Time in the Danish Realm

Denmark, including its dependencies of Faroe Islands and Greenland, uses six time zones.

Central European Time
UTC+01:00 as standard time, and UTC+02:00 as daylight saving time, with transition dates according to the European Union rules.
 * All of Denmark proper.
 * Including Copenhagen, Aarhus and Rønne (Bornholm)
 * The UTC+01:00 centerline (15°E) goes through Bornholm, approximately 2 kilometers from Gudhjem, in the far eastern Denmark, while Copenhagen at 12°34′E corresponds to UTC+0:50, and the west coast at 8°6′E corresponds to UTC+0:32.
 * An 1893 law set the de jure standard time of Denmark as the mean solar time 15°E of Greenwich, for all of Denmark, with an exception for the Faroe Islands, effective at 1 January 1894. This linked the standard time in Denmark to Earth's rotation, and clocks in Denmark were at 12:00, when the sun is directly above the 15° Eastern meridian. As Earth's rotation is not completely regular, the time could be offset by up to 0.9 seconds in either direction, compared to UTC+1, requiring a leap second to be added to remedy the issue. On 14 March 2023, the Folketing adopted a proposal to set the de jure standard time of Denmark as UTC+1, with exceptions made for Greenland and the Faroe Islands. The proposal became effective law on 26 March 2023 at 2:00, superseding the 1893 law.

Western European Time
UTC±00:00 as standard time, and UTC+01:00 as daylight saving time.
 * The Faroe Islands
 * The island of Mykines is actually located at 7°36′W longitude and thus at UTC-00:31 (closer to UTC-01:00 than UTC), however Mykines uses the same time zone as the rest of the Faroe Islands.

Greenwich Mean Time
UTC±00:00 year around, no daylight saving time
 * The northeast coast of Greenland. There are a few settlements, like the weather station Danmarkshavn, otherwise unpopulated.
 * The area uses same time as Iceland (WET), since it is generally supplied from Iceland. This is however unofficial. In the summer the time is the same as for East Greenland time.

West Greenland Time
UTC-02:00 as standard time, and UTC-01:00 as daylight saving time.
 * All the west coast of Greenland
 * Including Qaanaaq, Ilulissat, Kangerlussuaq, Nuuk and Qaqortoq
 * Tasiilaq, Kulusuk, Ittoqqortoormiit, Neerlerit Inaat and surrounding area on the east coast
 * Except Pituffik Space Base
 * Some places, such as Qaanaaq (69°13′W corresponding to UTC-04:37) and Kulusuk (37°11′W corresponding to UTC-02:28) are located outside the UTC-03:00 ± 00:30 zone, but still use the same time zone as the capital Nuuk (51°44′W corresponding to UTC-03:26:56)

Atlantic Time
UTC-04:00 as standard time, and UTC-03:00 as daylight saving time, with transition dates according to the United States rules.
 * Pituffik Space Base

Daylight saving time
All of Greenland uses Daylight Saving Time, except for the northeast coast. The transition dates are according to the European Union rules, except for the Pituffik Space Base, which uses United States transition dates and for which the following description does not apply.

DST starts at 01:00 UTC on the last Sunday in March and ends same time on the last Sunday in October each year in all affected areas.

That means that in Denmark proper, the transition is at 02:00 Local Standard Time (03:00 Daylight Saving Time) and in the Faroe Islands one hour earlier. In most of Greenland, the transition takes place at 23:00 Local Standard Time on the day before (00:00 Daylight Saving Time).

History
The first time a common time was used in Denmark, was in 1890, when Copenhagen local time was used as railway time. This was GMT+0:50:20 from Greenwich. In 1890 this time was introduced as a standard time for Denmark. In 1893, Denmark adopted the "Act on the Determination of Time", to connect to the international time zones, using Greenwich plus one hour, which set the standard time in Denmark as 12:00 when the sun is directly above 15°E, starting from 1 January 1894. This is the local time of eastern Bornholm, leaving 99.5% of the country west of the time meridian (15°E), which has triggered some sarcastic comments (changing from Copenhagen time to Gudhjem time). However all of the country is located east of Greenwich +00:30 (7.5°E).

Daylight saving time was used in the years 1916, 1940, 1945-1948 and is used from 1980.

The Faroe Islands introduced Greenwich Mean Time in 1908, and Iceland (then a Danish area) introduced GMT-01:00 at the same time (changed to GMT, permanent daylight saving time, in 1968). West Greenland introduced GMT-03:00 in 1916. Daylight saving time was introduced in the Faroe Islands in 1981.

On 25 January 2023, Transport Minister, Thomas Danielsen made a proposal to overrule the 1893 law, with an act to set Danish standard time as UTC+1, with exceptions for Greenland and the Faroe Islands. On 14 March 2023, the Folketing adopted the proposal with unanimous consent, and the proposal came in effect as law on 26 March 2023, at 2:00. Greenland moved the time zone forward one hour simultaneously (on 25 March 2023 local time), after that using UTC-02:00 as the standard time.

IANA time zone database
Data for Denmark directly from zone.tab of the IANA time zone database. Columns marked with * are the columns from zone.tab itself.