BusyCal not working: what to check, in order

When BusyCal stops behaving, the symptom rarely points at the cause. A calendar that will not sync can be a clock problem. Duplicate events can be a Reminders format problem. An iPhone that shows nothing can be working exactly as designed. The fastest way through is to check layers in a fixed order, starting with the cheapest checks and leaving anything destructive for last.

The order below follows BusyCal's own documentation. Each step either clears a whole category of causes or tells you which step to jump to.

Start with the symptom

Symptom	Check first	Likely layer
Google or iCloud sign-in keeps failing	Mac date and time settings	System
Sync stopped after a macOS upgrade	BusyCal version and license window	App version
Office 365 or Exchange stopped syncing	Account type in BusyCal settings	Service change
The same event appears twice	Invitations on two accounts, Reminders format	Data source
Events missing on iPhone	Where the calendar is hosted	Storage location
Old emails appear as overdue tasks	Microsoft Flagged Emails list	Service behavior
App will not open, "not in the correct format"	Backups, then reset	Local database
Events cannot be edited, invitations cannot be answered	Whether the account is connected through Apple Calendar	Connection type
Calendars vanished on a new Mac	Accounts under Settings, Accounts	Setup

Most problems sit in the first four rows, and none of those require deleting anything.

Step 1: the clock

It sounds too simple, but BusyCal's documentation puts it first for a reason.

Google authentication will fail if your system time is incorrect. Source: busymac.com

The iCloud guide carries a similar warning: if the Mac is not set to update the date and time automatically, the app-specific password can fail without any obvious reason. Open System Settings, go to General, then Date & Time, and confirm that setting the time automatically is on. Macs that were set manually for testing, or that drifted after sleeping through a time zone change, are common offenders.

This takes under a minute and rules out an entire class of authentication errors. Do it before touching any account.

Step 2: the credentials

BusyCal does not borrow accounts from macOS System Settings. Every account is stored separately under BusyCal, Settings, Accounts, so that is where to look.

Google. The sign-in flow presents a long list of permissions. BusyCal's documentation states that every permission must be selected, and that unchecking any of them breaks sync. If there is any doubt about what was granted, remove the account and add it again, choosing Select all.

iCloud. Third-party apps connect with an app-specific password, not the Apple Account password. Sign in with the primary iCloud address, because aliases are rejected. If the account uses an @mac.com address, the documentation recommends using the @icloud.com form instead. App-specific passwords can be reused across devices, so storing one securely saves a step on the next Mac.

Microsoft 365. If the sign-in asks for admin consent, the connection cannot complete until an administrator in the organization approves it. No setting on the Mac changes that.

BusyCal's FAQ index also lists recurring sign-in topics, including Zoom repeatedly asking to be reauthorized and Yahoo reporting an incorrect password. If the service in question is one of these, the matching FAQ entry is the next stop.

Step 3: the version and the calendar year

A setup that worked for months and then stopped usually means something changed outside the app.

License window. A direct BusyCal license includes 18 months of updates. After that, the installed version keeps running, but it does not receive fixes. The developer's licensing page says plainly that macOS updates and changes at iCloud, Google, and Exchange can break older versions, and that renewing is how compatibility fixes arrive. Check BusyCal's version and when the update window ends. If a macOS upgrade happened after that date, the version is a real suspect.

The Exchange deadline. BusyCal moved Office 365 syncing to Microsoft Graph. Its documentation notes that Microsoft begins blocking Exchange Web Services on Exchange Online on October 1, 2026, with full shutdown on April 1, 2027. An account added long ago as "Exchange" or legacy "Office 365" uses the old path. In Settings, Accounts, add the account again with the server type Office 365 (Microsoft Graph).

Leftover flagged emails. After switching to the Graph connection, Microsoft may add a Flagged Emails task list. Older flagged messages that were never completed then show up as overdue tasks. This is not corruption. The list can be hidden in BusyCal without changing anything in Outlook.

Step 4: duplicates and missing events

Duplicates from two sources. A meeting invitation landing on both a work and a personal account, or two similar holiday subscriptions, will show the same event twice. BusyCal's View menu has Combine Identical Events. Two events count as identical when both are events rather than tasks, the titles match, the start and end times match, and they sit on different calendars. The combined view shows one copy, preferring a writable calendar, and fires one alarm. Nothing is deleted, and the hidden copy is reachable from the Info Panel.

Duplicates from Reminders. If a yellow warning triangle appears next to Reminders lists, the Reminders storage format differs between devices. Reminders upgraded on macOS Catalina or iOS 13 and later no longer sync through iCloud's CalDAV server, so the same list can appear once under Reminders and once under the iCloud account, with no sync between them. The documentation recommends picking one path and stopping use of the other.

Missing on iPhone. BusyCal reaches iOS only through a server. A calendar stored "On My Mac" will never appear on a phone. Shared Google calendars also need to be selected in Google's sync settings before the built-in iOS Calendar shows them. For tasks synced through Google, only the title, due date, and notes travel. Due time, recurrence, alarms, and priority stay between BusyCal clients.

Blocking copies that revert. Events mirrored to another calendar are refreshed from the original on the Mac that created them. Editing the copy directly is pointless, because the next change to the original overwrites it.

Edits by other people go unnoticed. On shared calendars, changes made by others arrive through sync without drawing attention. In each calendar's info dialog, the option to show change notifications in the Inbox adds a badge and a message whenever someone adds or changes an event. Under Settings, Advanced, BusyCal can also ask for confirmation before editing or deleting an event on a shared calendar, which prevents accidental changes that then look like sync errors to everyone else.

A related case: events that are read-only

Since version 2024.1.2, BusyCal can read calendars through the Apple Calendar app. The documentation describes this as a workaround for cases where an account cannot be added directly, such as some enterprise setups, and lists its limits: events are read-only, meeting invitations cannot be accepted or declined, and many BusyCal features do not apply to those events.

If events refuse to be edited or invitations offer no response buttons, open Settings, Accounts, and look at how the calendar is connected. If it arrives through Apple Calendar, add the underlying account (iCloud, Google, or Exchange) directly to BusyCal instead. Having both connections active at once is also a common source of duplicates, so remove the Apple Calendar connection once the direct account is working.

The reason for the limit is technical. Apple's EventKit framework, which third-party apps use to read Apple Calendar data, does not support many of BusyCal's features, including attendee management, custom alarms, travel time, tags, and cross-calendar blocking.

Step 5: when the app will not open

If BusyCal reports that its file cannot be opened because it is not in the correct format, the local database is likely corrupted. The fix is a reset, which is destructive, so confirm backups first. By default BusyCal backs up every 24 hours and keeps the last ten, inside its container folder in the user Library. The backup location and schedule can be changed under Settings, Backup.

To reset, hold Option while opening BusyCal and choose Reset BusyCal in the Startup Options dialog. The reset disconnects cloud accounts, deletes the database, and quits. Calendars hosted on iCloud or Google return once the accounts are added again. Local calendars need restoring from a backup.

If the Startup Options dialog never appears, the documentation describes a manual reset: delete the files beginning with BusyCal.bsql inside the app's Application Support folder, relaunch, and re-enter accounts. iCloud users will need an app-specific password again.

For recovering a few events rather than a whole calendar, restore the backup as an "On My Mac" calendar, drag the missing events to their proper calendar, then delete the restored copy. Restoring an entire calendar replaces everything created after the backup date.

After moving to a new Mac

A fresh Mac is a frequent source of reports that BusyCal has lost every calendar. In most cases nothing is lost. The data is still on the server, and the new installation simply has not been told where to find it.

According to BusyCal's backup documentation, nearly all BusyCal settings sync between Macs over iCloud. Signing in with the same Apple Account and installing BusyCal restores the settings. Calendar accounts are a separate matter. They are not copied automatically, so the calendars stay empty until each account is added again.

Under Settings, Accounts, a new Mac may already list accounts used on another device. Clicking Use Account and re-entering credentials reconnects them. If the list is empty, add accounts with the plus button. iCloud needs the app-specific password again, and an existing one can be reused if it was stored somewhere safe.

What does not come across is anything local. Calendars stored "On My Mac" live only on the old machine. Before retiring it, export those calendars as .ics files, or copy the most recent BusyCal backup and restore it on the new Mac. A license also needs attention: a personal direct license activates on up to five Macs, so retiring an old machine and adding a new one normally fits within the limit, and a lost registration code can be looked up on the developer's site.

Step 6: before writing to support

BusyCal's help page offers a button that creates an email with log files attached, addressed to the support team. Add a description of the problem in the message body. Support hours are Monday to Friday, 10am to 6pm GMT, with shorter weekend and holiday hours, and replies can take 36 to 48 hours.

Include the BusyCal version, the macOS version, the account type involved, when the problem started, and which of the steps above were already tried. That usually saves a round of back and forth.

What to change first

Check the Mac's clock and each account's credentials before anything else. Those two steps resolve most sync failures and cost nothing. Once the calendar is stable again, look at the time that still goes missing in a busy week, which tends to be entering events and planning travel between them. The travel time guide and the FAQ cover how Caltimate handles that part.