UTCTimezone Converter
Convert time between different timezones
Timezone Converter Complete Guide
Instantly convert times across major world timezones — Seoul (KST), UTC, New York (EST/EDT), Los Angeles (PST/PDT), London (GMT/BST), Berlin (CET/CEST), Tokyo (JST), Shanghai (CST), and Sydney (AEST). Essential for scheduling global team meetings, planning international deployment windows, and confirming times for worldwide events.
Understanding Timezone Systems — UTC / GMT / DST
- UTC (Coordinated Universal Time): The international standard based on atomic clocks. All timezones are expressed as UTC ± offset. Servers and databases should always store time in UTC.
- GMT (Greenwich Mean Time): The historical standard based on solar time at Greenwich, UK. Numerically near-identical to UTC but technically distinct. Modern systems use UTC.
- DST (Daylight Saving Time): Clocks advance 1 hour in summer in the US, Europe, and others. Korea (KST), Japan (JST), and China (CST) do not observe DST.
IANA Timezone Database
Operating systems and programming languages use the IANA timezone database (tz database / zoneinfo). Using IANA IDs like Asia/Seoul or America/New_York instead of raw offsets (+09:00) handles DST transitions automatically.
| City | IANA ID | Standard | Summer (DST) |
|---|---|---|---|
| Seoul | Asia/Seoul | KST (UTC+9) | None |
| New York | America/New_York | EST (UTC-5) | EDT (UTC-4) |
| LA | America/Los_Angeles | PST (UTC-8) | PDT (UTC-7) |
| London | Europe/London | GMT (UTC+0) | BST (UTC+1) |
| Berlin | Europe/Berlin | CET (UTC+1) | CEST (UTC+2) |
Commonly Confused: KST / PST / EST
- KST vs JST: Both are UTC+9 — Seoul and Tokyo are always on the same time.
- PST vs PDT: PST is winter (UTC-8), PDT is summer (UTC-7). Seoul to LA gap: 17h in winter, 16h in summer.
- EST vs EDT: EST is winter (UTC-5), EDT is summer (UTC-4). Seoul to New York: 14h in winter, 13h in summer.
- CST caution: Shanghai CST (China Standard Time, UTC+8) vs US CST (Central Standard Time, UTC-6) — completely different offsets.
Preventing Timezone Bugs in Development
- Store in UTC: Always store UTC in servers and databases; convert to local time only for display.
- Use IANA IDs:
America/New_Yorkinstead of raw offsets for automatic DST handling. - JavaScript:
new Date()is UTC-based; usetoLocaleString()for localization.Date.now()returns millisecond Unix timestamp. - API design: Use ISO 8601 (
2024-01-01T00:00:00Z) with explicit timezone info in transit.
FAQ
Practically yes, technically no. UTC is the international standard based on atomic clocks; GMT is the historical solar time at Greenwich. Use UTC in modern development.
No. Korea Standard Time (KST) is fixed at UTC+9 with no DST adjustments — same offset as Japan (JST) year-round.
The US Pacific region observes PDT (UTC-7) from the second Sunday of March through the first Sunday of November, and PST (UTC-8) otherwise. This tool calculates automatically based on the selected date.
In development and infrastructure, yes — UTC is the standard. For end users, convert to their local timezone for display.