Before concluding your Mac is broken, work through these steps. Most Mac slowdowns are caused by software issues that don't require any hardware intervention.
1. Check Activity Monitor First
Open Activity Monitor (search it in Spotlight). Sort by CPU%. If any process is using 80–100% CPU constantly, that's your problem. "kernel_task" using high CPU is often macOS throttling the CPU due to heat — the Mac is protecting itself from overheating.
2. Restart (Properly)
MacOS handles sleep and wake well but the system benefits from a full reboot. Use Apple Menu → Restart. Not sleep, not just closing the lid — an actual restart clears memory pressure and resets processes that may have grown bloated.
3. Check Storage Space
macOS needs free space to operate. With less than 15–20% free, performance degrades significantly. Apple Menu → About This Mac → Storage. If you're below 20GB free, clearing space should be priority one.
4. Update macOS
Apple regularly releases performance improvements through macOS updates. If you've been deferring updates, check System Settings → General → Software Update. The latest macOS often runs noticeably better than two versions back.
5. Manage Login Items
Apps set themselves to launch at startup without asking. Go to System Settings → General → Login Items. Remove anything you don't need immediately on boot — Dropbox, Adobe Creative Cloud, Steam, and similar apps are common culprits.
6. Reindex Spotlight
A corrupted Spotlight index can cause high CPU usage from the "mds" process. Go to System Settings → Siri & Spotlight → Spotlight Privacy, add your startup drive to the exclusion list, then remove it again. This triggers a reindex.
7. Check for Malware
Macs do get malware, less commonly than Windows but it does happen. Run a free Malwarebytes scan for Mac. Adware and browser extensions are more common culprits on Mac than traditional viruses.
When It's Actually Hardware
If the Mac is slow even on a freshly installed macOS with nothing else running, it may be time for an SSD upgrade (if it has a mechanical hard drive) or a RAM upgrade. M-series Macs don't allow RAM upgrades after purchase, so check this before buying.