What Is UTC Time?

UTC, or Coordinated Universal Time, is the time standard the world sets its clocks by. Every time zone is described as an offset from it: UTC+9 for Tokyo, UTC−5 for New York in winter. UTC itself never changes for daylight saving, so it's a stable reference point all year round.

How UTC is kept

UTC comes from atomic clocks in laboratories around the world, whose readings are combined under the coordination of the International Bureau of Weights and Measures. Your phone and computer get their time from servers that trace back to these clocks.

UTC and GMT

GMT, or Greenwich Mean Time, began as the mean solar time at the Royal Observatory in Greenwich, London. In everyday use, GMT and UTC show the same time, and people often use the two interchangeably. Technically, GMT is based on Earth's rotation and UTC on atomic clocks. GMT is also the name of a time zone used in winter by the UK and others, and those places aren't on GMT in summer. So "UTC" is the clearer choice when you need precision.

Why the odd abbreviation?

English speakers proposed CUT for "Coordinated Universal Time", and French speakers proposed TUC for "Temps Universel Coordonné". UTC was the compromise, and it matched neither language.

Leap seconds

Atomic time is steadier than Earth's rotation, so the two slowly drift apart. Since 1972, occasional leap seconds have kept them within a second of each other. They cause problems for computer systems, and in 2022 international measurement authorities voted to stop adding them by 2035.

Why it matters to you

UTC is useful whenever more than one time zone is involved. Programmers store times in UTC and convert them for display, and pilots use it so everyone agrees on the time. To turn it into your local time, try our time zone converter.