London is one of the world's most important time zone reference points — it's home to the Greenwich Prime Meridian, the historical origin of global timekeeping. Whether you're scheduling a call with a London colleague, watching a live event, or just curious what time it is in the UK right now, this guide has everything you need.
What time zone is London in?
London uses two time zones depending on the time of year:
- GMT (Greenwich Mean Time) — UTC+0 — used from late October to late March
- BST (British Summer Time) — UTC+1 — used from late March to late October
The UK switches to BST on the last Sunday of March (clocks go forward 1 hour) and back to GMT on the last Sunday of October (clocks go back 1 hour). The phrase used to remember this is "spring forward, fall back".
London time vs major world cities
Here's London's time difference from major global cities (in winter, when London is on GMT):
- New York: London is 5 hours ahead
- Los Angeles: London is 8 hours ahead
- Dubai: London is 4 hours behind
- Mumbai: London is 5.5 hours behind
- Singapore: London is 8 hours behind
- Tokyo: London is 9 hours behind
- Sydney: London is 10-11 hours behind
These differences shift by 1 hour when the UK is on BST (summer) and when other countries change their clocks.
Best times to call London from the US
The sweet spot for calling London from the US East Coast is 9 AM–1 PM Eastern Time — which corresponds to 2–6 PM London time in winter. Both parties are well into their working day.
From the US West Coast, the window is tighter: 8–11 AM Pacific Time = 4–7 PM London. Anything after 11 AM Pacific is after 6 PM in London — most people have finished work.
For a precise overlap finder, use our Meeting Planner — select your city and London to see the exact best meeting windows right now.
London and the Prime Meridian
London's central role in world timekeeping is no accident. The Royal Observatory in Greenwich — now a suburb of London — was established in 1675 to improve navigation for British ships. In 1884, at the International Meridian Conference in Washington DC, Greenwich was chosen as the location of the Prime Meridian (0° longitude) by a vote of 25 nations.
From that decision, Greenwich Mean Time became the world's reference time — and London became the literal center of global timekeeping. UTC, which replaced GMT as the official world standard in 1960, is still anchored to Greenwich's longitude.