| Light Blue | Western European Time / Greenwich Mean Time (UTC) |
| Blue | Western European Time / Greenwich Mean Time (UTC) |
| Western European Summer Time / British Summer Time / Irish Standard Time (UTC+1) | |
| Red | Central European Time (UTC+1) |
| Central European Summer Time (UTC+2) | |
| Yellow | Eastern European Time / Kaliningrad Time (UTC+2) |
| Ochre | Eastern European Time (UTC+2) |
| Eastern European Summer Time (UTC+3) | |
| Green | Moscow Time / Turkey Time (UTC+3) |
| Turquoise | Armenia Time / Azerbaijan Time / Georgia Time / Samara Time (UTC+4) |
▉▉▉ Dark colours: Summer time observed
Ireland uses Irish Standard Time (IST, UTC+01:00; Irish: Am Caighdeánach Éireannach) in the summer months and Greenwich Mean Time (UTC+00:00; Irish: Meán-Am Greenwich) in the winter period.[1]
Roughly two-thirds of the Republic is located west of the 7.5°W meridian. Thus the local mean time in most of Ireland is closer to UTC-01:00 time than to GMT. The Standard Time Act 1968 legally established that "the time for general purposes in the State (to be known as standard time) shall be one hour in advance of Greenwich mean time throughout the year".[2] This act was amended by the Standard Time (Amendment) Act 1971, which legally established Greenwich Mean Time as a winter time period.[1] Ireland therefore operates one hour behind its statutory standard time during the winter period, and reverts to standard time in the summer months. This definition contrasts with the practice of other states in the European Union, which operate one hour ahead of their standard time during the summer period, but produces the same result. The net effect is that time in Ireland is the same as that in Portugal and the United Kingdom.
The instant of transition to and from daylight saving time is synchronised across Europe. In Ireland, winter time begins at 02:00 IST on the last Sunday in October (changing the clocks to 01:00 GMT), and ends at 01:00 GMT on the last Sunday in March (changing to 02:00 IST).[3][4]
The following table lists recent past and near-future starting and ending dates of Irish Standard Time or Irish Summer Time (use of DST beyond 2019 is under discussion, see below):
| Year | Start | End |
|---|---|---|
| 2021 | 28 March | 31 October |
| 2022 | 27 March | 30 October |
| 2023 | 26 March | 29 October |
| 2024 | 31 March | 27 October |
| 2025 | 30 March | 26 October |
| 2026 | 29 March | 25 October |
| 2027 | 28 March | 31 October |
| 2028 | 26 March | 29 October |
- ^ a b Standard Time (Amendment) Act, 1971
- ^ Standard Time Act, 1968
- ^ "Topical Issue Debate – Daylight Saving Time". Dáil Debates. 26 October 2011. p. 19.
- ^ "S.I. No. 506/2001 – Winter Time Order, 2001". 24 October 2001.