The short answer: Ireland and the UK always show the same time on the clock. In winter, both are on GMT (UTC+0). In summer, both jump to UTC+1. The UK calls that summer hour British Summer Time. Ireland calls it Irish Standard Time. Same offset, same switch dates, different label. That label is the entire source of the "Ireland time GMT WET confusion", because in Ireland the word "standard" means summer. Almost everywhere else, standard time means winter. That reversal trips up calendars, contracts, and anyone booking a July call with Dublin.
Why does Ireland call summer "standard time"?
Most countries treat daylight saving as the seasonal exception. The base state is standard time. Ireland flips that. The Standard Time Act 1968 defines Irish Standard Time as UTC+1. That is the summer offset. The winter offset, UTC+0, is simply Greenwich Mean Time under Irish law. So "standard" is the summer hour, and "GMT" is the winter hour. The terminology points the opposite way from what you would expect.
The UK does the reverse. Its Summer Time Act 1972 treats GMT as the default and British Summer Time as the seasonal adjustment. Both islands move their clocks forward on the last Sunday in March and back on the last Sunday in October. The clocks never diverge. Only the legal framing differs.
There is also the Western European Time layer. The EU classifies Ireland's winter zone as Western European Time and summer as Western European Summer Time. Irish domestic law does not use those terms, but you will see WET/WEST on some timetables and EU documents. That is technically correct at the bloc level, even though Irish statutes say GMT/IST.
When do the clocks change in Ireland?
Ireland follows the same EU schedule as the rest of the bloc. Clocks go forward on the last Sunday in March at 01:00 GMT, becoming 02:00 IST. Clocks go back on the last Sunday in October at 02:00 IST, becoming 01:00 GMT.
In January, Dublin and London both read 12:00 when GMT reads 12:00. In July, Dublin and London both read 12:00 when GMT reads 11:00. The two capitals stay locked together. The only gap is what each country calls the shared summer hour.
This matters when you schedule. Say you tell a Dublin contact "let's meet at 14:00 GMT" in July. You will be an hour early or an hour late depending on whose definition you assume. The safe rule: in summer, say "Irish time" or give the UTC offset. In winter, GMT is correct for both.
Why does Ireland have this law?
Ireland ran on Dublin Mean Time, 25 minutes and 21 seconds behind GMT, until 1916. The UK imposed GMT across the island that year as a wartime measure. After independence, Ireland kept the same clock but eventually wanted its own legal identity for time.
The 1968 Act made UTC+1 the permanent "standard" and used a separate Winter Time Order to revert to GMT for the darker months. Irish law treats winter as the exception. UK law treats summer as the exception. The practical outcome is identical. The legislative philosophy is not.
How does this differ from the UK?
For anyone checking the current time in Dublin versus London, the difference is zero. The clocks match. The problems are all in labelling, and they hit three areas hard.
Software and scheduling. The IANA time zone database gives Dublin the zone Europe/Dublin, with a summer offset of +1 and a winter offset of +0, labelled IST in summer. London gets Europe/London, same offsets, labelled BST in summer. Both work. The breakage happens when someone hardcodes "GMT" as Ireland's zone. That is wrong for half the year. A 09:00 meeting booked under "GMT" in July lands at 10:00 local in Dublin.
Broadcasting. RTÉ and the BBC both schedule in local time but announce it differently. A programme listed as "21:00 GMT" on RTÉ in July airs at 21:00 IST, which is 20:00 GMT. The BBC will say "21:00 BST". Same moment, different label. If you tune in from abroad, you need to know which label the broadcaster is using.
Contracts. Irish legal documents often specify times in GMT because that is the winter legal time. A contract spanning summer makes "GMT" ambiguous. A well-drafted Irish contract says "Irish time" or spells out "GMT (UTC+0) in winter and IST (UTC+1) in summer". The UK has the same issue with BST, but the UK's naming is more intuitive, so the errors are less frequent.
What is the simplest way to keep Ireland time straight?
Forget the names for a moment. Ireland and the UK share one clock. From late October to late March, that clock is UTC+0. Both countries call it GMT. From late March to late October, that clock is UTC+1. The UK calls that hour BST. Ireland calls it Irish Standard Time. Two names, one offset, one island group.
The word "standard" in Irish law does not mean "the usual time". It means "the time defined by the Standard Time Act", and that act happens to set the summer offset. It is a quirk of legislation. Irish people do not think of summer as "standard" and winter as "GMT". They know the clocks change with the UK and that the official summer name is different.
What about the rest of the world?
Iceland uses GMT year-round, despite sitting west of the prime meridian. Several West African nations do the same with no daylight saving: Ivory Coast, Ghana, Liberia, Guinea-Bissau, and São Tomé and Príncipe. The Canary Islands use Western European Time in winter and WEST in summer, matching Ireland's offsets under different labels.
The EU has debated ending seasonal clock changes since 2019. No decision has been implemented. Nothing has changed.
From Ireland to mainland Europe, the gap is one hour in winter (CET is UTC+1) and one hour in summer (CEST is UTC+2). To the US East Coast, the gap is five hours in January (EST is UTC-5) and four in July (EDT is UTC-4). Ireland's naming quirk does not alter any of those offsets. It only bites in the labels and in the assumptions of anyone who thinks "standard" means "the normal one".