Time Zone Converter
Compare a single moment across cities. Schedule meetings, coordinate with remote teams, plan international calls. DST handled automatically.
Why time zones exist
Before the railroad era, every town kept its own “solar time” based on when the sun was overhead. Train schedules forced standardization — by 1883, North American railroads adopted a four-zone system. International time zones were standardized in 1884 at the International Meridian Conference, with Greenwich as the prime meridian.
Modern time zones are mostly political, not astronomical. Borders follow countries and states, not strict 15° longitude boundaries. Some places sit one or two zones away from where the sun would suggest (China, Spain, parts of Russia) for political or economic reasons.
Daylight saving time (DST)
~70 countries observe DST, shifting clocks forward by 1 hour in spring and back in fall to better align daylight with waking hours. US: second Sunday of March (spring forward) and first Sunday of November (fall back). EU: last Sundays of March and October.
Notable exceptions:
- Most of Arizona, Hawaii, and US territories — no DST.
- Russia, Turkey, Iceland, most of Asia and Africa — no DST.
- Brazil — discontinued DST in 2019.
- Southern hemisphere DST is reversed (spring forward in October).
The calculator uses the IANA time zone database, which tracks DST rules and historical changes for every region, including obscure cases (e.g., Indiana counties that used to differ).
Common meeting-planning patterns
- US East Coast ↔ Europe: 5–9 hours difference. 9am ET = 2pm UK = 3pm Paris/Berlin. Mornings ET / afternoons EU is a common overlap.
- US West Coast ↔ Asia: 15–17 hours difference. 8am PT = 11pm Tokyo / 12am Sydney. Tough overlap; usually one team works late or early.
- India ↔ US: 9.5–13.5 hour difference (across IST). Indian morning = US night, Indian evening = US morning.
- Same-continent: Easy. ET ↔ PT = 3 hours; useful overlap 9am–6pm in both.
UTC offsets and acronyms
Common abbreviations:
- UTC — Coordinated Universal Time (the modern reference).
- GMT — Greenwich Mean Time. For practical use, equal to UTC.
- EST / EDT — US Eastern Standard / Daylight Time (UTC−5 / −4).
- CST / CDT — US Central Standard / Daylight Time (UTC−6 / −5). Also “China Standard Time” (UTC+8) — the same acronym!
- PT / PDT / PST — Pacific Time (UTC−8 / −7).
- BST — British Summer Time (UTC+1).
- CET / CEST — Central European Time / Summer Time (UTC+1 / +2).
- JST — Japan Standard Time (UTC+9, no DST).
- IST — Indian Standard Time (UTC+5:30) or Israel Standard Time (UTC+2). Acronym collision.
For unambiguous communication, prefer city names (“3pm in Tokyo”) or UTC offsets (“3pm UTC+9”) over acronyms. Acronyms collide; cities don't.
Edge cases that trip people up
- Crossing the International Date Line — you can lose or gain a calendar day. Tokyo 9am Friday = LA 5pm Thursday.
- Half-hour and quarter-hour zones — Mumbai is UTC+5:30, Nepal UTC+5:45. Off-by-30-min meeting errors are surprisingly common.
- DST transitions — “spring forward” means there's no 2:30am-3:00am the night DST starts. “Fall back” means 1:30am-2:00am happens twice. Avoid scheduling meetings during these windows.
- Antarctica — researchers usually keep the time zone of their supply nation. Multiple zones can apply at the same physical location.