The Two Faces of London Time
Assume London is on BST for seven months of the year. That is the default answer to "What time is it in London?" for most of the calendar. The exception is anyone scheduling a transatlantic call in November, December, or January, when GMT is the safe assumption.
GMT is the winter setting, locked to UTC+0. When London runs on GMT, the clocks at the Royal Observatory in Greenwich read the same as Coordinated Universal Time. BST is the summer setting, UTC+1. The city jumps one hour ahead of the UTC standard.
The practical rule: London is on BST from the last Sunday of March to the last Sunday of October. The rest of the year, it is on GMT.
What the One-Hour Shift Does to Global Time Gaps
The difference is exactly sixty minutes. That single hour reshapes every time gap London has with the world.
On 15 January 2026, with London on GMT, New York is 5 hours behind, Dubai is 4 hours ahead, and Sydney is 11 hours ahead. On 15 July 2026, with London on BST, Dubai drops to 3 hours ahead, Sydney to 9 hours ahead, and São Paulo widens from 3 hours behind to 4 hours behind.
The offset change is not symmetrical. Some cities keep their own daylight saving schedules, so the gap between London and New York can stay at 5 hours year-round, while the gap between London and Sydney varies between 9 and 11 hours.
When London Switches
The switch runs on fixed rules, not fixed dates.
Book the last Sunday of March. At 01:00 GMT, clocks jump forward. That 01:00 becomes 02:00 BST. In 2026, that is Sunday 29 March. In 2027, it is Sunday 28 March.
Book the last Sunday of October. At 02:00 BST, clocks fall back. That 02:00 becomes 01:00 GMT. In 2026, that is Sunday 25 October. In 2027, it is Sunday 31 October.
The daylight swing is extreme. On the December solstice, 21 December 2026, London gets 7 hours 50 minutes of daylight: sunrise at 08:03, sunset at 15:53. On the June solstice, 21 June 2026, London gets 16 hours 39 minutes: sunrise at 04:42, sunset at 21:21.
How the Seasons Hit the Clock
| Period | Time Offset | Dates | What You Get |
|---|---|---|---|
| Winter (GMT) | UTC+0 | Late October to late March | Sunrise after 08:03 on the solstice, sunset before 15:53 |
| Summer (BST) | UTC+1 | Late March to late October | Long evenings, sunset at 21:21 on the solstice |
| Transition (March) | Forward shift | Last Sunday of March | One hour of sleep lost, lighter evenings begin |
| Transition (October) | Backward shift | Last Sunday of October | One hour of sleep gained, darker evenings return |
The March equinox gives London sunrise at 06:05 and sunset at 18:11. The September equinox gives sunrise at 06:44 and sunset at 19:01. The switch days themselves are more abrupt: the last Sunday of March yanks sunset an hour later overnight, and the last Sunday of October shoves it an hour earlier.
Scheduling Without the One-Hour Mistake
The most common error is treating "GMT" as a permanent label for London time. A meeting set for "3 PM GMT" in July happens at 4 PM BST. You miss the call. You arrive at the gate after departure. You tune into the live stream an hour late.
The abbreviation BST causes its own pile-up. BST also means Bangladesh Standard Time (UTC+6) and Bougainville Standard Time (UTC+11). A colleague in Dhaka who says "meet at 10:00 BST" means 10:00 Bangladesh time, which is 04:00 London time in winter and 05:00 London time in summer. Always confirm the time zone by full name, not the abbreviation.
For flights: check whether London is on GMT or BST on your departure date. Use the last Sunday of March and the last Sunday of October as your cut points. Departing 30 March 2026, the day after the spring change? London is on BST. Departing 24 October 2026, the day before the autumn change? London is still on BST.
For transatlantic calls: the UK and the US do not change clocks on the same dates. The UK changes on the last Sunday of March and October. The US changes on the second Sunday of March and the first Sunday of November. That creates a few weeks each year where the London, New York gap is off by one hour from the usual 5 hours. Check the exact date.
For London, Sydney calls: the overlap is brutal. A London evening slot of 18:00 to 20:00 catches Sydney at 04:00 to 06:00. Reserve this window for urgent calls only.
For London, Tokyo or London, Singapore calls: aim for 07:00 to 09:00 London time. That catches the late afternoon, 15:00 to 17:00, in Tokyo and Singapore.
For London, Dubai calls: a 3- to 4-hour overlap sits across most of the London working day. Schedule anytime between 09:00 and 16:00 London time.
The "Spring Forward, Fall Back" Mnemonic
In spring, clocks spring forward by one hour. In autumn, clocks fall back by one hour.
"Spring forward" means losing an hour of sleep on the last Sunday of March. "Fall back" means gaining an hour on the last Sunday of October.
The mnemonic works in the UK, the US, Canada, and most of Europe. It fails in the Southern Hemisphere, where spring and autumn are reversed. In Sydney, clocks go forward in October and back in April. Anyone crossing hemispheres should ignore the mnemonic and use the date rule: last Sunday of March forward, last Sunday of October back.