UK and US Time Difference: Calls Between London and America

Last updated October 11, 2026

The whole UK runs on one clock, London time, but the 50 US states span six time zones, so the gap depends on where the American side is. It also moves for a few weeks each year, because the two countries change their clocks on different Sundays.

The time difference by US city

The UK uses Greenwich Mean Time (GMT, UTC+0) in winter and British Summer Time (BST, UTC+1) in summer. England, Scotland, Wales and Northern Ireland all share it. Most of the US also moves its clocks by an hour in summer, so for most of the year the gap to each US zone stays the same. Arizona (except the Navajo Nation) and Hawaii stay on standard time, so their gap is one hour bigger while the UK is on BST.

The last column counts the hours when a normal 9-to-5 day overlaps in both cities. The East Coast gets three hours. Chicago gets two and Denver one. Between London and California there is none, so one side has to start early or stay late.

The weeks when the gap is four hours

US daylight saving time starts on the second Sunday in March and ends on the first Sunday in November. In the UK it starts on the last Sunday in March and ends on the last Sunday in October. In spring the US changes first and the gap shrinks to four hours until the UK catches up. In autumn the UK changes first, and the gap is four hours for one week until the US follows.

The same thing happens with every US city that changes its clocks. Chicago is five hours behind London in those weeks instead of six, and Los Angeles seven instead of eight. Phoenix and Honolulu do not change their clocks, so their gap to London moves only on the UK dates.

Best times for a call

• From the East Coast, 9 a.m. to noon Eastern is 2 to 5 p.m. in London. A 10 or 11 a.m. call leaves both sides some room at either end of the day.
• From the Midwest, 8 to 11 a.m. Central is 2 to 5 p.m. in London. A 9 a.m. Central call, at 3 p.m. in London, sits in the middle of that window.
• From the West Coast there is no shared office time. A call at 8 a.m. Pacific is 4 p.m. in London. If the UK side can stay to 6 p.m., the US side gets until 10 a.m.

A request sent from the US on Friday afternoon reaches London on Friday evening, after most people have gone home for the weekend. Holidays differ too. The Fourth of July and Thanksgiving are normal working days in the UK, and Boxing Day (December 26) and the August bank holiday are normal working days in the US.

Recurring meetings around the clock changes

A weekly call is fixed in the time zone of the person who created it. If a New York manager sets it for 11 a.m. Eastern, it shows as 4 p.m. in London most weeks and 3 p.m. during the four-hour weeks. If a London colleague sets it for 4 p.m. UK time, the US side sees it move to 12 noon instead of 11 a.m. Neither calendar is wrong, but people turn up an hour early or late when they forget.

Before the March and October dates, send a short note to the group saying which side keeps the fixed time. Writing both times in the invitation helps: "11:00 a.m. ET / 4:00 p.m. UK".

GMT, BST, EST and EDT

Abbreviations cause many of the mistakes. In summer, London is on BST, not GMT, even though many people say "GMT" all year. New York is on EST only in winter and on EDT from March to November. An invitation that says "3 p.m. GMT" in July is one hour off for London if the reader takes it literally. Write "London time" or "UK time" instead, or use the UTC offset. The guide to time zone abbreviations lists the common pairs.

To test a date, open the Meeting Planner with London and New York, Chicago or Los Angeles. The daylight saving time guide has the clock change dates for both countries, and the overlapping business hours guide compares London with other cities.

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