worked through all nine steps and your MacBook is still slow, you’re probably looking at one of these genuine hardware issues:

• Dried thermal paste / dust-clogged fans — the most common slow-MacBook cause we see at Compufix. Service usually £80–£120, returns the Mac to near-new performance.
• Failing SSD — particularly common on older MacBook Airs. Symptoms: slow boots, beach-ball spinner, kernel panics. SSD replacement starts from £100.
• Failing RAM — rare but possible on older Macs. Diagnosed in workshop.
• Logic board issue — usually shows as random freezes, kernel panics, or display issues alongside slowness.

We diagnose all of the above in our Chester workshop with a free, no-obligation quote before any work begins.

How Compufix can help

If you’re in Chester, Mold, Wrexham, or anywhere across North Wales and want a professional opinion before paying for a repair, we offer:

• Free no-obligation diagnostic — bring it in, or we’ll collect
• Honest assessment — if your Mac isn’t worth repairing, we’ll tell you
• 90-day warranty on all repairs
• No fix, no fee — if we can’t speed it up, you don’t pay

📞 Call us on 01244 728191 or get an instant quote online →