What is an ICS file?

What ICS is

ICS is a plain-text format you can open in any editor. It is used for moving data between programs.

The extension is .ics, and the full name is iCalendar. Both matter less than what the file can hold, which is what the rest of this page is about.

Where ICS came from

It dates from 1998. The specification is RFC 5545.

A format that has been readable for that long is a format worth trusting with something you want back in ten years.

The specification is public

Anyone can implement it without asking permission or paying a licence, which is why it turns up in so many programs and why files written twenty years ago still open.

Nothing is thrown away

ICS stores its content exactly. Saving it again changes nothing, so it can be opened, edited and re-saved as often as you like without accumulating damage — which is what makes it a working format rather than a delivery one.

What opens ICS

Google Calendar, Apple Calendar and Microsoft Outlook read it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

Opening it in a browser

No browser reads it.

That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.

It is a working format

ICS is meant to be opened and changed. Keep the file in this format for as long as the work is going on, and export from it whenever a finished copy is needed.

The facts, in one place

Converting ICS to something else

• ICS to CSV

Formats worth considering instead of ICS

• Comma-Separated Values