hCalendar (short for HTML iCalendar) is a microformat standard for displaying a semantic (X)HTML representation of iCalendar-format calendar information about an event, on web pages, using HTML classes and rel attributes.

It allows parsing tools (for example other websites, or browser add-ons like Firefox's Operator extension) to extract the details of the event, and display them using some other website, index or search them, or to load them into a calendar or diary program, for instance. Multiple instances can be displayed as timelines.

Consider this semi-fictional example:

The HTML mark-up might be:

hCalendar mark-up may be added using span HTML elements and the classes vevent, summary, dtstart (start date), dtend (end date), location and url:

Note the use of the abbr element to contain the machine readable, ISO8601, date-time format for the start and end times.

Concerns have been expressed that, where it occurs, the use of the abbr element (using the so-called abbr-design-pattern) in the above manner causes accessibility problems, not least for users of screen readers and aural browsers. The newer h-event microformat therefore uses the HTML5 element time instead:

The Geo microformat is a part of the hCalendar specification, and is often used to include the coordinates of the event's location within an hCalendar.