CorrectICS

Common ICS import errors by calendar app (Google, Outlook, Apple)

ICS import problems look similar (“won’t import”, “invalid iCalendar”, “wrong time”), but the root cause often depends on the calendar app.

Fastest path:

If you’re new to ICS, start with: What is an ICS file?.

Google Calendar (web)

Common failures:

  • invalid/missing BEGIN:VCALENDAR / END:VCALENDAR
  • malformed lines or invalid characters
  • broken line folding (long lines split incorrectly)
  • recurrence rules that are syntactically invalid (RRULE)

Next steps:

Outlook (Desktop, Exchange, Office 365)

Common failures:

  • timezone issues (local times with TZID + missing/bad VTIMEZONE)
  • TZID values that aren’t valid IANA zones (EST, PST, Eastern Standard Time)
  • recurrence + exceptions (RRULE / RECURRENCE-ID) inconsistencies

If your symptom is “one hour off” or “DST drift”, start here: Fix ICS timezone errors (events at the wrong time).

For the deeper technical explanation: Fix ICS Time Zone Errors (TZID/VTIMEZONE).

Apple Calendar (macOS / iOS)

Common failures:

  • imports succeed but events show incorrect time zone labeling
  • recurrence edge cases (especially with time zones)
  • malformed lines/encoding issues (less common, but still possible)

If you’re troubleshooting an attachment: How to open an ICS file and add it to your calendar.

Checklist for developers (best practices)

If you generate ICS files:

  • validate every output in CI
  • keep UID stable
  • choose UTC (Z) when possible; otherwise use valid IANA TZIDs
  • include VTIMEZONE when you need Outlook Desktop/Exchange compatibility

See: My .ics file won’t import — quick checklist for developers and Generate Correct ICS Files (Best Practices + Templates).

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