Gera Tools

IANA Time Zone Identifiers

Search IANA tz database identifiers by name, country or UTC offset.

Searchable IANA tz database reference: canonical Area/Location identifiers such as Europe/London and Asia/Yerevan, their standard-time UTC offset, whether they observe DST, and the country they belong to.

Why use IANA identifiers instead of fixed UTC offsets?

An identifier like Europe/London encodes the full history and future rules of a region, including daylight saving transitions. A fixed offset like +00:00 cannot follow these rules, so dates computed across a DST boundary would be wrong.

IANA time zone identifier reference

The IANA tz database (also called the Olson or zoneinfo database) is the authoritative source for time zone rules used by operating systems and most programming languages. Each zone has a canonical identifier in Area/Location form, like Europe/London or Asia/Yerevan, that captures the region’s full history of offsets and daylight saving transitions. This reference lets you search those identifiers by city, country or offset.

How it works

An identifier names a region whose local time has followed the same rules since 1970. To find the wall-clock time you take UTC, apply the zone’s current offset, and add an hour during daylight saving if the zone observes it:

local = UTC + base_offset (+1h while DST is in effect)

The database tracks every transition, so a library given America/New_York knows it was UTC-5 in winter and UTC-4 in summer, and exactly when each switch happened. The standard-time offset shown here is the base (winter) value; zones flagged as observing DST move forward in their local summer.

Identifiers use a stable representative city, not a political name, because cities rarely rename while timezone politics change often. Some zones use non-whole-hour offsets — India is +05:30, Nepal +05:45 — which is why you must rely on identifiers rather than assuming whole-hour offsets.

Tips and notes

  • Always store and schedule using an identifier (Asia/Tokyo), never a raw offset, so DST and historical changes are handled for you.
  • UTC is the right choice for timestamps and logs; convert to a user’s zone only at display time.
  • Northern and Southern Hemisphere DST run in opposite halves of the year — Australia/Sydney springs forward when Europe/Berlin falls back.
  • Treat Etc/GMT±N as legacy: the sign is inverted (Etc/GMT-5 is UTC+5) and they never observe DST.