Software, thoughtfully built.

Last updated August 1 2025

Did you know that Swift's TimeZone.knownTimeZoneIdentifiers returns 438 values? That's 18 times the "24-time-zones-around-the-globe" posters we grew up with. Here's why, and what every engineer (or trivia lover) should know about the wonderfully messy world of civil time.

Time Zones Are Weird: A Developer-Friendly Tour

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1. How Many Time Zones Are There, Really?

Category	Count	Examples
Whole-hour offsets	27	New York (UTC-5), Tokyo (UTC+9)
Half-hour offsets	9	India (UTC+5:30), Newfoundland (UTC-3:30)
Quarter-hour offsets	3	Nepal (UTC+5:45), Chatham Islands (UTC+12:45)
Daylight-Saving variants*	284 (ish)	U.S., Europe, parts of Australia

*If you treat each DST switch as a "new" zone, the number balloons. The IANA database, which macOS / iOS rely on, currently tracks ~438 distinct identifiers to cover historical and political quirks.

2. Fractional & Exotic Offsets

Nepal (UTC+5:45) : the only 45-minute offset that covers an entire country.
Eucla, Australia (UTC+8:45) : a town of ~50 people decided 45 minutes suited them better.
Lord Howe Island (UTC+10:30 → +11:00 in summer) : a half-hour DST shift!
Iran (UTC+3:30) and Afghanistan (UTC+4:30) : yes, neighbors on the half-hour.

For a full list of fractional zones, TimeandDate.com maintains a handy table.

3. Daylight Saving Chaos

~70 countries still change clocks twice a year, but the list shrinks almost annually (Mexico dropped most of its DST in 2023; Egypt re-added it in 2024).
The European Union voted in 2019 to let members quit DST, but political gridlock means nothing has happened yet.
In the U.S., Hawaii, most of Arizona, and Puerto Rico stay on standard time year-round.
Southern-hemisphere nations (e.g., Australia, New Zealand, Chile) "spring forward" in September or October: the opposite of the north.

For a current map, see TimeandDate's DST atlas.

4. Case Studies in Weirdness

Indiana, USA

Until 2006, some counties observed DST, others didn't; some were on Eastern Time, others on Central. TV guides were a nightmare. Today the state is mostly Eastern, but a dozen counties near Chicago & Evansville still run on Central.

Antarctica

With no "sunrise" cues, research stations pick whatever time suits flight logistics. The U.S. Amundsen-Scott South Pole Station follows New Zealand time (UTC+12 / +13) because that's where supply planes originate.

China

Spans five geographical zones but uses a single civil time: Beijing Time (UTC+8). In Xinjiang, many locals run an unofficial UTC+6 "Xinjiang Time" for daily life, so a 9 AM appointment might be 11 AM Beijing Time.

Kiribati & the International Date Line

In 1995 Kiribati shifted its eastern islands from UTC-10 to UTC+14, dragging the date line eastward so the whole country shares one calendar day. Result: Kiribati is first to ring in the New Year each January 1. Read the backstory.

5. Software Gotchas (and How to Dodge Them)

Issue	Why it bites	What to do
Ambiguous times	2025-11-02 01:30 happens twice in New York when clocks fall back.	Store timestamps in UTC; use local time only for display.
"Non-existent" times	2025-03-09 02:30 never exists in L.A.: clocks jump to 03:00.	Let date-parsing APIs throw errors; never build your own parser.
Political changes	Russia killed DST in 2014; Turkey adopted permanent DST in 2016.	Ship the latest IANA tzdata with each app update.
Hard-coded abbreviations	"EST" is ambiguous (Eastern Standard vs. Australian Eastern Standard).	Prefer numeric offsets (`UTC−05:00`), or use localized long names from the OS.
Assuming 24 zones	Scheduling across India (+5:30) or Nepal (+5:45) breaks.	Treat offsets as arbitrary `HH:mm` in your database schema.

Apple's guide NSDate and Calendars is an excellent deep dive.

6. Alternative Proposals

"All-UTC" business : Some global teams schedule meetings strictly in UTC to avoid DST math.
Swatch Internet Time (.beat) : Divides the day into 1000 ".beats." Fun trivia, little adoption.
Decimal time : Tried during the French Revolution; failed because old habits die hard.
Permanent Standard Time / Permanent DST : Actively debated in the U.S. and EU.

7. Fun Facts to Drop at Parties

UTC+14 and UTC−12 are only 30 NM (55 km) apart south of Kiribati, yet they're a full day apart in the calendar.
New Year's Eve lasts 26 hours on Earth, from Kiritimati (UTC+14) to Baker Island (UTC−12).
Chatham Islands' time signal includes the world's only broadcast on a quarter-hour offset.
There's a UTC+13:45 proposal for Tokelau, but locals couldn't agree on the extra 15 minutes.
The U.S. Department of Defense assigns a single-letter code to each whole-hour zone -"Zulu" (Z) is UTC, "Foxtrot" (F) is UTC+6, etc. (Yes, they ignore half-hours.)
Unix time skipped 10 seconds in 1972 when leap seconds were introduced.

Key Takeaways

Time == politics. Offsets change when parliaments change their minds.
Use proven libraries: the IANA time-zone database or platform APIs.
Store UTC, display local. Anything else invites bugs.
Always allow for non-integer offsets and DST transitions in scheduling code.

The world runs on a patchwork of conventions stitched together by history, geography, and the occasional airline route. Embrace the chaos, and let your software (and next trivia night) handle it with grace.

Have another favorite time-zone oddity? Drop it in the comments; just don't call it Greenwich Mean Time in July 😉