What Is an ICS File?
A Beginner's Guide to Calendar Sharing

Last updated: 2026-03-18

An ICS (iCalendar) file is a standard format for sharing calendar events between apps. The same .ics format works across Google Calendar, Microsoft Outlook, Apple Calendar, and virtually every calendar application. When you "subscribe" to an ICS URL, events from another calendar appear in your app and update automatically.

What does an ICS file look like?

It's a plain text file containing event data:

BEGIN:VCALENDAR
VERSION:2.0
BEGIN:VEVENT
SUMMARY:Team Meeting
DTSTART:20260320T100000Z
DTEND:20260320T110000Z
LOCATION:Conference Room A
END:VEVENT
END:VCALENDAR

ICS file vs. ICS URL — what's the difference?

ICS file: A one-time import. Used for email invitations (.ics attachments). Changes aren't synced.

ICS URL (subscription): Your calendar app periodically fetches the URL to get the latest events. Changes sync automatically.

How to get your ICS URL

Google Calendar

Open Google Calendar Settings
Click on the calendar you want to share
Scroll to "Integrate calendar"
Copy the "Secret address in iCal format"

Microsoft Outlook (Microsoft 365)

Go to outlook.office.com
Settings → "View all Outlook settings"
"Calendar" → "Shared calendars"
Select a calendar → Publish and copy the ICS link

Apple iCloud Calendar

Open Calendar on iCloud.com
Click the share icon next to a calendar
Enable "Public Calendar"
Copy the displayed URL

How to subscribe to an ICS URL

Google Calendar: "Other calendars" → "+" → "From URL"
Apple Calendar: File → "New Calendar Subscription" → paste URL
Outlook: "Add Calendar" → "From Internet" → paste URL

Privacy warning: what's exposed in an ICS URL?

ICS URLs have no authentication. Anyone with the URL can see all event details — titles, locations, descriptions, and attendee email addresses. If you only want to share your availability (free/busy), use a filtering service like SafeCal.

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FAQ

What is an ICS file?

An ICS (iCalendar) file is a standard format (.ics) for storing and sharing calendar events. It works across all major calendar apps including Google Calendar, Outlook, and Apple Calendar.

What is the difference between an ICS file and an ICS URL?

An ICS file is a one-time import (e.g., email invitation attachments). An ICS URL is a subscription — your calendar app periodically fetches it to get the latest events, and changes sync automatically.

Is it safe to share my ICS URL with others?

ICS URLs contain all event details (titles, locations, descriptions, attendee emails) and have no authentication. Anyone with the URL can access everything. Use a filtering proxy like SafeCal to share only your availability.

→ Your Google Calendar ICS Link Is Leaking Private Data → 複数のカレンダーを1つのURLに統合する方法

What Is an ICS File?A Beginner's Guide to Calendar Sharing