macOS Tahoe Calendar & Reminders Complete Troubleshooting Guide 2025: Fix Sync Issues, iCloud Errors, and Missing Events

macOS Tahoe 26 brings a stunning Liquid Glass redesign to Calendar and Reminders apps, but many users have encountered frustrating sync issues, error messages, and missing events after updating. This comprehensive guide provides step-by-step solutions for every Calendar and Reminders problem, from the notorious kEKAccountErrorDomain Error 9 to persistent iCloud sync failures.

Executive Summary: Calendar & Reminders Issues in macOS Tahoe 26

Key Issues Addressed in This Guide

macOS Tahoe 26 introduced significant changes to Calendar and Reminders apps, including the new Liquid Glass design and deeper Apple Intelligence integration. However, these changes have created compatibility challenges that affect millions of users.

Most Common Problems Covered:

• kEKAccountErrorDomain Error 9: The most reported Calendar error after Tahoe update
• Events Not Syncing: Calendar events failing to sync across iCloud devices
• Reminders Disappearing: Tasks and reminders vanishing after macOS update
• High CPU Usage: CalendarAgent consuming excessive system resources
• iCloud Terms Blocking Sync: New Terms and Conditions preventing calendar access
• Quick Entry Bug: Character skipping when typing quickly in Reminders

What You'll Learn:

• Step-by-step troubleshooting procedures for every major issue
• Terminal commands for advanced cache reset and database repair
• When to use third-party alternatives like Fantastical, BusyCal, or Things 3
• Prevention strategies to avoid future sync problems
• New features in Tahoe Calendar and Reminders worth using

Issue Frequency Analysis

Based on community reports and support forums from September to November 2025:

Issue	Frequency	Severity	Time to Fix
kEKAccountErrorDomain Error 9	Very High	Critical	5-10 minutes
Calendar sync stopping	High	High	10-30 minutes
Events not appearing	Moderate-High	Medium	5-15 minutes
CalendarAgent high CPU	Moderate	Medium	10-20 minutes
Reminders not syncing	Moderate	Medium	15-30 minutes
Quick entry character loss	Low-Moderate	Low	No fix (bug)

Part 1: Calendar App Troubleshooting

Understanding the kEKAccountErrorDomain Error 9

The most frequently reported Calendar issue after updating to macOS Tahoe 26 is the kEKAccountErrorDomain Error 9. This error prevents Calendar from syncing and typically appears with messages like "The server responded with an error" or "Cannot connect to the server."

Root Cause Analysis:

The primary cause of this error is that Apple updated its iCloud Terms and Conditions with macOS Tahoe 26. Users who haven't accepted the new terms will experience sync failures across all iCloud-connected apps, including Calendar, Reminders, Notes, and iCloud Drive.

Primary Solution - Accept New Terms and Conditions:

1. Open System Settings (Apple menu > System Settings)
2. Click on your Apple ID at the top of the sidebar
3. Select iCloud from the options
4. Look for a notification about Terms and Conditions
5. Click Accept to agree to the updated terms
6. Wait 30-60 seconds for settings to apply
7. Open Calendar and press Cmd+R to refresh

If No Terms Prompt Appears:

Some users report not seeing the Terms and Conditions prompt. In this case:

1. Go to System Settings > [Your Name] > iCloud
2. Toggle Calendars OFF
3. Wait 10 seconds
4. Toggle Calendars back ON
5. The Terms prompt should now appear
6. Accept the terms and restart Calendar

Calendar Events Not Syncing Across Devices

When calendar events created on your Mac don't appear on iPhone or iPad (or vice versa), the issue typically involves account configuration or cache corruption.

Quick Fix - Toggle Calendar Sync:

1. Open System Settings > [Your Name] > iCloud
2. Scroll down to find "Calendars"
3. Turn the toggle OFF
4. Wait 10 seconds (important!)
5. Turn the toggle back ON
6. Open Calendar app
7. Press Cmd+R to force refresh
8. Wait for sync to complete (status shows "Updating...")

Check Default Calendar Setting:

A common cause of sync issues is having the wrong default calendar selected:

1. Open Calendar app
2. Go to Calendar > Settings (or Cmd+,)
3. Click the General tab
4. Check the Default Calendar dropdown
5. Ensure it's set to an iCloud calendar, not "On My Mac"
6. Click Default Alert and verify alert settings

Verify Internet Accounts Configuration:

1. Open System Settings > Internet Accounts
2. Click on your iCloud account
3. Verify Calendars checkbox is enabled
4. If using Google Calendar, verify Google account is configured
5. Toggle off and on if sync isn't working

Calendar Cache Reset Procedure

When basic troubleshooting fails, a complete cache reset often resolves persistent Calendar issues.

Step 1: Export Calendar Backup

Before clearing any data, always create a backup:

1. Open Calendar app
2. Go to File > Export > Calendar Archive
3. Save the archive to your Desktop or Documents folder
4. This creates a complete backup of all calendars and events

Step 2: Force Quit Calendar Processes

Using Activity Monitor:

1. Open Activity Monitor (Applications > Utilities)
2. Click the Search field (top right)
3. Type "calendar"
4. Select each process and click the X button to force quit:
   • Calendar
   • CalendarAgent
   • CalNCService
   • CalendarNotification

Or use Terminal:

# Kill all Calendar-related processes
killall Calendar
killall CalendarAgent
killall CalendarAgent.CalNCService

Step 3: Clear Cache Files

Navigate to and delete these cache files:

# Open Finder and go to:
# ~/Library/Calendars/

# Delete these files:
# - Calendar Cache
# - Calendar Cache-shm
# - Calendar Cache-wal

# Terminal command to delete cache:
rm -f ~/Library/Calendars/Calendar\ Cache*

Step 4: Clear Container Data (If Needed)

For persistent issues, also clear container data:

# Remove CalendarAgent container data
rm -rf ~/Library/Containers/com.apple.CalendarAgent/Data/Library/Calendars/*

# Remove iCal container data
rm -rf ~/Library/Containers/com.apple.iCal/Data/Library/Calendars/*

Step 5: Restart and Rebuild

1. Restart your Mac completely (not just restart - full shutdown)
2. After restart, open Calendar
3. Press Cmd+R to force refresh
4. Wait for calendars to fully sync (may take 5-10 minutes)
5. Verify all events appear correctly

CalendarAgent High CPU Usage Fix

Some users report CalendarAgent consuming 80% or more CPU, causing system slowdowns and battery drain.

Diagnosis:

1. Open Activity Monitor
2. Click CPU tab
3. Sort by % CPU (click column header)
4. Look for CalendarAgent usage

Normal usage: Less than 5% CPU Problem usage: More than 20% sustained CPU

Solution 1 - Disable Siri Calendar Suggestions:

1. Go to System Settings > Siri & Spotlight
2. Click Siri Suggestions & Privacy
3. Find Calendar in the list
4. Toggle OFF Siri suggestions for Calendar
5. Restart your Mac

Solution 2 - Delete Old Completed Reminders:

Surprisingly, old completed Reminders can cause Calendar performance issues:

1. Open Reminders app
2. Click Completed in the sidebar
3. Delete old completed reminders (especially those older than 6 months)
4. This reduces the database size and improves performance

Solution 3 - Remove Problematic Accounts:

If CalendarAgent CPU usage spiked after adding a new account:

1. Go to System Settings > Internet Accounts
2. Identify recently added accounts (Google, Exchange, etc.)
3. Try removing the account temporarily
4. Monitor CPU usage
5. Re-add the account if needed

Calendar Opens to Wrong Day or Week

A known bug in macOS Tahoe 26.0 and 26.1 caused Calendar to open to the wrong day or week view.

Status: This issue was mostly fixed in macOS 26.1 Beta 3 and fully resolved in macOS 26.2 Beta 2.

Solution:

1. Update to the latest macOS Tahoe version
2. Go to Apple menu > System Settings > General > Software Update
3. Install any available updates
4. Restart your Mac after updating

Temporary Workaround (if update not available):

1. Open Calendar
2. Press Cmd+T to go to Today
3. This resets the view to the current date

Part 2: Reminders App Troubleshooting

Reminders Not Syncing After Tahoe Update

The Reminders app shares much of its sync infrastructure with Calendar, so many solutions overlap.

Quick Fix - Force Refresh via Calendar:

Interestingly, refreshing Calendar also refreshes Reminders:

1. Open Calendar app
2. Go to View > Refresh Calendar (or Cmd+R)
3. Wait for refresh to complete
4. Open Reminders - lists should now sync

Toggle iCloud Reminders:

1. Go to System Settings > [Your Name] > iCloud
2. Toggle Reminders OFF
3. Choose "Keep on This Mac" when prompted
4. Wait 10 seconds
5. Toggle Reminders back ON
6. Choose "Merge" when prompted
7. Wait for sync to complete

Check iCloud Storage:

If iCloud storage is full, Reminders won't sync:

1. Go to System Settings > [Your Name] > iCloud
2. Check iCloud Storage bar at the top
3. If nearly full, free up space or upgrade storage
4. Reminders requires available iCloud storage to sync

Reminders Disappearing After Update

If reminders disappeared after updating to macOS Tahoe:

Step 1 - Check All Lists:

1. Open Reminders
2. Look at the sidebar for all lists
3. Some lists may have been moved to "Other" or hidden
4. Click View > Show Sidebar if not visible

Step 2 - Check "Completed" Section:

1. Click Completed in the sidebar
2. Look for missing reminders marked as completed
3. Right-click to mark as incomplete if needed

Step 3 - Verify iCloud Account:

1. Go to System Settings > Internet Accounts
2. Click your iCloud account
3. Verify Reminders is checked
4. If unchecked, enable it and wait for sync

Step 4 - Check Other Devices:

1. Open Reminders on iPhone or iPad
2. Verify reminders appear there
3. If reminders exist on other devices but not Mac, the issue is Mac-specific
4. Try signing out and back into iCloud on Mac

Quick Entry Character Skipping Bug

A known bug in macOS Tahoe causes characters to be skipped when typing quickly in Reminders, especially in the Scheduled view.

Status: This is a confirmed bug as of macOS 26.1. The animation in Scheduled view causes input lag.

Workarounds:

1. Type slower: The bug is triggered by fast typing
2. Use a different view: Switch to Today or another view
3. Use Spotlight: Create reminders via Spotlight instead:
   • Press Cmd+Space
   • Type "Remind me to [task] at [time]"
   • Press Enter to create reminder

Alternative Solution - Use Siri:

1. Activate Siri (hold Cmd+Space or say "Hey Siri")
2. Say "Remind me to [task] at [time]"
3. This bypasses the typing bug entirely

Force Quit remindd Process

For persistent Reminders issues, force quitting the background process can help:

Using Activity Monitor:

1. Open Activity Monitor
2. Search for "remindd"
3. Select the process
4. Click the X button to force quit
5. Open Reminders - the process will restart automatically

Using Terminal:

# Force quit remindd
killall remindd

# Verify it restarted
ps aux | grep remindd

Part 3: iCloud Configuration and Sync

Complete iCloud Account Reset

When nothing else works, a complete iCloud sign-out and sign-in often resolves persistent sync issues.

Important: This will temporarily remove all iCloud data from your Mac. Ensure you have backups.

Step 1 - Backup Important Data:

1. Export Calendar archive (File > Export > Calendar Archive)
2. Note any local-only reminders
3. Ensure iCloud backup is current on other devices

Step 2 - Sign Out of iCloud:

1. Go to System Settings > [Your Name]
2. Scroll to the bottom
3. Click Sign Out
4. When prompted about keeping copies:
   • Keep copies of Calendars
   • Keep copies of Reminders
   • Keep copies of Contacts
5. Wait for sign-out to complete

Step 3 - Restart Mac:

1. Completely shut down your Mac
2. Wait 30 seconds
3. Power on

Step 4 - Sign Back Into iCloud:

1. Go to System Settings > Sign In
2. Enter your Apple ID and password
3. Complete two-factor authentication
4. Wait for iCloud to sync (may take 10-15 minutes)
5. Enable Calendar and Reminders sync when prompted

Verify Date, Time, and Timezone Settings

Incorrect date/time settings can cause sync failures:

1. Go to System Settings > General > Date & Time
2. Enable Set time and date automatically
3. Click Time Zone tab
4. Enable Set time zone automatically using your current location
5. Verify the displayed date and time are correct

Network and VPN Troubleshooting

VPNs frequently interfere with iCloud sync:

Test Without VPN:

1. Disconnect from any VPN
2. Try syncing Calendar and Reminders
3. If sync works, the VPN is the issue

VPN Workarounds:

1. Configure VPN to exclude Apple services
2. Use split tunneling if available
3. Contact VPN provider for iCloud compatibility
4. Consider alternatives that work with iCloud

For comprehensive VPN troubleshooting, see our VPN Troubleshooting Complete Guide.

Part 4: Terminal Commands and File Locations

Critical File Locations Reference

Understanding where Calendar and Reminders store their data helps with advanced troubleshooting:

Calendar Data Locations:

~/Library/Calendars/                              # Main calendar data
~/Library/Calendars/Calendar Cache               # Primary cache file
~/Library/Calendars/Calendar Cache-shm           # Shared memory file
~/Library/Calendars/Calendar Cache-wal           # Write-ahead log

~/Library/Containers/com.apple.CalendarAgent/    # CalendarAgent container
~/Library/Containers/com.apple.iCal/             # Calendar app container
~/Library/Preferences/com.apple.iCal.plist       # Calendar preferences

Reminders Data Locations:

~/Library/Reminders/                             # Main reminders data
~/Library/Containers/com.apple.reminders/        # Reminders app container
~/Library/Preferences/com.apple.reminders.plist  # Reminders preferences

Useful Terminal Commands

Check Calendar Database Integrity:

# Verify Calendar database
sqlite3 ~/Library/Calendars/"Calendar Cache" "pragma integrity_check;"

# Expected output: "ok"
# If corrupted, delete cache and let it rebuild

View Calendar-Related System Logs:

# Stream real-time Calendar logs
log stream --predicate 'eventMessage contains[cd] "calendar"' --level debug

# View recent Calendar errors
log show --predicate 'eventMessage contains "calendar" AND eventMessage contains "error"' --last 1h

Check Running Calendar Processes:

# List all calendar-related processes
ps aux | grep -i calendar

# Check CalendarAgent status
launchctl list | grep calendar

Reset Calendar Preferences:

# Remove Calendar preferences (app will recreate defaults)
rm ~/Library/Preferences/com.apple.iCal.plist

# Remove Reminders preferences
rm ~/Library/Preferences/com.apple.reminders.plist

Database Rebuild Procedure

For severe corruption, a complete database rebuild may be necessary:

# 1. Quit all Calendar processes
killall Calendar CalendarAgent 2>/dev/null

# 2. Backup existing calendar data
cp -R ~/Library/Calendars ~/Library/Calendars.backup

# 3. Remove all cache files
rm -f ~/Library/Calendars/Calendar\ Cache*

# 4. Remove container caches
rm -rf ~/Library/Containers/com.apple.CalendarAgent/Data/Library/Calendars/*
rm -rf ~/Library/Containers/com.apple.iCal/Data/Library/Calendars/*

# 5. Restart your Mac, then open Calendar
# The database will rebuild from iCloud

Part 5: Third-Party Calendar Account Integration

Google Calendar Integration Issues

Google Calendar is one of the most commonly used third-party calendar services, and macOS Tahoe 26 introduced some compatibility challenges.

Common Google Calendar Problems:

Issue	Symptom	Solution
Events not syncing	New events don't appear	Re-authenticate Google account
Duplicate events	Same event appears multiple times	Remove and re-add account
Missing calendars	Some calendars don't show	Check calendar visibility in Google
Authentication failures	Password errors despite correct credentials	Use App Password instead

Step-by-Step Google Calendar Fix:

1. Remove Existing Google Account:

   • Open System Settings > Internet Accounts
   • Select your Google account
   • Click the "-" button to remove it
   • Confirm removal

2. Clear Google Calendar Cache:

   # Remove Google Calendar specific caches
   rm -rf ~/Library/Calendars/*@gmail.com*
   rm -rf ~/Library/Calendars/*@googlemail.com*

3. Re-add Google Account:

   • Go to System Settings > Internet Accounts
   • Click the "+" button
   • Select Google
   • Sign in with your Google credentials
   • Enable Calendars checkbox

4. Verify Calendar Access:

   • Open Calendar app
   • Go to Calendar > Settings > Accounts
   • Verify Google account shows "Calendars: On"
   • Press Cmd+R to refresh

Using App Passwords for Google:

If you have two-factor authentication enabled on Google:

1. Go to Google Account Security
2. Navigate to 2-Step Verification
3. Click App passwords at the bottom
4. Generate a new password for "Mail" on "Mac"
5. Use this password instead of your regular Google password

Microsoft Exchange and Outlook Integration

Enterprise users often encounter Exchange calendar issues after updating to macOS Tahoe.

Exchange Calendar Troubleshooting:

Problem: Exchange Calendar Not Syncing

1. Check Server Settings:

   • Open System Settings > Internet Accounts
   • Select your Exchange account
   • Verify server address is correct
   • Confirm username format ([email protected] or DOMAIN\username)

2. Reset Exchange Connection:

   • Disable Calendars for Exchange account
   • Quit Calendar app completely
   • Wait 30 seconds
   • Re-enable Calendars
   • Open Calendar and refresh

3. Modern Authentication Issues: Many organizations now require OAuth/Modern Authentication:

   • Remove the Exchange account
   • Re-add using Microsoft 365 option instead of Exchange
   • Sign in through the Microsoft authentication page
   • This ensures proper OAuth token handling

Problem: Out of Office Not Syncing

This is a known limitation - Calendar app doesn't display Exchange Out of Office status. Use Outlook or Microsoft Teams instead.

CalDAV Server Configuration

For users with CalDAV servers (Nextcloud, Synology, etc.):

Adding a CalDAV Account:

1. Open Calendar > Settings > Accounts
2. Click the "+" button
3. Select Other CalDAV Account
4. Enter:
   • Account Type: Manual
   • Username: Your CalDAV username
   • Password: Your CalDAV password
   • Server Address: Full CalDAV URL (e.g., https://nextcloud.example.com/remote.php/dav/)

Common CalDAV Issues:

Issue	Cause	Solution
Connection refused	Wrong port	Verify HTTPS (443) or HTTP (80)
Authentication failed	Incorrect URL format	Include full path to CalDAV endpoint
Partial sync	Permission issues	Check CalDAV account permissions
Slow sync	Large calendar	Enable calendar pagination on server

CalDAV Sync Optimization:

# Check CalDAV account status
plutil -p ~/Library/Preferences/com.apple.CalendarAgent.plist

# Force CalDAV resync
killall CalendarAgent
# Wait 10 seconds, then open Calendar

iCloud Family Sharing Calendar Issues

Family Sharing introduces additional complexity for calendar sync.

Problem: Shared Family Calendar Not Appearing

1. Verify Family Sharing is active:

   • System Settings > [Your Name] > Family Sharing
   • Confirm all members are listed

2. Check Calendar visibility:

   • Open Calendar
   • Look in sidebar under "Family" section
   • Ensure shared calendars have checkmarks

3. Refresh Family calendars:

   • Calendar > View > Refresh Calendar (Cmd+R)
   • Wait for sync to complete

Problem: Can't Edit Shared Calendar Events

This is often a permissions issue:

1. The calendar owner must grant edit access
2. Go to iCloud.com > Calendar
3. Click the Share icon on the shared calendar
4. Change permission from "View only" to "View & Edit"

Part 6: Advanced Troubleshooting Scenarios

Safe Mode Diagnostics

When standard troubleshooting fails, Safe Mode can help identify extension conflicts:

Boot into Safe Mode:

For Apple Silicon Macs (M1/M2/M3/M4):

1. Shut down your Mac completely
2. Press and hold the power button until "Loading startup options" appears
3. Select your startup disk
4. Press and hold Shift key
5. Click Continue in Safe Mode

For Intel Macs:

1. Restart your Mac
2. Immediately press and hold the Shift key
3. Release when login window appears
4. Log in (may take longer than normal)

Test Calendar in Safe Mode:

1. Open Calendar app
2. Check if sync works correctly
3. If it works in Safe Mode, a third-party extension is causing the issue
4. Restart normally and disable extensions one by one

Identifying Problematic Login Items

Login items can interfere with Calendar and Reminders:

1. Go to System Settings > General > Login Items & Extensions
2. Review the list of login items
3. Disable suspicious items one at a time
4. Restart and test Calendar after each change

Common Conflicting Apps:

• Menu bar calendar apps (Fantastical, BusyCal when running alongside Apple Calendar)
• VPN clients with aggressive filtering
• Security software intercepting network traffic
• Backup software accessing Calendar database

Network Diagnostics

Network issues often masquerade as Calendar problems:

Test Apple Server Connectivity:

# Check iCloud Calendar server
nc -vz caldav.icloud.com 443

# Check iCloud authentication server
nc -vz setup.icloud.com 443

# DNS resolution test
nslookup caldav.icloud.com

Expected Results:

• Connection should succeed on port 443
• DNS should resolve to valid IP addresses
• Response time should be under 200ms

Firewall Configuration:

If using a firewall, ensure these domains are allowed:

• *.icloud.com
• *.apple.com
• *.icloud-content.com
• *.push.apple.com

Migration and Upgrade Issues

If Calendar issues started after migrating to a new Mac or upgrading from an older macOS version:

Clean Calendar Migration:

Instead of using Migration Assistant for Calendar data:

1. On old Mac: Export calendars as .ics files

   • File > Export > Export...
   • Save each calendar separately

2. On new Mac: Fresh Calendar setup

   • Sign into iCloud (calendars will sync from cloud)
   • Import local calendars: File > Import...

3. Verify all events transferred correctly

Post-Upgrade Database Repair:

If you upgraded from macOS Sequoia or earlier:

# Backup and rebuild Calendar database
cd ~/Library/Calendars
cp -R . ../Calendars.backup.$(date +%Y%m%d)

# Remove cache and let it rebuild
rm -f "Calendar Cache"*
rm -rf ../Containers/com.apple.CalendarAgent/Data/Library/Calendars/*

# Restart Mac and open Calendar

Part 7: New Features in macOS Tahoe Calendar and Reminders

Calendar New Features

Despite the troubleshooting focus, macOS Tahoe 26 brings valuable improvements to Calendar:

Liquid Glass Design:

• Translucent, frosted glass aesthetic throughout the app
• New widget designs with dynamic backgrounds
• Improved dark mode appearance

Spotlight Integration:

• Create calendar events directly from Spotlight
• Type natural language like "Meeting with John tomorrow at 2pm"
• Press Enter to add event without opening Calendar

Apple Intelligence Features:

• Smart event suggestions based on emails and messages
• Automatic event creation from screenshots
• Improved natural language parsing

Quick Keys:

• Assign keyboard shortcuts for common actions
• Example: Set "ne" to create new event instantly

Reminders New Features

Liquid Glass Design:

• Consistent translucent UI with Calendar
• New list icons and color options
• Improved widget appearance

Apple Intelligence Integration:

• Auto-categorization of grocery lists
• Smart suggestions for reminder times
• Context-aware task recommendations

Timezone Support:

• Set individual reminder timezones
• Helpful for travel planning and remote work
• Automatic adjustment for daylight saving time

Enhanced Organization:

• Column view for better list management
• Improved drag-and-drop between lists
• New sorting options

Part 6: Calendar and Reminders Alternatives

When to Consider Alternatives

Consider third-party apps if you experience:

• Persistent sync failures despite troubleshooting
• Need for advanced features (natural language, integrations)
• Cross-platform requirements (Windows, Android)
• Enterprise features (meeting proposals, team calendars)
• Privacy concerns (end-to-end encryption)

Best Calendar Alternatives for macOS

Fantastical - Best for Design and Natural Language

• Price: $4.75/month (Flexibits Premium)
• Best For: Beautiful design, intuitive interface
• Key Features:
  • Superior natural language event creation
  • Built-in weather information
  • Meeting proposals
  • Available on macOS, iOS, Windows, Web
• Ideal When: You prioritize aesthetics and simplicity

BusyCal - Best for Power Users

• Price: $49.99 one-time purchase
• Best For: Maximum customization, professional use
• Key Features:
  • Advanced weather forecasts
  • Per-event notification customization
  • Full CalDAV support
  • Travel time calculations
• Ideal When: You need professional-grade features

Calendars by Readdle - Best Value

• Price: $19.99/year (PRO)
• Best For: Budget-conscious users, task management
• Key Features:
  • Natural language parsing
  • Video call integration (Zoom, Teams, Google Meet)
  • Extensive task support
  • All Apple devices included
• Ideal When: You need tasks + calendar, best value

Best Reminders Alternatives for macOS

Things 3 - Best for GTD Workflow

• Price: $49.99 (Mac), $9.99 (iPhone)
• Best For: Getting Things Done methodology
• Key Features:
  • Beautiful, focused design
  • Headings and checklists
  • Quick Entry from anywhere
  • Apple Watch support
• Ideal When: You follow GTD or want elegant simplicity

Todoist - Best for Cross-Platform

• Price: Free tier available, $4/month Pro
• Best For: Cross-platform teams
• Key Features:
  • Available everywhere (Mac, Windows, Android, Web)
  • Team collaboration features
  • Natural language input
  • Extensive integrations
• Ideal When: You work across multiple platforms

OmniFocus - Best for Complex Projects

• Price: $49.99/year subscription
• Best For: Project management, complex workflows
• Key Features:
  • Powerful project organization
  • Custom perspectives
  • Review feature
  • Professional-grade filtering
• Ideal When: You manage complex, multi-step projects

Use Native Apps vs Alternatives

Stay with Apple Calendar/Reminders if:

• You use exclusively Apple devices
• You want zero configuration
• You prefer built-in iCloud integration
• You don't need advanced features
• You want Siri and system integration

Switch to Alternatives if:

• You need cross-platform support (Windows, Android)
• You want advanced natural language input
• You need team collaboration features
• You require enterprise integrations
• You prefer one-time purchase over subscriptions
• You need advanced CalDAV support

Part 7: Prevention and Best Practices

Preventing Future Sync Issues

Keep macOS Updated:

• Install updates promptly (they often fix sync bugs)
• Read release notes for known issues
• Consider waiting a week after major updates

Regular Maintenance:

• Restart your Mac weekly
• Clear browser caches monthly
• Monitor Activity Monitor for unusual processes

Backup Strategy:

• Export Calendar archive monthly
• Enable iCloud backup on all devices
• Consider third-party backup solutions

Optimal Calendar and Reminders Settings

For Best Sync Performance:

1. Set iCloud calendar as default
2. Enable automatic date/time
3. Disable unnecessary Siri suggestions
4. Use consistent Apple ID across all devices
5. Ensure adequate iCloud storage

For Best Battery Life:

1. Disable background app refresh for Calendar (if not needed)
2. Reduce sync frequency for non-critical accounts
3. Use manual refresh instead of automatic for some accounts

Monitoring Calendar Health

Weekly Health Check:

1. Open Calendar, press Cmd+R to refresh
2. Check Activity Monitor for CalendarAgent CPU usage
3. Verify events appear on all devices
4. Test creating a new event and confirm it syncs

Monthly Maintenance:

1. Delete old completed reminders (older than 6 months)
2. Remove outdated calendar subscriptions
3. Review and remove unused calendar accounts
4. Clear Calendar cache if experiencing slowdowns

Frequently Asked Questions (FAQ)

Calendar FAQ

Q: Why did my Calendar events disappear after updating to macOS Tahoe?

A: This is usually caused by not accepting the new iCloud Terms and Conditions. Go to System Settings > [Your Name] > iCloud and look for a Terms and Conditions prompt. Accept the terms, then refresh Calendar with Cmd+R. Your events should reappear within a few minutes.

Q: Can I use Apple Calendar and Google Calendar together?

A: Yes, you can add multiple calendar accounts. Go to System Settings > Internet Accounts, add your Google account, and enable the Calendars checkbox. Both iCloud and Google calendars will appear in the Calendar app sidebar.

Q: How do I prevent duplicate events when using multiple calendar accounts?

A: Duplicates often occur when the same calendar is syncing through multiple sources. For example, if you have a Google calendar syncing via both Internet Accounts and CalDAV, remove one connection. Also, set a single default calendar in Calendar > Settings > General to avoid creating events in multiple places.

Q: Why does CalendarAgent use so much CPU?

A: High CalendarAgent CPU usage is typically caused by: corrupted cache files, large numbers of old completed Reminders, Siri calendar suggestions processing, or sync conflicts. Try clearing the cache, deleting old completed Reminders, and disabling Siri suggestions for Calendar.

Q: How often does Calendar sync with iCloud?

A: Calendar syncs with iCloud using push notifications for real-time updates. When you create or modify an event, it should appear on other devices within seconds. If sync seems delayed, force a refresh with Cmd+R or check your network connection.

Reminders FAQ

Q: Why are my Reminders showing on iPhone but not on Mac?

A: This usually indicates an iCloud sync issue on the Mac side. Go to System Settings > [Your Name] > iCloud and toggle Reminders off then on. If that doesn't work, try signing out and back into iCloud. Ensure both devices are using the same Apple ID.

Q: Can I move Reminders between lists?

A: Yes, simply drag and drop a reminder from one list to another in the sidebar. You can also right-click a reminder and select "Move to List" to choose a destination. In macOS Tahoe 26, you can also use the new Column view for easier list management.

Q: How do I recover deleted Reminders?

A: Unfortunately, Reminders doesn't have a built-in trash or recovery feature. Your best options are: restore from an iCloud backup, check the "Completed" section (in case the reminder was marked complete instead of deleted), or use Time Machine to restore the Reminders database from ~/Library/Reminders/.

Q: Why do characters get skipped when I type quickly in Reminders?

A: This is a known bug in macOS Tahoe 26 affecting the Scheduled view. The animation causes input lag when typing quickly. Workarounds include typing slower, using a different view (Today or Lists), or creating reminders via Spotlight or Siri instead.

Q: Can I share Reminders lists with non-Apple users?

A: No, Reminders lists can only be shared with other iCloud users. For cross-platform task sharing, consider using third-party apps like Todoist, Microsoft To Do, or Google Tasks that work across Apple, Android, and Windows devices.

Sync and iCloud FAQ

Q: What's the difference between "On My Mac" and iCloud calendars?

A: "On My Mac" calendars are stored locally and don't sync to other devices. iCloud calendars sync across all your Apple devices. For most users, iCloud calendars are recommended. Local calendars are useful for device-specific scheduling or sensitive information you don't want in the cloud.

Q: How much iCloud storage do Calendar and Reminders use?

A: Calendar and Reminders data typically uses very little iCloud storage - usually less than 100MB even with thousands of events. However, if iCloud storage is completely full, sync will fail. Free up space by managing Photos, iCloud Drive, or device backups.

Q: Can I access my Calendar offline?

A: Yes, Calendar caches your events locally. You can view and create events while offline, and they'll sync when you reconnect to the internet. However, changes made on other devices while offline won't appear until you're back online.

Q: Why does my Calendar show a different timezone?

A: Go to Calendar > Settings > Advanced and check the timezone settings. Ensure "Turn on time zone support" is configured correctly for your location. Also verify your Mac's timezone in System Settings > General > Date & Time matches your actual location.

Troubleshooting Flowchart

Calendar/Reminders Not Working?
│
├─ Getting Error 9 (kEKAccountErrorDomain)?
│  └─ Accept iCloud Terms in System Settings > [Your Name] > iCloud
│
├─ Events/Reminders Not Syncing?
│  ├─ Toggle Calendar/Reminders off/on in iCloud settings
│  ├─ If still broken: Clear cache files + restart
│  └─ Last resort: Sign out/in to iCloud completely
│
├─ Events/Reminders Not Appearing?
│  ├─ Check calendar/list is enabled (has checkmark)
│  ├─ View > Refresh (Cmd+R)
│  ├─ Check internet connection
│  └─ Verify timezone settings are correct
│
├─ App Freezing or Crashing?
│  ├─ Force quit app and related processes
│  ├─ Delete cache files
│  └─ Restart computer, reopen app
│
├─ High CPU Usage (CalendarAgent)?
│  ├─ Delete old completed Reminders
│  ├─ Disable Siri calendar suggestions
│  └─ Clear cache files, restart
│
└─ Still Broken After All Steps?
   ├─ Complete iCloud sign-out/sign-in
   ├─ If still failing: Consider third-party alternatives
   └─ Contact Apple Support for hardware-related issues

Conclusion: Mastering Calendar and Reminders on macOS Tahoe

macOS Tahoe 26's Calendar and Reminders apps offer powerful productivity features when working correctly. While sync issues and bugs can be frustrating, most problems have straightforward solutions that don't require advanced technical knowledge.

Key Takeaways:

1. Accept New Terms: The kEKAccountErrorDomain Error 9 is almost always fixed by accepting new iCloud Terms and Conditions
2. Toggle Sync: Most sync issues resolve by toggling Calendar/Reminders off and on in iCloud settings
3. Clear Cache: Persistent issues often require clearing cache files and restarting
4. Keep Updated: Many bugs are fixed in subsequent macOS updates
5. Know When to Switch: If native apps consistently fail, quality alternatives exist

Recommended Next Steps:

• If experiencing performance issues, see our macOS Tahoe Performance Analysis
• For broader sync problems, check our Continuity & Sync Troubleshooting Guide
• For Terminal command help, visit our Terminal Complete Guide
• For Notes app issues, see our Notes App Complete Guide
• Verify your Mac's compatibility with our Compatibility Guide

Having persistent issues not covered in this guide? Check Apple's official Calendar troubleshooting page or contact Apple Support for hardware-related problems.