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UTC / ISO 8601
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Timezone Converter converts times between any two timezones in the world. Select source and destination timezones, enter a time, and get the equivalent local time — with DST (daylight saving time) awareness. It also shows a side-by-side comparison of business hours across multiple timezones, and finds the best meeting times across teams in different regions.
Timezones are regions of the world that observe the same standard time. UTC (Coordinated Universal Time) is the baseline — other timezones are expressed as UTC offsets (UTC+9, UTC-5). There are currently over 600 timezone identifiers in the IANA timezone database (the standard for programming). Many timezones observe DST, shifting their offset by 1 hour seasonally. Not all countries observe DST — Japan (UTC+9), China (UTC+8), and India (UTC+5:30) have no DST.
Half-hour and quarter-hour offsets: India (UTC+5:30), Afghanistan (UTC+4:30), Iran (UTC+3:30), Nepal (UTC+5:45), Australia's Lord Howe Island (UTC+10:30 in winter, +11 in summer). UTC+5:30 is not 5 hours and 30 minutes but exactly that offset — minutes matter. These unusual offsets are historical artifacts that became standardized by local governments.
Tokyo to New York
Result: 9:00 AM JST (UTC+9) → 8:00 PM EST (UTC-5) previous day → 20:00 on July 25
Find meeting time for Tokyo/London/NYC
Result: JST 9am = UTC 0am = EST 7pm previous day → best overlap: JST 22:00 / UTC 13:00 / EST 9:00
DST-aware conversion
Result: July (EDT -4) vs January (EST -5) → same UTC time shows different local times
What is the difference between EST and EDT?
EST (Eastern Standard Time) is UTC-5, observed in winter. EDT (Eastern Daylight Time) is UTC-4, observed in summer when DST is active. The US switches to DST at 2:00 AM on the second Sunday of March (clocks spring forward to 3:00 AM) and ends DST at 2:00 AM on the first Sunday of November (clocks fall back to 1:00 AM). ET (Eastern Time) is a general term covering both EST and EDT — the actual offset depends on the time of year.
Why doesn't China have timezones despite spanning 5 geographic zones?
China officially uses a single timezone (China Standard Time, UTC+8) for the entire country, a decision made in 1949 to promote national unity. This means sunrise in Xinjiang province (geographically near UTC+6) happens around 10 AM by the clock in winter. Unofficially, people in western China often operate on 'Xinjiang time' (UTC+6) for local scheduling. India similarly uses a single timezone (UTC+5:30) despite spanning 3 geographic zones.
What is UTC offset vs IANA timezone name?
A UTC offset (UTC+5:30) describes the current difference from UTC. An IANA timezone name (Asia/Kolkata) describes the full history and DST rules for a region. A timezone name is more precise — UTC+5:30 today doesn't tell you if DST will shift the offset next month. For programming, always use IANA timezone names (from the tz database) rather than UTC offsets to correctly handle DST transitions. JavaScript's Intl API, Python's pytz/zoneinfo, and most date libraries use IANA names.
How do I schedule a meeting across timezones?
Best practices: (1) Always communicate meeting times in UTC (e.g., 'call at 14:00 UTC'). (2) Use a scheduling tool (World Time Buddy, Calendly with timezone support, Google Calendar) that shows each attendee's local time. (3) Be aware of 'date line' crossings — 09:00 Monday UTC+9 is 00:00 Sunday UTC+0 the previous day. (4) Account for DST — times that overlap in winter may not in summer if DST applies to one timezone but not another.
What is the International Date Line?
The International Date Line runs roughly along the 180° meridian in the Pacific Ocean. Crossing it westward adds a day (Monday becomes Tuesday); crossing eastward subtracts a day. The IDL is not a straight line — it bends around island nations in the Pacific to avoid splitting countries between two dates. Time zones east of it (like UTC-12) are a full day behind zones just west of it (UTC+14 in Kiribati) — the widest UTC spread on Earth is 26 hours.