Instantly convert times between any time zones around the world.
The world is divided into 24 primary time zones, each roughly 15 degrees of longitude wide, offset from Coordinated Universal Time (UTC). The continental United States spans four zones: Eastern (UTC-5), Central (UTC-6), Mountain (UTC-7), and Pacific (UTC-8). Alaska uses UTC-9 and Hawaii uses UTC-10. During daylight saving time (DST), clocks spring forward one hour in most U.S. states, shifting the offset by one hour (Eastern becomes UTC-4, for example).
Not all time zones follow whole-hour offsets from UTC. India uses UTC+5:30, Nepal uses UTC+5:45, and parts of Australia use UTC+9:30. Some regions straddle zones or use non-standard offsets for political or economic reasons. China spans five geographic time zones but uses a single official time (UTC+8) nationwide, which means sunset in western China can occur as late as 10 PM during summer.
In the United States, DST begins on the second Sunday of March and ends on the first Sunday of November. Arizona (except the Navajo Nation) and Hawaii do not observe DST. Internationally, DST schedules vary widely: the European Union changes clocks on the last Sundays of March and October, while most countries near the equator do not observe DST at all because day length varies little throughout the year.
DST creates a period in spring and fall where the offset between two locations temporarily changes. For example, London and New York are normally five hours apart, but for a few weeks in March (after the U.S. changes but before the UK does) they are four hours apart, and for a few weeks in November the gap is briefly five hours again before settling back. This makes scheduling international calls particularly error-prone during transition weeks.
When scheduling meetings with participants in multiple time zones, express the time in UTC or clearly state the time zone for each participant. "3 PM ET" is unambiguous in winter (EST, UTC-5) but during summer it could mean EDT (UTC-4). Using "3 PM ET" year-round is common practice but technically refers to different UTC offsets depending on the season. For global teams, tools that display each participant's local time reduce scheduling errors.
The International Date Line, running roughly along 180 degrees longitude through the Pacific Ocean, is where the calendar date changes. Crossing it westward skips a day; crossing eastward repeats a day. This is why flights from the U.S. to Asia often "arrive tomorrow" even with only a 10 to 12 hour flight time, and return flights may "arrive the same day" they departed.
The military uses a phonetic alphabet system for time zones. UTC is "Zulu" (Z), which is why UTC times are often written with a Z suffix (e.g., 1400Z). Eastern Standard Time is "Romeo" (UTC-5), Central is "Sierra" (UTC-6), Mountain is "Tango" (UTC-7), and Pacific is "Uniform" (UTC-8). Aviation universally uses Zulu time for flight plans, weather reports (METARs), and air traffic control to avoid ambiguity across global operations.