Three account routes
Apple-managed calendars arrive through the system calendar store. This includes iCloud and other accounts already configured for Apple Calendar. Google, Microsoft 365, iCloud, CalDAV, WebDAV, calendar subscriptions and Todoist can also connect directly under Settings → Accounts.
You can use the sources together. InstaCal groups calendars by account and provider and attempts to de-duplicate the same event when it is visible through more than one route.
Browsing is local
Every directly connected account keeps a local mirror of about six years of events — two years back and four years ahead — on the device. Any month in that span paints the moment you arrive, whether you are online or not, because nothing has to be fetched first to draw it.
The mirror is kept up to date by asking each provider only for what has changed since the last check, so an ordinary refresh moves very little data. Each calendar is also reconciled in full on a rolling weekly cadence, spread out so an account’s calendars do not all fall due at once, and the weeks either side of today get a hygiene pass roughly once a day.
Refresh behavior
System calendars refresh through Apple’s calendar framework. Direct accounts use provider APIs and incremental sync. On Mac, Settings → Accounts → Refresh → Refresh accounts every controls the normal interval; manual refresh remains available when you need the newest state immediately.
Reminders you create with Siri, or in Apple’s Reminders app, no longer wait for the next account sync: on Mac they appear as soon as InstaCal notices the change, and on iPhone and iPad they are there when you return to the app.
Subscribed calendars follow their own Refresh interval, chosen when you add them.
Offline and cached events
Direct accounts retain a local event cache so a temporary network failure does not empty the calendar. Accounts labels the connection Offline while showing the last known data. Changes that require the provider wait until connectivity returns.
A calendar that stops appearing in an account is not thrown away immediately. InstaCal hides it but keeps its events for about a week, so a calendar that briefly disappears — unshared and reshared, or a provider hiccup — comes back complete instead of being downloaded again.
Move an event to another calendar
Choose Move Calendar from an event’s action menu and the event re-files immediately: it leaves the old calendar and appears under the new one on the spot, and it stays there through the next refresh.
A move you make somewhere else — Google’s web calendar, another device — is noticed and repaired within a refresh, so the event stops showing under both calendars. Moving between two different account types is a copy followed by a delete; if the delete fails, InstaCal tells you the event now exists on both calendars and asks you to remove the old one by hand.
Rate limits and retries
A Google or Microsoft rate limit, or a passing server error, is not a failure: InstaCal retries with the wait the service itself asks for, and an account’s calendars are read in full however many there are. Editing an event keeps a Teams meeting’s join link, and your reply to an invitation leaves the other guests’ replies intact.
Sign-in needed
If a provider expires or rejects authorization, the account shows Sign-in Needed. Open it under Settings → Accounts and reconnect. Removing and re-adding should be a later step because it discards the local cache and account-specific choices.
Avoid duplicate account paths
If the same Google or Microsoft calendar is both enabled in Apple Calendar and connected directly, compare the account labels in Settings → Calendars. Hide one copy when de-duplication cannot prove that two differently identified items are the same.
A calendar shared between two of your own connected Google accounts is a different case and is not a duplicate to hide: it is listed under both accounts because each account really can see it, and the account that can write to it owns your edits.
