VTIMEZONE

VTIMEZONE is a time zone definition component used in the iCalendar data format to describe how local times are calculated for a given region. It encodes the rules that convert between Coordinated Universal Time (UTC) and local time, including daylight saving time transitions. VTIMEZONE helps calendar applications render correct event times across dates and locations, even when the recipient’s system time zone data differs.

A VTIMEZONE block begins with BEGIN:VTIMEZONE and ends with END:VTIMEZONE. It includes a TZID property to identify the time zone (for example, America/New_York) and one or more subcomponents of type STANDARD and/or DAYLIGHT. Each subcomponent provides properties such as DTSTART (the effective date of the rule), TZOFFSETFROM (the offset before the transition), TZOFFSETTO (the offset after the transition), and TZNAME (the time zone abbreviation). Transitions can be expressed with RRULE to define recurring changes or with RDATE to list specific dates.

Purpose and interoperability: The VTIMEZONE component allows recipients to compute local times for events reliably, regardless of the recipient’s own time zone database. It is part of the iCalendar specification (RFC 5545) and is commonly included when exporting calendar data that references explicit time zones. Some implementations reference a TZID and rely on external time zone databases, while others embed a full VTIMEZONE definition for accuracy.