TZOFFSETTO

TZOFFSETTO is a property used in the iCalendar specification (RFC 5545) within the VTIMEZONE component. It specifies the time difference, relative to Coordinated Universal Time (UTC), that applies after a time zone transition. In practice, TZOFFSETTO appears together with TZOFFSETFROM in STANDARD and DAYLIGHT subcomponents to describe transitions such as entering or leaving daylight saving time.

The value of TZOFFSETTO is a signed numeric offset from UTC, written without a colon, in the form +HHMM or -HHMM (for example, +0200 or -0500). This offset indicates the new standard or daylight saving offset that should be used after the transition. TZOFFSETFROM provides the previous offset, allowing calendar clients to understand the change.

Typical usage is seen in VTIMEZONE definitions that model a region’s DST rules. For each transition, a pair of lines is provided: TZOFFSETFROM shows the old offset, and TZOFFSETTO shows the new offset. Together with DTSTART (the transition moment) and TZNAME (the label for the offset, such as CET or CEST), TZOFFSETTO helps software calculate local times across DST changes.

Example snippet:

BEGIN:VTIMEZONE

TZID:Europe/Berlin

BEGIN:STANDARD

DTSTART:19961027T030000

TZOFFSETFROM:+0200

TZOFFSETTO:+0100

TZNAME:CET

END:STANDARD

BEGIN:DAYLIGHT

DTSTART:19960331T010000

TZOFFSETFROM:+0100

TZOFFSETTO:+0200

TZNAME:CEST

END:DAYLIGHT

END:VTIMEZONE

TZOFFSETTO is primarily relevant for calendar data exchange and time zone representations in ICS files, not for general system timekeeping.