Standards

IANA Time Zone Database

iana tzdb

Overview

The IANA Time Zone Database, commonly known as the tz database or Olson database, is maintained by the Internet Assigned Numbers Authority (IANA). It provides a comprehensive record of UTC offsets, daylight saving transition dates, and historical rule changes for every time zone in the world.

Naming Convention

Time zones are identified using a "Region/City" format, such as Asia/Tokyo, America/New_York, and Europe/London. City names are used rather than country names because many countries span multiple time zones (e.g., the United States, Russia, and Australia). Approximately 600 zone identifiers are defined in the database when aliases (Link entries) are counted, and about 340 of them are canonical zones.

Updates and Usage

The tz database is updated a few times per year (2 to 4 times in recent years), with new releases issued whenever a country announces changes to its daylight saving rules or abolishes them entirely. Linux, macOS, Java, Python, and JavaScript (via the Intl API) all rely on this database for time conversions. Windows keeps its own set of time zone IDs, such as "Tokyo Standard Time", and maps them to IANA names through the CLDR mapping table. Keeping systems up to date is essential for accurate results - running an outdated version can produce incorrect conversions for affected regions.

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Related Terms

Basics

Time Zone

timezone

A region of the globe that observes a uniform standard time for legal, commercial, and social purposes.

Basics

Daylight Saving Time

dst

The practice of advancing clocks by one hour during warmer months to extend evening daylight.

Standards

UTC (Coordinated Universal Time)

utc

The primary time standard by which the world regulates clocks and time, serving as the basis for civil timekeeping globally.

Technology

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2026-05-15

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Choosing between DATE, TIME, TIMESTAMP, and TIMESTAMPTZ shapes whether your application handles time zones correctly. This article walks through reservation systems, future event scheduling, audit trails, and migration strategy for legacy schemas that ignored time zones.

2026-05-15

Basics