Components and the shape of an event
An iCalendar file opens with BEGIN:VCALENDAR and contains one or more components: VEVENT for appointments, VTODO for tasks, VJOURNAL for notes and VFREEBUSY for availability. A typical VEVENT carries DTSTART and DTEND timestamps, a SUMMARY, an optional LOCATION and DESCRIPTION, and a UID that uniquely identifies it so updates can replace the original rather than duplicate it. Time zones are handled explicitly through VTIMEZONE definitions, which is why a well-formed event lands at the right local hour wherever it is opened.
Attendees, organisers and status fields turn a plain event into an invitation. When someone sends a meeting request, their software emits a VEVENT with ATTENDEE and ORGANIZER properties and a method such as REQUEST; your reply carries your participation status — accepted, declined or tentative — back to them.
Recurrence and subscriptions
The format’s most powerful feature is the recurrence rule, RRULE, which compresses “every second Tuesday until December” into a single line rather than hundreds of separate events. Paired with EXDATE for exceptions and RECURRENCE-ID for one-off changes to a single occurrence, it lets a repeating meeting be edited cleanly. This same machinery powers subscribable calendars, where a published .ics URL — a sports fixture list or a public-holiday feed — is polled periodically and kept up to date.
Because recurrence logic is intricate, different clients occasionally interpret edge cases slightly differently, which is the usual source of a recurring event that drifts by a day after a daylight-saving change.
Strengths
- A universal calendar standard read by Google, Outlook, Apple and most other clients.
- Compact recurrence rules express complex repeating schedules in a single line.
- Carries full invitation semantics — organisers, attendees and responses.
- Supports subscribable feeds that update automatically from a URL.
Limitations
- Recurrence and time-zone handling are intricate and interpreted unevenly across clients.
- Not designed for tabular analysis, so a busy calendar is hard to scan as a list.
- Daylight-saving and floating-time edge cases can shift events unexpectedly.
- Hand-editing is error-prone because one malformed line can break a whole event.
When to use iCalendar
Use ICS to share events, send invitations or publish a calendar that others can subscribe to across different apps. To audit or report on many events at once, exporting them to a spreadsheet is more practical.
iCalendar FAQ
- What is an ICS file?
- It is a calendar file in the iCalendar format (RFC 5545) describing events, tasks or invitations. Double-clicking one usually offers to add its events to your default calendar app.
- How do I open an ICS file?
- Google Calendar, Outlook and Apple Calendar all import .ics files directly. To examine the events as data instead, convert the file to CSV or XLSX; Morphr does this in your browser with nothing uploaded.
- How do I turn calendar events into a spreadsheet?
- Convert the ICS to CSV or XLSX so each event becomes a row with its start, end, title and location in columns. That makes it easy to sort, filter or total your events outside a calendar app.