Mac Calendar not syncing: the checks that find the stuck account

An event created on the iPhone does not show up on the Mac. Or the Mac shows last week's version of a shared work calendar while everyone else sees the current one. The instinct is to quit and reopen Calendar, then restart the Mac, then start searching for a fix to "Mac Calendar sync." That order wastes the most time, because Mac Calendar is not one syncing system. It is a window onto several independent accounts, each with its own connection, its own refresh setting, and its own way of failing. Almost every case is one account being stuck while the others work normally.

The useful first move is to find out which one.

Establish whether it is the app or the account

Before changing any setting, check the same calendar somewhere else. Open iCloud.com for an iCloud calendar, Google Calendar in a browser for a Google account, or Outlook on the web for an Exchange account. Look for the event that is missing.

There are two outcomes, and they lead to very different investigations. If the event is there on the web but not on the Mac, the data exists and the Mac is not receiving it, and everything below applies. If the event is missing on the web too, then the Mac never sent it, or the device that created it never sent it, and the place to start is the device where the event was created rather than the Mac.

This one check removes most of the guessing. It also settles the common case where an event was created into the wrong calendar rather than lost, since the web view shows which calendar it actually landed in.

While there, look at Apple's system status page if the account is iCloud. An outage on the provider's side produces exactly the symptoms of a broken local setup, and no amount of local fixing will help until it clears.

Look for the warning symbol, because it names the account

Mac Calendar signals a failed connection in the calendar list. Apple's documentation is explicit about what it means.

If you see a warning symbol next to a calendar you published, shared, or subscribed to, Calendar is unable to connect to the calendar account. Check your internet connection and try refreshing or updating the calendar again. Also, make sure the calendar hasn't been deleted or moved. Source: support.apple.com

If the calendar list is hidden, choose View and then Show Calendar List. A symbol next to one calendar, with the others clean, is the answer to "which account" in a single glance. For a subscribed calendar, Control-click its name and choose Get Info to see the web address it is pointing at. A subscription whose source URL has moved or been deleted will fail forever without ever producing an error dialog.

This is also where a misread happens. A calendar with no events might simply be unticked. An unticked calendar is hidden, not broken, and no amount of account work will bring it back. Confirm the checkbox before treating it as a sync fault.

Check the refresh setting, which is per account

Mac Calendar does not poll every account on the same schedule. Each account has its own setting, and a manual setting looks exactly like a broken connection.

Go to Calendar, then Settings, then Accounts. Select the account, click the Refresh Calendars pop-up menu, and look at what is selected. Push is the setting that behaves the way most people assume the app already behaves.

If you choose Push, the account is updated automatically when you make a change on any of your devices that use the same account, or when someone makes a change to a shared calendar in that account. Source: support.apple.com

Subscribed calendars are separate again. Control-click the calendar name, choose Get Info, and set the Auto-refresh pop-up menu. A subscription left at a long interval, or at no automatic refresh at all, will sit stale indefinitely.

For a forced check right now, choose View and then Refresh Calendars. If the missing event appears immediately after a manual refresh, the data path is fine and the problem is the schedule, not the connection. That is a two-second test that rules out an entire category of causes.

The credential that expired without saying so

An account that worked for months and then stopped, with no setting changed, usually means credentials rather than configuration. There is one specific trap on macOS that produces this exact pattern.

When a non-Apple app signs in to an Apple Account to reach iCloud mail, contacts, or calendars, it uses an app-specific password. Those passwords are revoked automatically whenever the main Apple Account password is changed or reset.

Any time you change or reset your primary Apple Account password, all of your app-specific passwords are revoked automatically to protect the security of your account. You need to generate new app-specific passwords for any apps that you want to continue using. Source: support.apple.com

Up to 25 app-specific passwords can be active at once, and they are managed in the Sign-In and Security section at account.apple.com. So a routine password change on a phone, weeks earlier, quietly stops calendar sync in a third-party client. Nothing on the Mac announces the cause.

The same shape applies elsewhere. A Google account whose access was revoked, or a work account behind a policy that expires tokens, fails silently in the same way. The tell is always the same: it used to work, nothing was changed locally, and one account is affected while the rest are fine. Removing and re-adding that single account is the fix, and it is safe for a server-based account because the data lives on the provider's side.

CalDAV accounts, where the settings are entered by hand

Accounts added through a provider on Apple's list configure themselves. Accounts added as Other CalDAV are a different situation, because the connection details were typed in by a person and can therefore be wrong in ways that produce intermittent rather than total failure.

Mac Calendar offers three levels when adding one. Automatic asks only for an email address and password. Manual asks for a user name, a password, and the server address. Advanced asks for the user name, password, server address, server path, and port number, and adds checkboxes for SSL and Kerberos v5 authentication.

The failure mode that wastes the most time here is a wrong server path or port combined with a server that answers anyway. The account appears connected, some calendars appear, and writes silently fail or land somewhere unexpected. When a self-hosted or provider-specific CalDAV account misbehaves, the fastest route is to open the account in Settings and compare every field against the provider's current documentation rather than adjusting one value at a time. Providers change the recommended host and path more often than people expect, and a setting entered correctly two years ago can be wrong now.

Adding a calendar is worth separating from adding an account, too. If a new calendar cannot be created inside a particular account on the Mac, Apple's guidance is to create it on the provider's website instead, then let it appear. A failure at that step is a permission issue on the account, not a sync issue in the app.

When the Mac is the one that is ahead

The reverse direction gets less attention and has its own causes. Events created on the Mac that never reach other devices usually land in a calendar that does not sync at all.

Calendars listed under On My Mac are local. They exist on that computer, they are not backed by any server, and nothing carries them to a phone. An event typed quickly while a different calendar happened to be selected will sit there, correct and invisible everywhere else. The Mac Calendar setting that decides where new events go is the default calendar, and it is worth setting deliberately to a server-based calendar rather than leaving it wherever it ended up.

The other cause is a published calendar with automatic publishing switched off. For calendars under On My Mac that are published, Control-click the calendar, choose Get Info, and confirm that "Publish changes automatically" is selected. Without it, changes stay local until published by hand, which looks identical to a sync failure to anyone subscribed on the other end.

When it is an Exchange limit rather than a fault

Exchange accounts have a documented behavior that is regularly reported as a sync bug. It is a limit, and knowing it saves hours.

In an Exchange account there is one main calendar, named Calendar. Additional calendars can be created inside that account, but they do not get the full feature set. Apple states that in those additional calendars, updated invitations and attendee responses will not be visible, the events will not be visible to delegates who share the calendar account, and they will not appear when other people check availability.

So a team that organizes work into several calendars inside one Exchange account will see invitation responses stop updating, and colleagues will book over blocked time because that time is invisible to a free-busy lookup. Full calendar features are available only in the main Exchange calendar. The fix is structural: keep anything that involves invitations, delegates, or availability in the main calendar.

Delegate calendars are worth checking separately as well, because a calendar shared through delegation behaves differently from a calendar shared directly, and tools that read Mac Calendar may not see it at all.

An order of checks that finds it fastest

Running these in order avoids the trap of changing five things at once and learning nothing.

Step	Check	What it rules out
1	Same calendar on the web	Whether data exists at all
2	Calendar checkbox ticked	Hidden calendar mistaken for missing events
3	Warning symbol in the calendar list	Which account is failing
4	View then Refresh Calendars	Schedule versus connection
5	Refresh Calendars setting per account	Manual or long interval
6	Credentials for the one failing account	Expired or revoked access
7	Exchange main calendar versus extra calendars	A limit rather than a fault

Two things deliberately do not appear on that list. Restarting the Mac is not a diagnostic step, because it fixes nothing the steps above do not fix, and it hides the cause so the problem returns. Deleting the Calendar app's local data is a last resort, not a second step, and it should never be tried on an account whose only copy of the data is local, meaning the calendars sitting under On My Mac.

What to change first

Start at step 1 and stop at the first step that gives a clear answer, then fix only that account. If the checks come back clean and the real complaint is that the week is unmanageable rather than out of date, the change belongs in how events get entered and how travel is reserved, which is what Caltimate is built around. The mechanics are described under entering events and travel time, and the FAQ covers which accounts are supported.