Sources of Time Zone Information

Sources of time zone data for calendar implementations.

IANA Time Zone Database

The primary source. Available at iana.org/time-zones. Contains:

• Current and historical time zone rules for all worldwide locations.
• Daylight saving time transition dates.
• UTC offsets and their changes over time.
• Leap seconds information.

Updated approximately 6–8 times per year as governments announce changes.

Time Zone Data in Operating Systems

• Linux/macOS — tzdata package, usually at /usr/share/zoneinfo/.
• Windows — Windows Time Zone database. Maps to IANA IDs via Unicode CLDR.
• Java — Java Time API uses IANA data bundled with the JRE.

ICU (International Components for Unicode)

Provides time zone data with Unicode CLDR mappings. Available for C/C++, Java, and JavaScript.

Distributions

• tzdata — Raw IANA data, processed into binary format by zic (zone info compiler).
• moment-timezone — JavaScript library with IANA data.
• pytz / zoneinfo — Python libraries.
• Luxon — JavaScript date library with built-in time zone support.