The ICS File Format: Creating Calendar Events That Work Everywhere

The ICS (iCalendar) format is a text-based standard for calendar events that every major calendar application supports: Google Calendar, Apple Calendar, Outlook, Thunderbird. When you click "Add to Calendar" on a website, you are downloading an .ics file. Understanding the format lets you programmatically generate calendar events for your applications. The format An ICS file is plain text with a specific structure: BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Your App//EN BEGIN:VEVENT DTSTART:20260401T090000Z DTEND:20260401T100000Z SUMMARY:Team Standup DESCRIPTION:Daily team sync meeting LOCATION:Conference Room B STATUS:CONFIRMED UID:unique-id-12345@yourdomain.com END:VEVENT END:VCALENDAR Each event is a VEVENT block inside a VCALENDAR container. The required fields are DTSTART , SUMMARY , and UID . Everything else is optional but useful. Date-time formats ICS supports several date-time formats: UTC (recommended): End with Z DTSTART:20260401T090000Z Local time with timezone: DTSTART;TZID=Ame