Convert times between any two timezones with DST-aware calculations. Powered by the IANA timezone database via JavaScript's Intl API.
New York (EST) (UTC-4)
Sat, Mar 28, 2026, 05:13:00 AM
Seoul (KST) (UTC+9)
Sat, Mar 28, 2026, 06:13:00 PM
Earth has 24 primary time zones, but the actual count is closer to 38 due to half-hour and 45-minute offsets. India uses UTC+5:30, Nepal uses UTC+5:45, and the Chatham Islands use UTC+12:45. The IANA timezone database (tzdata) tracks over 590 timezone identifiers, accounting for historical changes, political boundaries, and DST rules dating back to the 1800s. At any given moment, there are 3 different calendar dates simultaneously present on Earth.
About 70 countries observe DST, but they switch on different dates. The US springs forward on the second Sunday of March; the EU on the last Sunday of March. Southern hemisphere countries reverse the pattern. This means the UTC offset between New York and London is -5 hours for most of the year, but -4 hours for ~3 weeks in March and ~1 week in November when only one has switched. For scheduling across timezones, always store times in UTC and convert at display time.
Timezone abbreviations like “CST” are ambiguous: it could mean Central Standard Time (UTC-6), China Standard Time (UTC+8), or Cuba Standard Time (UTC-5). The IANA timezone database uses unambiguous identifiers like America/Chicago, Asia/Shanghai, and America/Havana. Always use IANA names in code and APIs. This tool uses IANA identifiers internally and JavaScript's Intl API for accurate DST-aware conversions.
The date line roughly follows the 180th meridian but zigzags to keep island nations on the same date as their trading partners. Samoa switched from UTC-11 to UTC+13 in 2011, skipping December 30 entirely, to align with Australia and New Zealand. Kiribati spans UTC+12 to UTC+14 — the first place on Earth to see each new day. When converting across the date line, always verify whether the date changes; a meeting at 2 PM Monday in Tokyo is 10 PM Sunday in New York.
Yes. This tool uses JavaScript's Intl.DateTimeFormat with IANA timezone identifiers, which automatically applies DST rules based on the selected date. The offset shown reflects the actual UTC offset for that specific date and timezone, including any DST adjustment.
Half-hour offsets exist because timezone boundaries follow political, not geographic, lines. India adopted UTC+5:30 as a compromise between Kolkata (which would naturally be +6) and Mumbai (+5). Iran uses UTC+3:30, and Myanmar uses UTC+6:30. Nepal's UTC+5:45 offset was chosen to be exactly 15 minutes ahead of India as a symbol of national identity.
Always communicate meeting times with an explicit timezone or UTC offset. “3 PM EST” is unambiguous, but “3 PM” is not. For recurring meetings, be aware that DST transitions can shift the meeting time by an hour for some participants. Consider sending calendar invites with the time in UTC, as calendar apps will automatically convert to each participant's local time.