BST vs GMT: UK time explained

The UK uses two clock times each year. Here is when each applies, what happens on the nights the clocks change, and how to avoid the classic mistakes.

Written and checked by the ExactLocalTime team at The AI Barn. Last reviewed 17 October 2026.

The short answer

GMT, Greenwich Mean Time, is UTC+0. BST, British Summer Time, is UTC+1. The UK uses GMT in winter and BST in summer. The clocks go forward one hour at 01:00 GMT on the last Sunday in March, and back one hour at 02:00 BST on the last Sunday in October. So UK clock time is GMT for about five months of the year and BST for about seven.

Exact dates

YearBST starts (clocks forward)BST ends (clocks back)
2026Sunday 29 March, 01:00 → 02:00Sunday 25 October, 02:00 → 01:00
2027Sunday 28 March, 01:00 → 02:00Sunday 31 October, 02:00 → 01:00
2028Sunday 26 March, 01:00 → 02:00Sunday 29 October, 02:00 → 01:00

These dates come from the time zone database and match the UK government's published list. The rule, the last Sunday of March and of October, is set by the Summer Time Act 1972 as amended to align with EU rules. It still applies after Brexit.

What happens on the change nights

In March, the clocks jump from 01:00 straight to 02:00. Times between 01:00 and 01:59 do not exist that night: 01:30 on 29 March 2026 never happened in the UK. You lose an hour in bed, and anything scheduled in that hour, such as a timed heating programme or a night bus timetable, needs care. The day is only 23 hours long.

In October, the clocks go back from 02:00 to 01:00, so the hour from 01:00 to 01:59 happens twice, once on BST and once on GMT. "01:30 on 25 October 2026" is ambiguous unless you say which. Overnight shift workers may work an extra hour, and logs that record local time can appear to go backwards. The day is 25 hours long.

Smartphones, computers and most connected devices change automatically. Cookers, car dashboards, older central heating timers and many wall clocks do not.

Why the UK has summer time

The idea is usually credited to the builder William Willett, who campaigned from 1907 for moving clocks forward in summer so that evenings would be lighter. Willett died in 1915, and Britain adopted summer time the following year, in May 1916, under wartime pressure to save fuel. Germany had done the same a few weeks earlier. Summer time has been used every year since, with variations. During the Second World War the UK used British Double Summer Time (UTC+2) in summer and BST in winter. From 1968 to 1971, as an experiment, it stayed on UTC+1 all year, then called British Standard Time. The experiment ended partly because of complaints about dark winter mornings in Scotland and northern England.

The debate continues. Supporters of permanent BST point to lighter evenings. Opponents point to sunrise after 09:00 in parts of Scotland in midwinter. There are no current government plans to change the system.

BST is not "London time all year"

The most common mistake is to use "GMT" as the name for UK time all year round. In summer, a time quoted in GMT is an hour behind UK clocks: "Kick-off 15:00 GMT" in August means 16:00 in London. Some international organisations do this deliberately, because they really mean UTC+0. Others get it wrong. If you are writing a time for people in the UK, say "UK time". If you mean the zero offset, say "UTC".

The reverse mistake is rarer but happens: describing a winter time as "BST". From late October to late March there is no BST in the UK.

In software, avoid storing "GMT" or "BST" at all. Use the zone name Europe/London, which carries both rules and the exact change dates.

How BST affects time differences

  • Europe: EU countries change at the same instant as the UK (01:00 UTC), so the UK stays one hour behind Paris, Berlin and Madrid, and two hours behind Athens and Helsinki, all year. Ireland and Portugal stay level with the UK.
  • North America: the US and Canada change on different dates: the second Sunday of March and the first Sunday of November. The usual 5-hour gap between London and New York drops to 4 hours for a few weeks: in 2026, from 25 October to 1 November; in 2027, from 14 to 28 March and from 31 October to 7 November. See BST vs EST.
  • Places with no clock changes: the gap changes only when the UK changes. Dubai is 4 hours ahead of the UK on GMT and 3 hours ahead on BST. India is 5½ and 4½ hours ahead. Japan is 9 and 8.
  • Southern hemisphere: Australia and New Zealand change in the opposite direction, so the gap swings by two hours over the year. Sydney is 11 hours ahead in the UK winter and 9 in the UK summer, with short spells of 10 hours in between.

How to write UK times clearly

  • Write "UK time" or "London time" for local clock time, all year.
  • Write "BST" only between the last Sunday of March and the last Sunday of October, and "GMT" only outside it.
  • For international readers, add the offset: "14:00 UK time (UTC+1)".
  • Around the change dates, always include the date, and for times in the October repeated hour, say whether you mean BST or GMT.
  • Calendar invitations should be created in the Europe/London zone, so they move correctly for overseas guests.

Tools

See the current UK time, with the correct BST or GMT label, on our London page. Convert a UK time on a specific date with the time zone converter. The BST and GMT pages have more on each, and GMT vs UTC explains how GMT relates to atomic time.

Sources