Ireland is on Irish Standard Time

Ireland keeps one zone, Europe/Dublin, and it takes two values across the year. In winter it is Greenwich Mean Time, UTC+0. In summer it is Irish Standard Time, UTC+1. The clocks next change on Sunday 25 October 2026, when 02:00 becomes 01:00. There is no separate zone for Northern Ireland: the whole island keeps the same time all year.

For about five months of the year, yes: from the last Sunday in October to the last Sunday in March. For the other seven it is an hour ahead of GMT, on Irish Standard Time. The confusion is understandable: the IANA database still names Ireland's zone "Greenwich Mean Time" even while the country is running an hour ahead of it, and the clock at the top of this page will tell you which of the two applies right now.

Greenwich Mean Time is mean solar time at the Greenwich meridian, zero degrees longitude, and it is the reference every other zone is counted from. In practice UTC has replaced it as the technical standard (UTC is kept by atomic clocks rather than by the sun), but the two never differ by more than a second and the names are used interchangeably outside astronomy.

26 distinct offsets are in use across the 275 cities on this site, running from UTC-07:00 to UTC+13:00. The full range is wider still, from UTC-12 to UTC+14, and they are not all whole hours: India, Iran and Newfoundland run on the half hour, Nepal and the Chatham Islands on the quarter.

No. 32 of the 235 countries and territories on the map keep more than one, which is why the map labels those by how many clocks they keep rather than picking one. France has the most of any country once its overseas territories are counted; China is the opposite case, spanning five geographic zones and running all of them on a single clock.

Because zone abbreviations were never standardised and several were claimed twice. IST is Irish Standard Time (UTC+1), India Standard Time (UTC+5:30) and Israel Standard Time. CST is worse: it is Central Time in North America, China Standard Time and Cuba Standard Time. If a time matters, use the UTC offset or the IANA zone name rather than the abbreviation.