What is the UTC standard (Coordinated Universal Time) ?

Utc Time Zone


UTC (Universal Coordinated Time) is the primary time standard by which the world regulates clocks and time.

The UTC time scale was introduced in 1972, introducing the concept of whole leap-seconds.

UTC is traditionally known as Greenwich Mean Time, GMT even if they have slight differences.


  • UTC permits a day to have 86399 seconds or 86401 seconds where necessary in order to keep the day aligned with the Sun.
  • It's the consensus international time scale with leap seconds.

Daylight Saving Time (DST)

UTC does not change with a change of seasons. The Local time may change for political or economic reasons due to daylight. See Daylight Savings Time (or DST)

Time Zone

Time zones in UTC are longitudinal time zones that are expressed in UTC using positive or negative offsets from the origin, known as UTC or Z.

Z is a reference to:

Because in the phonetic alphabet (Military) (ie Tango, Charlie, Bravo) , the Z is known as Zulu , UTC is also known as the Zulu time .

The time zone is therefore denoted:

  • or Z±HH:MM

where ±HH:MM is an offset which ranges from

  • UTC−12:00 in the west
  • to UTC+14:00 in the east

For example in the ISO string, the time zones are denoted with a Z



UTC is the timezone at the 0 offset.

Utc Time Zone

For a complete list, see World Time Zones Map



Demo of the UTC ISO string

// Now
const now = new Date(); 

// To Iso string at UTC 0
console.log('The time in the UTC+0 timezone is '+now.toISOString());

// Time to your local
console.log('Your local time is '+now.toLocaleString());
  • Result: The timezone offset in the ISO string is zero as denoted by the suffix Z


see What is a Java Instant? (Moment)

new Date().toInstant()


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