timezones Browse time zones

timezones.now guides & articles

10 in-depth guides on Time Zones and related topics.

Time zones explained

Time zones explained Daylight Saving Time Around the World: Who Changes Their Clocks, and When Which countries still move their clocks, how the northern and southern seasons differ, which nations have abandoned the practice, and why no two regions change on the same date. 5 min read Time zones explained Half-Hour Time Zones and Quarter-Hour Offsets: Why Some Clocks Sit Off the Hour India, Nepal, Newfoundland and the Chatham Islands keep clocks that are thirty or forty-five minutes off the hour. Where those offsets came from, and the bugs they still reveal. 5 min read Time zones explained Historical Time Zone Changes: How Countries Move Their Clocks Countries move their clocks by decree, sometimes with days of notice. A record of the notable shifts, and why converting an old timestamp needs the rules that applied at the time. 5 min read Time zones explained How Many Time Zones Are There? Why 24 Is the Wrong Answer The world does not have 24 time zones. Counting by UTC offset gives close to forty, counting by IANA identifier gives several hundred, and both answers are correct. 5 min read Time zones explained The IANA Time Zone Database: What It Is and Why Software Needs It A plain explanation of the IANA time zone database: what it records, who maintains it, how its Area/Location zone names are built, and why software cannot manage without it. 5 min read Time zones explained UTC vs GMT: The Difference Between Atomic Time and Solar Time One is an atomic time standard kept in step with the Earth by leap seconds, the other is mean solar time at Greenwich. When each term is correct, and why they are not interchangeable. 5 min read Time zones explained Why the China Time Zone Covers Five Zones' Worth of Longitude China spans about sixty degrees of longitude and keeps a single clock. How the 1949 unification came about, how Xinjiang works around it, and what it does to sunrise. 5 min read

Reference tables

Reference tables Time Zone Abbreviations Are Ambiguous: Why IST, CST and BST Mean Several Things IST, CST, BST and AST each stand for several different zones with different offsets. A reference to the worst clashes, why no standards body governs them, and what to record instead. 5 min read Reference tables Time Zones for Developers: What to Store, What to Trust, What to Test A working reference on time zones for developers: what to persist, why offsets and abbreviations are not identifiers, how to survive daylight saving transitions, and how to keep zone data fresh. 5 min read Reference tables UTC Offsets Explained: The Full Range From UTC−12 to UTC+14 A reference guide to UTC offsets: the full range from UTC−12 to UTC+14, why it spans more than a day, the places at each extreme, and why an offset is not a time zone. 5 min read