Why Your Mac Got Slower After Upgrading to Tahoe — And How to Fix It

Upgrading to macOS Tahoe should give your Mac new features, security improvements and better compatibility with Apple’s wider ecosystem. However, some users notice that their Mac feels slower immediately after completing the upgrade.

Applications may take longer to open, the fans may run more frequently, battery life may fall and the Mac may become warmer than usual. Search can feel sluggish, video calls may stutter and even simple tasks may appear less responsive.

This does not necessarily mean macOS Tahoe has permanently damaged your Mac or that you immediately need a replacement. A major operating-system upgrade can trigger background work, expose compatibility problems and place additional pressure on storage, memory and older applications.

Here are the most common reasons a Mac becomes slower after upgrading to macOS Tahoe—and the practical steps you can take to improve it.

Why Can a macOS Upgrade Temporarily Slow Down Your Mac?

A major macOS upgrade replaces or changes thousands of system components. Once installation has finished, the Mac may still need to complete several tasks in the background.

These can include:

• Rebuilding the Spotlight search index.
• Resynchronising cloud files.
• Updating application databases.
• Processing email and attachments.
• Refreshing photo libraries.
• Installing application updates.
• Rechecking security permissions.
• Reconnecting backup and management services.

Apps can also continue performing background tasks when they are not visibly open, including checking for updates and synchronising data. macOS allows these activities to be reviewed through Login Items & Extensions settings. 

During this period, the Mac may use more processor, memory, storage and network capacity than it normally would.

1. Spotlight May Be Rebuilding Its Search Index

Spotlight is the search technology used throughout macOS. It helps users locate applications, files, emails, contacts and other information.

Following a major upgrade, Spotlight may need to update or rebuild parts of its index. This can create substantial background disk and processor activity, particularly on a Mac containing a large number of files.

Possible symptoms include:

• The Mac feeling generally sluggish.
• Search results appearing incomplete.
• Outlook search returning no results.
• Frequent disk activity.
• Reduced battery life.
• Fans running more often.
• Processes associated with metadata using significant resources.

Give the Mac time to complete indexing before attempting aggressive repairs. Keep it connected to power where possible and avoid repeatedly shutting it down during the process.

If Spotlight remains unreliable after the Mac has had sufficient time to settle, Apple provides a supported method for rebuilding the index by temporarily excluding a disk or folder from Spotlight and then adding it back. 

How to Rebuild the Spotlight Index

1. Open System Settings.
2. Select Spotlight.
3. Open Search Privacy.
4. Add the affected disk or folder.
5. Wait briefly.
6. Remove the same disk or folder from the exclusion list.
7. Allow Spotlight to index the location again.

Reindexing may temporarily increase background activity, so it should normally be completed when the employee does not urgently need maximum performance.

2. Your Apps May Not Be Fully Compatible With Tahoe

macOS Tahoe may expose problems in older versions of applications, extensions and device drivers.

The application may still open, but it could consume more processor time, stop responding or repeatedly attempt an unsuccessful background task.

Common examples include:

• Antivirus and endpoint-security software.
• VPN clients.
• Cloud file-sync applications.
• Printer and scanner utilities.
• Backup agents.
• Video-conferencing tools.
• Browser extensions.
• Audio and display utilities.
• Remote-support software.
• Older Microsoft 365 applications.

Before blaming the operating system, update your business applications.

Open the Mac App Store and install available updates. For applications downloaded directly from a supplier, use the application’s own update process or obtain the latest approved installer from the developer.

Business users should not remove security, management or backup software without checking with their IT provider. A security application may appear resource-intensive because it is completing a post-upgrade scan or installing a compatible system component.

3. You May Need the Latest Tahoe Update

The first version of a major operating system is rarely the final version businesses should run indefinitely. Apple releases subsequent updates to address bugs, compatibility issues, security vulnerabilities and performance problems.

Apple states that macOS Tahoe updates improve stability, performance or compatibility. At the time of writing, its update history lists macOS Tahoe 26.6, which includes bug and security fixes as well as Spotlight-index optimisation in preparation for the next macOS generation. 

To check for updates:

1. Open System Settings.
2. Select General.
3. Select Software Update.
4. Install the latest approved Tahoe update.
5. Restart the Mac.

Apple recommends backing up the Mac before installing new system software. 

On a company-managed Mac, updates may be controlled through Microsoft Intune, Apple device management or another central platform. Employees should follow the organisation’s update process rather than bypassing it.

4. Your Startup Disk May Be Too Full

A Mac needs available storage for temporary files, application caches, updates and virtual memory.

A major macOS upgrade may require additional space during and after installation. If the startup disk was already nearly full, the upgrade can leave the Mac struggling to perform normal tasks.

Apple identifies insufficient free startup-disk space as a common cause of slow performance. It recommends reviewing storage, moving unnecessary files and using macOS storage-management options. 

To check your storage:

1. Open System Settings.
2. Select General.
3. Select Storage.
4. Review the recommendations and storage categories.

Look for:

• Large downloads.
• Old macOS installers.
• Unused applications.
• Duplicate video files.
• Device backups.
• Large email attachments.
• Forgotten virtual machines.
• Files stored both locally and in the cloud.
• Old creative-project libraries.

Do not solve the problem by moving confidential business information into an unapproved personal cloud account.

If the business uses iCloud Photos, Apple offers an Optimise Mac Storage setting that keeps smaller versions locally when storage is limited while retaining full-resolution originals in iCloud. 

5. Too Many Apps May Be Opening at Login

A major upgrade can make existing startup inefficiencies more noticeable.

Applications that open automatically may compete for processor time, memory, disk access and network bandwidth as soon as the employee signs in.

To review them:

1. Open System Settings.
2. Select General.
3. Open Login Items & Extensions.
4. Review Open at Login.
5. Review applications permitted to run in the background.

Apple explains that this area controls apps, documents, folders and server connections that open automatically. It also identifies applications allowed to perform background activities such as synchronising data and checking for updates. 

Remove only items you recognise and do not need.

Do not disable:

• Endpoint protection.
• Device-management agents.
• Backup software.
• Required VPN tools.
• Approved file-sync services.
• Remote-support tools.

If removing startup items fixes the performance problem, add necessary items back one at a time. Apple recommends this process when diagnosing whether a login item is causing startup problems. 

6. One Application May Be Consuming Excessive Resources

The entire Mac can feel slow when one application or process is using excessive processor time or memory.

Use Activity Monitor to identify what is happening.

1. Open Applications.
2. Open Utilities.
3. Launch Activity Monitor.
4. Select the CPU tab.
5. Click the % CPU column to sort the list.
6. Select the Memory tab and review Memory Pressure.
7. Review the Energy and Disk tabs where appropriate.

Apple’s Activity Monitor provides information about processor, memory, disk, network and energy use. It can help identify a troublesome application or process when a Mac is sluggish or unresponsive. 

What Does Memory Pressure Mean?

The Memory Pressure graph indicates how efficiently the Mac’s memory is supporting the current workload.

• Green generally indicates that memory is being managed effectively.
• Yellow suggests that available memory is under pressure.
• Red indicates significant pressure and may correspond with noticeable slowdowns.

Activity Monitor also shows compressed memory and swap usage. Heavy swap use means the Mac is moving information between its memory and startup disk, which can make work feel less responsive—particularly if available storage is also low. 

If one application consistently consumes excessive resources:

• Save your work.
• Quit and reopen the application.
• Install its latest update.
• Disable unnecessary extensions.
• Contact its developer or your IT provider.
• Replace it if it is no longer supported.

Do not randomly force-quit unfamiliar macOS processes. Some are essential system services and will simply restart.

7. Cloud Services May Be Resynchronising

Following the upgrade, services such as iCloud Drive, OneDrive, Dropbox and Google Drive may check their local databases and resynchronise information.

This can increase:

• Network activity.
• Disk access.
• Processor use.
• Battery consumption.
• Heat output.

The effect can be particularly noticeable when the Mac contains a large SharePoint or OneDrive library.

Check the status of each approved synchronisation application. Look for warning messages, repeated failures or a queue containing an unusually large number of files.

Avoid running several overlapping file-sync tools against the same folders. This can create conflicts and duplicate activity.

For business data, confirm that files are being stored in the organisation’s approved Microsoft 365, SharePoint, OneDrive or cloud environment rather than personal accounts.

8. Outlook, Mail or Other Apps May Be Reindexing

Email applications often maintain their own local database while also relying on macOS search technologies.

After the upgrade, Outlook may need to resynchronise a mailbox or rebuild searchable information. A large mailbox containing many years of email and attachments can take time to process.

During this period, users may experience:

• Incomplete Outlook searches.
• Delayed message display.
• High processor usage.
• Increased storage activity.
• Temporary mailbox synchronisation messages.

Confirm that required messages remain available through Outlook on the web. If the web version works correctly but the Mac application does not, the issue is probably local to the Mac’s application cache, profile or index.

Avoid immediately deleting the Outlook profile. It may contain locally stored or unsynchronised information.

9. External Devices or Drivers May Be Causing the Problem

Some performance issues begin only when the Mac is connected to a particular accessory.

Possible causes include:

• Older docking stations.
• Display adapters.
• USB hubs.
• Printers.
• Audio interfaces.
• External drives.
• Network adapters.
• Security keys.
• Specialist business equipment.

Disconnect non-essential accessories and restart the Mac.

If performance improves, reconnect devices individually until the problem returns. Then check whether the accessory has current Tahoe-compatible firmware, software or drivers.

Apple uses a similar isolation process when diagnosing unexpected Mac restarts, recommending that users disconnect peripherals and reconnect them individually to identify the cause. 

Cheap or unsupported adapters can create display, charging and network problems that appear to be general macOS performance issues.

10. Safe Mode Can Help Identify Startup Software Problems

Safe mode starts the Mac with a reduced collection of software and can help determine whether an issue is caused by something loading during startup.

Apple specifically recommends safe mode for identifying problems caused by software that loads as the Mac starts. 

Starting an Apple Silicon Mac in Safe Mode

1. Shut down the Mac.
2. Press and hold the power button until Loading startup options appears.
3. Select the startup disk.
4. Hold the Shift key.
5. Click Continue in Safe Mode.
6. Sign in and test performance.

Starting an Intel Mac in Safe Mode

1. Restart the Mac.
2. Immediately press and hold Shift.
3. Release the key when the login window appears.
4. Sign in and test performance.

If the Mac works normally in safe mode, the likely cause is a startup item, extension, third-party application or other software loaded during an ordinary startup.

Restart normally to leave safe mode.

11. Your Mac May Be Compatible but Close to Its Practical Limits

Apple’s compatibility list includes a range of Macs, including Apple silicon models and a limited number of older Intel Macs. For example, Tahoe supports Apple silicon MacBook Pro models introduced from 2020, as well as certain 2019 and 2020 Intel MacBook Pro models. 

Being officially compatible means the operating system can be installed. It does not mean every supported Mac will deliver identical performance.

An older Mac may have:

• Less memory.
• Slower storage.
• Lower graphics performance.
• An ageing battery.
• Limited thermal headroom.
• Several generations of accumulated software.
• Older third-party peripherals.

If Activity Monitor repeatedly shows high memory pressure during ordinary work, the employee’s workload may now exceed the device’s practical capacity.

Memory in modern Apple silicon Macs cannot normally be upgraded after purchase, so businesses should consider realistic workloads when selecting replacement equipment.

12. Battery and Thermal Conditions Can Affect Performance

A Mac may reduce performance when it becomes excessively hot or when power-management settings prioritise battery life.

Make sure that:

• Air vents are not obstructed.
• The Mac is not being used on bedding or soft furniture.
• The correct power adapter is connected.
• The battery is charging normally.
• The device is not exposed to excessive heat.
• Demanding work is completed on mains power where practical.

Apple advises using the Mac on a hard, flat and stable surface with good ventilation when running diagnostics. 

A failing battery or charging problem can also contribute to unexpected behaviour. Check System Settings > Battery > Battery Health and arrange a professional assessment if macOS recommends service.

13. Run Apple Diagnostics if the Problem Persists

If the Mac remains unusually slow after software checks, the problem may involve hardware.

Apple Diagnostics can test components and provide reference codes for detected issues.

Before running it:

1. Install available macOS updates.
2. Shut down the Mac.
3. Disconnect non-essential devices.
4. Connect the Mac to mains power.
5. Place it on a stable, well-ventilated surface.

On Apple silicon, press and hold the power button until startup options appear, then follow the diagnostics instructions. In Tahoe, Apple Diagnostics may allow you to choose a specific diagnostic, such as one for the built-in display, keyboard or trackpad. 

Hardware diagnostics may identify issues involving components such as memory, power, sensors or storage.

14. Reinstall macOS Only as a Later Step

If the Mac remains slow and diagnostics do not identify a hardware fault, reinstalling macOS may repair damaged operating-system components.

Reinstallation should not be the first response.

Before proceeding:

• Create and verify a backup.
• Confirm access to business accounts.
• Protect locally stored files.
• Record important application licences.
• Check that FileVault recovery information is available.
• Confirm that the Mac is enrolled correctly in business management.
• Make sure the employee’s cloud files are synchronised.

Apple’s troubleshooting guidance notes that reinstalling macOS may be appropriate when diagnostics do not identify hardware problems but operating-system issues remain. 

A reinstall may preserve user information when completed correctly, but a business should still maintain a verified backup before any significant repair.

Should You Downgrade from Tahoe?

Downgrading should normally be considered only when:

• A critical business application does not support Tahoe.
• A specialist device has no compatible driver.
• A serious fault cannot be resolved through updates.
• The organisation has a tested and supported rollback process.

Downgrading can require erasing the Mac and restoring information from a compatible backup. A backup created under a newer operating system may not always restore cleanly into an older environment.

For business deployments, this is why major macOS upgrades should be piloted with a controlled group before being released across every Mac.

What Not to Do

Do Not Install Random “Mac Cleaner” Applications

Utilities promising instant speed improvements may remove caches, request extensive permissions or create more problems than they solve.

Use macOS’s built-in storage and monitoring tools or an approved business-management platform.

Do Not Delete Unfamiliar System Files

Removing files from Library or system folders without understanding their purpose can damage applications, security tools or user profiles.

Do Not Remove Company Security Software

Security, backup and management agents may use more resources temporarily after an upgrade while completing updates or scans.

Speak to your IT provider before disabling them.

Do Not Erase the Mac Without a Verified Backup

Confirm that business files, email, application data and recovery credentials are protected before carrying out a reset or reinstall.

Do Not Ignore Persistent Excessive Heat

A Mac that remains extremely hot, repeatedly shuts down or produces hardware warnings should be professionally assessed.

A Quick Tahoe Performance Checklist

Work through these steps in order:

1. Restart the Mac.
2. Allow post-upgrade background work to finish.
3. Install the latest macOS Tahoe update.
4. Update Microsoft 365 and other business applications.
5. Check available storage.
6. Review Activity Monitor.
7. Examine login and background items.
8. Check cloud-sync activity.
9. Disconnect non-essential accessories.
10. Test the Mac in safe mode.
11. Rebuild Spotlight only if search remains problematic.
12. Run Apple Diagnostics.
13. Escalate persistent problems to professional support.
14. Reinstall macOS only after backing up and completing safer checks.

Preventing Problems With Future macOS Upgrades

Businesses can reduce disruption by managing macOS upgrades rather than allowing every employee to install them immediately.

A controlled process should include:

• Checking Mac compatibility.
• Reviewing critical application support.
• Testing printers, docks and specialist devices.
• Confirming backup success.
• Piloting the upgrade with selected employees.
• Updating security and management tools first.
• Communicating expected upgrade times.
• Monitoring performance after installation.
• Maintaining a rollback plan.
• Recording any known issues.

A Mac that is centrally managed through Microsoft Intune or another device-management platform can be assessed, updated and supported more consistently.

How Hamilton Group Can Help

A slowdown after upgrading to macOS Tahoe may be temporary, but it can also reveal storage problems, outdated applications, failing hardware or unsuitable device specifications.

Hamilton Group can diagnose Mac performance issues and determine whether the cause is macOS, an application, Microsoft 365, device management, hardware or another part of your IT environment.

Our Mac support services can include:

• macOS Tahoe troubleshooting.
• Mac performance assessments.
• Application compatibility checks.
• Microsoft 365 for Mac support.
• Spotlight and Outlook search repair.
• Device and security management.
• Microsoft Intune for macOS.
• Backup and recovery.
• Hardware lifecycle planning.
• Business application testing.
• Managed macOS update deployment.
• Ongoing IT support.

Hamilton Group aims to make first contact on IT support requests within 15 minutes, helping your employees receive an early response when a Mac becomes slow or unreliable.

To discuss Mac support for your business, contact Hamilton Group on 0330 043 0069 or visit hgmssp.com.