Why is the first Microsoft Graph sync taking so long?

A first Microsoft Graph sync can take much longer than later syncs when an Outlook or Microsoft 365 account has thousands of events, many years of history, or several calendars.

Why can it look stalled?

Microsoft Graph controls how the initial event list is split into pages. BusyCal then retrieves the full details in batches of up to 20 events. Microsoft may also slow requests temporarily when a large amount of data is being downloaded.

Events are not guaranteed to arrive in date order. Recent events may appear before older ones, or the other way around, so a calendar can look incomplete while BusyCal continues to show Syncing.

How long should it take?

Large accounts can take several hours to finish, and a calendar with thousands of events may need to sync overnight. The exact time depends on the number of calendars and events, the network connection, and Microsoft’s server load and rate limits.

Once the first sync is complete, later syncs are usually much faster because BusyCal retrieves only changes.

What should I do?

• On Mac, leave BusyCal open and keep the Mac awake with a reliable internet connection.
• On iPhone or iPad, connect the device to power and Wi-Fi and leave BusyCal open in the foreground. iOS limits how long apps can work in the background.
• Do not force-quit BusyCal or remove and re-add the account while the first sync is still making progress. Re-adding the account starts the initial sync again.
• Each device completes its own first sync. Finishing on a Mac does not make an iPhone or iPad download the same data from the Mac.

If you do not need all of your old calendar history, archive or delete old events in Outlook before starting the account again in BusyCal. This reduces the amount of data Microsoft Graph must send.

If the account still shows Syncing after an uninterrupted overnight run, or BusyCal reports an error, please contact BusyCal Support.