UTC (Coordinated Universal Time) is the global standard time that every time zone is defined from. It's kept by a network of atomic clocks around the world and never changes for daylight saving time. New York is UTC−5 in winter and UTC−4 in summer; Los Angeles is UTC−8 and UTC−7; India is UTC+5:30 all year. When people say "Zulu time" in aviation or the military, they mean UTC.
US time zones vs UTC
| Zone | Standard time | Daylight time | Noon UTC is… |
|---|---|---|---|
| Eastern | UTC−5 (EST) | UTC−4 (EDT) | 7 AM EST / 8 AM EDT |
| Central | UTC−6 (CST) | UTC−5 (CDT) | 6 AM CST / 7 AM CDT |
| Mountain | UTC−7 (MST) | UTC−6 (MDT) | 5 AM MST / 6 AM MDT |
| Pacific | UTC−8 (PST) | UTC−7 (PDT) | 4 AM PST / 5 AM PDT |
| Alaska | UTC−9 (AKST) | UTC−8 (AKDT) | 3 AM AKST / 4 AM AKDT |
| Hawaii | UTC−10 (HST) | No DST | 2 AM HST |
To convert UTC to your local time, add your offset: 18:00 UTC + (−4) = 14:00, or 2:00 PM EDT. To go from local time to UTC, subtract it. The converter does this for you: UTC to EST and EST to UTC. For when Eastern time switches, see EST vs EDT.
UTC vs GMT
For everyday purposes, UTC and GMT show the same time, but they're different things:
- GMT (Greenwich Mean Time) is a time zone, based historically on the Sun's position at the Royal Observatory in Greenwich, London. The UK uses GMT in winter and switches to BST (GMT+1) in summer.
- UTC is a time standard based on atomic clocks. It's the reference that GMT and every other zone are now defined from, and it never changes with the seasons.
So in July, London is on UTC+1, not UTC. Saying "GMT" when you mean the world reference is common, but "UTC" is the precise term.
Why is it "UTC" and not "CUT"?
English speakers proposed CUT (Coordinated Universal Time), and French speakers proposed TUC (Temps Universel Coordonné). The International Telecommunication Union chose UTC as a neutral compromise that favors neither language, matching other Universal Time variants such as UT0, UT1 and UT2.
How UTC is kept
UTC is calculated by the International Bureau of Weights and Measures (BIPM) near Paris, from more than 400 atomic clocks in about 80 laboratories worldwide. In the US, the National Institute of Standards and Technology (NIST) and the US Naval Observatory maintain their own versions, which stay within billionths of a second of UTC. Your phone and computer get their time from these sources through networks and GPS.
Leap seconds
Atomic clocks are steadier than the Earth, whose rotation varies slightly. To keep UTC within 0.9 seconds of the Earth's rotation, a leap second has occasionally been added, usually as 23:59:60 UTC on June 30 or December 31. Since 1972, 27 leap seconds have been added; the most recent was on December 31, 2016.
Leap seconds cause problems for computer systems, so in 2022 the General Conference on Weights and Measures voted to stop adding them by 2035, letting UTC and the Earth's rotation drift apart by a larger amount before any correction.
Where you'll see UTC
- Aviation: flight plans and air traffic control use UTC ("Zulu"), written like 1430Z. See military time explained.
- Computing: servers, databases and logs usually store timestamps in UTC, and many use ISO 8601 format: 2026-10-03T14:30:00Z.
- Weather and science: forecasts, satellite data and space missions are timed in UTC.
- Online events: global product launches, game releases and webinars often announce times in UTC.
- Ham radio and shipping: logs and schedules use UTC to avoid confusion across zones.
Common UTC offsets around the world
| Place | Offset (standard) |
|---|---|
| London | UTC+0 (UTC+1 in summer) |
| Paris, Berlin | UTC+1 (UTC+2 in summer) |
| Dubai | UTC+4 |
| Karachi | UTC+5 |
| India | UTC+5:30 |
| China, Singapore | UTC+8 |
| Tokyo | UTC+9 |
| Sydney | UTC+10 (UTC+11 in its summer) |
Offsets range from UTC−12 to UTC+14, and a few zones use 30- or 45-minute offsets. Learn more in time zones explained.
Scheduling internationally? State your time in UTC plus one local zone, like "15:00 UTC (11:00 AM EDT)", and check it with the time zone converter.
Frequently asked questions
Is UTC the same as GMT?
They show the same time, but UTC is the atomic time standard and GMT is the UK's winter time zone.
Does UTC change for daylight saving time?
No. UTC is the same all year; local time zones shift around it.
How many hours ahead is UTC from New York?
UTC is 5 hours ahead of New York in winter (EST) and 4 hours ahead in summer (EDT).