What Is the IANA Time Zone Database

The IANA time zone database (tz database or Olson database) is the authoritative rule set used by operating systems, browsers, and servers worldwide. Each zone has a unique ID such as Asia/Shanghai, America/New_York, or Europe/London. Global Clock and most calendar apps rely on it to compute local time and daylight saving transitions.

Why "UTC+8" is not enough

A numeric offset only describes the difference from UTC at one moment. It cannot express rule changes over time. Turkey has toggled DST policies; Samoa skipped a calendar day when moving across the date line in 2011. IANA stores these histories so software can resolve Asia/Istanbul or Pacific/Apia correctly for any date.

Naming basics

• Format: Continent/City — e.g. Europe/Paris, Africa/Cairo
• The city is representative, not always the national capital
• US zones use America/; Australia uses Australia/; all of China uses Asia/Shanghai
• Etc/GMT forms exist but geographic names are preferred in apps

Practical use

For meetings, code, or travel, prefer IANA IDs over abbreviations like EST or CST, which are ambiguous. Each country page in Countries lists the capital's IANA zone. Use the Convert with a specific date for automatic DST handling. See also UTC Basics and DST Guide.