Timezone Converter - Convert Times Across Timezones

Before 1883: Every city set clocks by local solar noon—chaos for train schedules!
The fix: Railroads created 4 US time zones. Within a year, 85% of cities adopted them
UTC: Coordinated Universal Time replaced GMT in 1972 as the world's reference point

China spans 5 geographical zones but uses ONE timezone (Beijing Time)—sunset at 10pm in the west!
Nepal is UTC+5:45—the only country with a 45-minute offset
Australia has 3 timezones, but 5 during daylight saving (some states opt out)
Russia has 11 timezones—most of any country
France has 12 timezones (if you count overseas territories)—more than Russia!
Arizona doesn't observe DST, except the Navajo Nation, which contains the Hopi Reservation, which doesn't

Start/end dates: Vary by country—US, EU, and Australia all differ
2023 example: US changed Mar 12, EU changed Mar 26—two weeks of extra confusion
Equator countries: Don't use DST (sun rises/sets at same time year-round)
The shift: Most countries shift 1 hour, but Lord Howe Island (Australia) shifts 30 minutes
Abolishing DST: EU voted to end it in 2019—still hasn't happened

US + Europe: 2-5pm London = 9am-12pm New York = reasonable for both
US + Asia: Brutal—someone's always in the middle of the night. Try 7am Pacific = 11pm Tokyo
Europe + Asia: 8am London = 4pm Singapore = 5pm Tokyo works well
All three: Nearly impossible. Best bet: 6am Pacific = 2pm London = 10pm Tokyo (sorry, Tokyo)

ALWAYS store times in UTC in your database—convert to local only for display
Use IANA timezone names (America/New_York), not abbreviations (EST is ambiguous)
Don't assume 24 hours in a day—DST creates 23 and 25-hour days
Test your app on DST transition days (second Sunday of March, first Sunday of November in US)
JavaScript Date objects are in local time by default—a common source of bugs