Time Zone List
A time zone supplies rules for interpreting a date in a region. It is different from a UTC offset at one instant. Use an IANA ID such as Asia/Tokyo to identify the region.
How to Read Time Zones
An offset may change with daylight saving or rule changes. A conversion needs both a zone and a date.
Key terms
- IANA IDs include Asia/Tokyo and America/New_York. Region/city is a common shape, but Etc/UTC and deeper names also exist. Not every city has a separate ID.
- A UTC offset describes the difference at one instant. +09:00 alone does not say whether the region is Tokyo or somewhere else.
- Abbreviations such as CST have several meanings. Do not rely on abbreviations alone when regional rules matter.
- DST is a seasonal clock change. One-hour shifts are common, but the amount and transition dates differ among regions.
Representative Time Zones
Offsets below are for 12:00 UTC on January 15 and July 15, 2026. Comparing two dates avoids treating a standard offset as permanent. For other dates, use that date and updated time-zone data.
Offsets by region
| IANA ID | Jan 15 | Jul 15 |
|---|---|---|
| Asia/Tokyo | +09:00 | +09:00 |
| Asia/Seoul | +09:00 | +09:00 |
| Asia/Shanghai | +08:00 | +08:00 |
| Asia/Taipei | +08:00 | +08:00 |
| Asia/Singapore | +08:00 | +08:00 |
| Australia/Sydney | +11:00 | +10:00 |
| Europe/London | +00:00 | +01:00 |
| Europe/Berlin | +01:00 | +02:00 |
| Europe/Paris | +01:00 | +02:00 |
| America/New_York | -05:00 | -04:00 |
| America/Chicago | -06:00 | -05:00 |
| America/Denver | -07:00 | -06:00 |
| America/Los_Angeles | -08:00 | -07:00 |
| America/Phoenix | -07:00 | -07:00 |
| America/Sao_Paulo | -03:00 | -03:00 |
| Etc/UTC | +00:00 | +00:00 |
Interpreting the differences
- Tokyo and Seoul are +09:00 on both dates. The table does not imply that their offsets have always been the same historically.
- Sydney is in the Southern Hemisphere: +11:00 in January and +10:00 in July. Do not apply Australia/Sydney to all of Australia.
- America/Phoenix is -07:00 on both dates, but not all of Arizona follows the same rules; the Navajo Nation and other locations need appropriate treatment.
- Japan is 14 hours ahead of New York on the January date and 13 hours ahead on the July date. The local calendar date can differ too.
- São Paulo is -03:00 on both dates but observed DST in the past. Do not convert historical records using only a present-day offset.
Operational Tips
Distinguish twenty-four hours later from the same local time tomorrow, and keep time-zone rules updated.
Checklist
- Epoch time can store an instant. A recurring 9 a.m. appointment also needs local time, an IANA ID, and recurrence rules.
- Across DST, adding exactly 86,400 seconds in UTC may not yield the intended local time tomorrow.
- Display the UTC offset. Retain an IANA ID separately if the region matters.
- Check supported IDs and the time-zone database version. The OS and application may use separate copies.
- See storage, schedules, and DST examples and Unix time conversions for the complete workflow.
Specification and data
IANA Time Zone Database / Theory and pragmatics / Asia / Australasia / Europe / North America / South America