Time Zone Calculator

A time zone is a region of the globe that observes a uniform standard time. Time zones are offset from Coordinated Universal Time (UTC) and usually differ by whole hours — though some zones (India, Iran, Nepal, and others) use 30- or 45-minute offsets.

The contiguous US has four main zones: Eastern (ET, UTC−5/−4), Central (CT, UTC−6/−5), Mountain (MT, UTC−7/−6), and Pacific (PT, UTC−8/−7). Alaska (AKT, UTC−9/−8) and Hawaii (HT, UTC−10, no DST) have their own zones. The offsets shift by +1 hour during Daylight Saving Time.

DST is the practice of moving clocks forward one hour in spring ('spring forward') and back one hour in fall ('fall back'). Most US states observe DST. Arizona (except the Navajo Nation) and Hawaii do not. This calculator uses your browser's Intl API, which handles DST transitions automatically and correctly.

Pacific Time is always 3 hours behind Eastern Time — whether both are on standard time or both on daylight saving time. So 9:00 AM ET = 6:00 AM PT. The tricky case is the brief window each spring and fall when one region has switched but the other hasn't — this calculator handles that automatically.

UTC (Coordinated Universal Time) is the global time standard. All time zones are expressed as UTC+ or UTC− offsets. UTC is essentially the same as GMT (Greenwich Mean Time) for everyday purposes. Servers, APIs, and aviation all use UTC to avoid ambiguity.

Calendar apps store meeting times in UTC and display them in your local time zone. If a meeting was scheduled before a DST transition, the UTC time is unchanged — but the local display shifts by one hour. Always verify meeting times around DST change weekends (second Sunday in March and first Sunday in November in the US).