Why Your Mac Feels Slow (and the Proven Fixes That Actually Work)

Most "fix your slow Mac" articles exist to sell you cleanup software. This one does not. A slow Mac running macOS Tahoe 26 has a diagnosable cause, and once you identify it, the fix is specific and fast. The four most common culprits are Spotlight reindexing consuming CPU after an update, Liquid Glass transparency effects overworking the GPU, low free storage triggering aggressive memory swapping, and an Electron app rendering bug that Apple patched in macOS 26.2. Open Activity Monitor (press Command-Space, type "Activity Monitor," hit Return), check what is actually eating your resources, and match it to the right fix below.

Key Takeaways

• Open Activity Monitor and sort by CPU to identify the exact process dragging your Mac down.
• Spotlight reindexing after a Tahoe update takes 24 to 48 hours. Let it finish before assuming something is broken.
• Reduce Transparency in System Settings to immediately stop Liquid Glass from straining your GPU.
• Keep at least 15 percent of your internal storage free. Below 10 percent, macOS swaps to disk and everything crawls.
• Update to macOS Tahoe 26.2 or later. Apple blocked the Electron app bug that caused system-wide stuttering.
• Run a single Terminal command to kill persistent input lag caused by Tahoe's autofill heuristic.

This table maps each symptom to its cause and fix so you can jump directly to the section that applies to your Mac:

Slow Mac Diagnosis: At-A-Glance

How to Read Activity Monitor Like a Diagnostic Tool

Every fix in this article starts here. Activity Monitor is the reason you do not need a third-party scanner, because it shows you exactly which process is consuming your Mac's resources, by name, in real time.

Open Activity Monitor from Applications, then Utilities. Click the CPU tab and sort by "% CPU" descending. Write down the top two or three processes. Are they system processes like mds and mdworker, or third-party apps? Then click the Memory tab and look at the "Memory Pressure" graph at the bottom of the window. Green means healthy. Yellow means your Mac is compressing memory to keep up. Red means it is swapping to disk, and that is the single biggest performance killer on any Mac because disk I/O is orders of magnitude slower than RAM access, even on Apple Silicon machines with fast internal SSDs.

Those two data points, your top CPU consumers and your memory pressure color, tell you which section below to read. Skip everything that does not apply. If you want to automate repetitive diagnostic checks, you can build powerful AI Shortcuts on Mac with Apple Intelligence to create one-tap workflows that surface this information faster.

"mds" and "mdworker" Are Eating Your CPU: That Is Spotlight Reindexing

macOS Tahoe 26 introduced deeper system indexing for Spotlight, Apple Intelligence features, and the Photos library. After any Tahoe update, including incremental ones like 26.1 to 26.2, your Mac quietly reindexes every file on disk. On a Mac with a terabyte of data, this process can pin the CPU for 24 to 48 hours straight.

The friction is subtle but maddening. Your Mac feels laggy, but nothing obvious seems wrong. Fan noise creeps up on a MacBook Pro. Even an Apple Silicon M4 with 32 GB of unified memory feels sticky while indexing runs in the background. Here is the critical detail: closing the lid on a MacBook pauses indexing and stretches the process out over days instead of hours. Leave your Mac plugged into power and awake overnight. Let it grind through the work.

If indexing still seems stuck after 48 hours, reset it. Open Terminal and type:

sudo mdutil -E /

Press Return and enter your password. This erases and rebuilds the entire Spotlight index from scratch. Expect another 12 to 24 hours of reindexing, but a fresh start often resolves corrupted index files the update created. Multiple Apple Community users reported that deleting all files inside ~/Library/Metadata/CoreSpotlight/ and restarting resolved severe lag that persisted for days, even on M4 Pro MacBook Pro models with 48 GB of RAM and 1.4 TB of free storage. That tells you the problem is the index, not the hardware.

Liquid Glass Is Beautiful and It Is Hammering Your GPU

Tahoe's Liquid Glass design language refracts and reflects content behind every window sidebar, toolbar, and menu bar in real time. On Apple Silicon M1 and M2 Macs, this rendering overhead causes visible frame drops when resizing windows, pulling down menus, or swiping between desktops.

The fix takes five seconds. Open System Settings, click Accessibility in the sidebar, then click Display. Toggle on "Reduce Transparency." Window chrome turns opaque, menu bars lose their blur, and GPU usage drops immediately. One widely documented observation: users on Apple Silicon M2 Macs with 24 GB of RAM saw choppy animations return instantly every time they toggled transparency back on, even months after installing Tahoe. That points to a GPU-bound rendering cost, not a temporary post-update issue. Reduce Transparency is the single fastest lever specific to macOS Tahoe, and Apple documents it on their support page for slow Macs at https://support.apple.com/guide/mac-help/if-your-mac-runs-slowly-mchlp1731/mac as one of the recommended performance steps.

Update to macOS 26.2 (This One Actually Matters)

Not all macOS updates are equal. The 26.2 update, released in late 2025, fixed a specific, serious performance regression. Certain Electron-based apps, including Slack, Discord, and Visual Studio Code, were overriding macOS window corner masks using private APIs. This caused the system rendering pipeline to struggle, producing stuttering and lag across the entire Mac, not just in the offending app. The lag appeared even when scrolling in Safari or dragging Finder windows, as long as one of these Electron apps was visible on screen.

macOS 26.2 blocks this behavior at the system level. You get smoother scrolling and normal window performance even with older Electron apps still installed. The update also improved memory handling: the system releases unused RAM faster and reduces CPU load during sustained workloads. As of February 2026, macOS 26.2.1 is the latest stable release, with 26.3 in beta.

Check your version: System Settings, then General, then Software Update. If you are still on 26.0 or 26.1, this single update may resolve most of what you have been experiencing.

Fix the Typing Lag Nobody Talks About

A lesser-known Tahoe issue causes a slight but persistent delay between pressing a key and seeing the character appear. It shows up across text fields in Safari, Notes, Mail, and third-party apps. The culprit is a native autofill heuristic that scans on every keystroke. Community developers traced it to a macOS-level process running underneath every text input.

Open Terminal and run:

defaults write -g NSAutoFillHeuristicControllerEnabled -bool false

Restart any open apps for the change to take effect. Keystroke response snaps back to what you expect from a Mac. This is not a hack or a workaround. It disables a background scanning feature that was never intended to introduce perceptible latency, and Apple has not yet addressed it in a point release.

Your Storage Is Fuller Than You Think

macOS Tahoe needs breathing room. When internal storage dips below 10 percent free, the system leans heavily on swap files, and virtual memory operations slow everything to a crawl. This hits harder than you might expect: even an Apple Silicon M4 Max MacBook Pro feels sluggish when swap activity spikes, because the CPU stalls waiting for disk I/O that is thousands of times slower than a RAM read.

Check your available space: System Settings, then General, then Storage. The bar graph shows a breakdown by category. If your Mac is above 85 percent full, performance is suffering whether you notice it or not.

Start with the built-in recommendations macOS offers on that same Storage screen: optimize iCloud storage, empty the Trash automatically, review large files. Move completed projects, media libraries, or Xcode device images off the internal drive.

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Clean Up Login Items and Background Daemons

Third-party apps that launch at startup accumulate over months. Open System Settings, click General, then Login Items & Extensions. Two sections matter: "Open at Login" lists apps that launch visibly, and "Allow in the Background" lists daemons and agents that run silently. Disable anything you do not need running at all times. Anti-virus tools, system "optimizers," and old printer utilities are the usual offenders.

A specific edge case worth knowing: some users found that BackgroundShortcutRunner, a process tied to Apple Shortcuts, consumed abnormally high CPU in macOS Tahoe. Disabling complex Shortcuts automations temporarily, then re-enabling them one by one, isolated which automation triggered the spike. This kind of targeted diagnosis is exactly what Activity Monitor enables and what no cleanup app can replicate for you.

Accessibility and Clarity

The Reduce Transparency toggle discussed above doubles as an accessibility feature. It benefits users with low vision or light sensitivity by replacing translucent surfaces with solid backgrounds, improving text contrast and reducing visual noise. VoiceOver works with every System Settings panel referenced in this guide, including Activity Monitor, Storage settings, and Login Items.

For cognitive accessibility, each fix in this article has its own heading and can be read independently. There is no dependency between sections. Pick the fix that matches what Activity Monitor tells you and skip everything else. The checklist below is structured for screen readers and can be copied directly into a note or task manager.

Quick-Action Checklist

1. Open Activity Monitor (Command-Space, type Activity Monitor, press Return).
2. CPU tab: sort by % CPU. Note the top processes by name.
3. Memory tab: check Memory Pressure graph. Green is fine. Yellow means compression. Red means swapping.
4. If mds or mdworker dominates CPU: leave Mac plugged in and awake overnight. Still slow after 48 hours? Run sudo mdutil -E / in Terminal.
5. If window animations stutter: System Settings, then Accessibility, then Display, then toggle Reduce Transparency on.
6. If running macOS 26.0 or 26.1: System Settings, then General, then Software Update. Install 26.2 or later.
7. If typing feels delayed: run defaults write -g NSAutoFillHeuristicControllerEnabled -bool false in Terminal, then restart apps.
8. If storage exceeds 85% full: System Settings, then General, then Storage. Follow recommendations. Offload large files to external SSD.
9. System Settings, then General, then Login Items & Extensions. Disable non-essential startup apps and background agents.