Back to glossary

July 10, 2026

What is an ICS file?

Learn what an ICS file is, how it works, and why it's the universal standard for sharing calendar events.

What is an .ics file?

An ICS file (which uses the .ics file extension) is a universal calendar format used by several email and calendar programs, including Microsoft Outlook, Google Calendar, and Apple Calendar.

It allows users to share calendar events across different programs seamlessly.

How does it work?

An ICS file is essentially a plain text file that contains structured data following the iCalendar standard (RFC 5545).

Here is what the inside of a simple ICS file looks like:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Invitly//EN
BEGIN:VEVENT
UID:123456789
DTSTAMP:20260710T120000Z
DTSTART:20260715T150000Z
DTEND:20260715T160000Z
SUMMARY:Product Launch Webinar
DESCRIPTION:Join us for the Q3 product launch!
LOCATION:https://zoom.us/j/123456
END:VEVENT
END:VCALENDAR

Why is it important?

If you are hosting an event, sending an ICS file or providing an "Add to Apple Calendar" link (which downloads an ICS file on iOS/macOS) is the most reliable way to ensure your attendees block out their schedule.

Invitly automatically generates and hosts perfectly formatted ICS files for every event you create.