Editing Greenwich Mean Time

{{Short description|Historical time standard associated with UTC+0}}

'''Greenwich Mean Time''' ('''GMT''') is a time standard historically based on mean solar time at the Royal Observatory in Greenwich, London. It is associated with the [[UTC+0]] offset and is commonly used as a civil time reference in places that use no offset from [[Coordinated Universal Time]].<ref name="utc-gmt"/><ref name="utc0-use"/>

In modern timekeeping, [[Coordinated Universal Time]] is the main reference used for international time-zone offsets. GMT remains in use as a named time standard, especially in ordinary civil, geographic, and historical contexts.<ref name="time-zone-utc"/>

== Use ==
Greenwich Mean Time is used as standard time in areas that follow UTC+0 during part or all of the year. It is most often associated with the United Kingdom and nearby Atlantic and western European timekeeping traditions.

In countries that observe daylight saving time, GMT may be used during the standard-time period before clocks move forward by one hour. When daylight saving time is active, the local time may change to a UTC+1 offset.

== Relationship with UTC ==
GMT and UTC+0 have the same clock reading in ordinary civil use. When it is 12:00 UTC, the local time under GMT is also 12:00.

UTC is the modern technical standard for coordinated timekeeping. GMT is used more often as a named civil time and historical reference.

== Time calculation ==
Greenwich Mean Time applies no hour offset from UTC. The local time remains the same as Coordinated Universal Time.

For example, 08:00 UTC is 08:00 GMT. 23:00 UTC remains 23:00 GMT.

== See also ==
* [[Coordinated Universal Time]]
* [[UTC+0]]
* [[UTC+1]]
* [[Time zone]]
* [[Daylight saving time]]

== References ==
{{Reflist|refs=
<ref name="utc-gmt">"[[Coordinated Universal Time#Relationship to other time scales|Relationship to other time scales]]". ''Coordinated Universal Time''. ''Vrienden Universe Wiki''. Section describing GMT as a historical time reference and UTC as the modern standard for most civil and technical use. Accessed 15 June 2026.</ref>
<ref name="time-zone-utc">"[[Time zone#Relationship with UTC|Relationship with UTC]]". ''Time zone''. ''Vrienden Universe Wiki''. Section describing UTC as the main reference point for time-zone offsets. Accessed 15 June 2026.</ref>
<ref name="utc0-use">"[[UTC+0#Use|Use]]". ''UTC+0''. ''Vrienden Universe Wiki''. Section connecting UTC+0 with Greenwich Mean Time and Western European standard time. Accessed 15 June 2026.</ref>
}}

[[Category:Time zones]]
[[Category:UTC offsets]]