What Is UTC? UTC vs GMT Explained
UTC is the time standard the whole world sets its clocks from. GMT is the older one, based on the sun over Greenwich in London. Day to day they show the same time, but computers, airlines and scientists all work in UTC.
Why the letters are in the "wrong" order
UTC stands for Coordinated Universal Time, and yes, the letters look jumbled on purpose. English speakers wanted CUT, French speakers wanted TUC, and the international bodies settled on UTC because it didn't favour either side.
So how do UTC and GMT differ?
GMT began as the average solar time at the Royal Observatory in Greenwich, so it follows the Earth's rotation, and the Earth doesn't spin at a perfectly steady speed. UTC is built from atomic clocks around the world, which makes it steadier. The two never drift more than a second apart, so for a meeting or a timestamp you can treat them as the same thing.
One thing people regularly mix up is London itself. The UK is only on GMT in winter; in summer it switches to British Summer Time, which is UTC+01:00.
Is UTC a time zone?
People use it as one, but it's really the yardstick every zone is measured against. India is UTC+05:30, and New York is UTC-05:00 in winter and UTC-04:00 in summer, while UTC itself never shifts for daylight saving. You can see the live reading on our UTC time now page.
Why computers and pilots insist on it
If every system stamped times in its own local zone, mistakes would pile up fast. A flight that crosses six zones, or a server log shared by teams in five countries, needs one clock that never jumps, so most software stores times in UTC and only converts to local time when it shows them to a person. Pilots and the military call it "Zulu" time, which is why you'll see 1400Z written for 14:00 UTC.
Leap seconds are on their way out
Because the Earth's spin isn't perfectly even, UTC used to have an extra second slipped in now and then to stay close to it. The last one went in at the end of 2016. In 2022 the world's measurement body agreed to stop doing this by 2035, and on 15 October 2026 it voted to end leap seconds, with the change taking effect on 20 May 2027. After that, UTC simply runs on without them, though for anything official it's worth checking the current rules.
Reading an offset like "UTC+5:30"
Add five and a half hours to UTC, so when it's 12:00 UTC it's 5:30 PM in India. A minus sign works the other way round: UTC-5 is five hours behind. The Time Zone Converter does that sum for any city and date if you'd rather not.