ICS vs iCalendar: what’s the difference?
Short answer: ICS is the file, iCalendar is the format.
Published 1/8/2025
Terminology
ICS is the file extension you’ll see in email attachments and downloads. iCalendar is the open specification that defines how calendar data is structured inside that file. In other words: ICS is the container; iCalendar is the language.
Interoperability in practice
Because iCalendar is an open standard, it’s possible to move events between Apple Calendar, Outlook, and Google Calendar. But each app has its own interpretation of edge cases (especially recurring rules), which explains occasional differences after import.
Import vs. subscription
One‑time imports are great for static schedules. Subscriptions follow a URL, refreshing as the source changes. If you care about updates, always subscribe.
Quick instructions (optional)
To import or subscribe, see the guides linked below.