TZOFFSETFROM0200

TZOFFSETFROM is a property used in the iCalendar specification (RFC 5545) to describe how the UTC offset changes during a time zone transition. It appears within a VTIMEZONE component, inside STANDARD or DAYLIGHT subcomponents, which model the historical and future daylight saving rules of a region. The TZOFFSETFROM property specifies the UTC offset in effect immediately before a clock change, such as when moving into or out of daylight saving time. The value is a signed offset in the form ±HHMM, indicating the amount that must be added to UTC to obtain local time before the transition. For example, TZOFFSETFROM:+0100 indicates UTC+01:00 before the change, commonly paired with TZOFFSETTO:+0200 for the spring transition to daylight saving time.

In practice, TZOFFSETFROM is always paired with TZOFFSETTO; the pair defines the exact transition. A transition might start at a specific date and time (DTSTART) or follow a recurrence rule (RRULE). This pairing allows calendar applications to compute local times across DST boundaries and to translate between local time and UTC accurately.

Canonical notation requires a leading sign on the offset value. The string TZOFFSETFROM0200, lacking a sign, would ordinarily be represented as TZOFFSETFROM:+0200 or TZOFFSETFROM:-0200 in ICS data. Some human-readable documents may omit the sign, but robust ICS parsers expect the signed form. Understanding TZOFFSETFROM in conjunction with TZOFFSETTO is essential for correct time zone definitions in calendar data.