Greenwich/British Summer (GMT/BST)
London operates on Greenwich/British Summer (GMT/BST). London observes summer time (DST), shifting clocks forward one hour in March and back in October.
Time Zone: Greenwich Mean Time / British Summer Time — Standard Offset: UTC+0 (GMT) — DST Offset: UTC+1 (BST)
Country: United Kingdom
This city observes Daylight Saving Time, so the UTC offset changes twice per year. Always verify the current offset when scheduling across time zones.
London holds a unique position in global timekeeping as the home of the Prime Meridian at the Royal Observatory in Greenwich. Greenwich Mean Time (GMT) serves as the baseline reference for every other time zone on Earth — all offsets are measured as hours ahead of or behind GMT. While UTC (Coordinated Universal Time) has technically replaced GMT as the world standard, the terms are often used interchangeably for civilian purposes. London sits at the literal center of world time.
The London Stock Exchange opens at 8:00 AM GMT and closes at 4:30 PM GMT. London's time zone creates a crucial overlap window with both Asian and American markets. From roughly 8:00 AM to 9:00 AM GMT, London overlaps with the tail end of Asian trading. From 1:00 PM to 4:30 PM GMT (when New York opens at 9:30 AM ET), London overlaps with US markets. This overlap period sees the highest forex trading volumes globally — over 43% of all global foreign exchange transactions pass through London.
The UK switches to British Summer Time (BST) on the last Sunday in March, moving clocks forward one hour to UTC+1. Clocks fall back to GMT on the last Sunday in October. Because the UK and US change their clocks on different dates, the time difference between London and New York fluctuates: it's normally 5 hours, but drops to 4 hours for a few weeks in late March (when the US has already sprung forward but the UK hasn't yet) and again in late October.
London time makes it a natural hub for international teams. A 9 AM meeting in London catches Hong Kong at 5 PM (end of their business day), Dubai at 1 PM, and New York at 4 AM (too early). The sweet spot for London-to-US calls is typically 2 PM to 5 PM GMT, which catches the East Coast at 9 AM to 12 PM. For London-to-Asia coordination, morning meetings in London work best — 8 AM GMT is 4 PM in Hong Kong and 5 PM in Tokyo.