From Greenwich to the East Coast
GMT never changes. New York is five hours behind it in winter and four hours behind it in summer. So 14:00 GMT is 9:00 AM in New York in January and 10:00 AM in July. Enter a time in the box or press Use now to see the Eastern time.
The word GMT is used loosely. The United Kingdom is on GMT only in winter; in summer it moves to British Summer Time, which is GMT plus one hour. If a UK colleague writes 3:00 PM and it is July, that is 14:00 GMT, which is 10:00 AM in New York. Check whether the time you have is really GMT or just London time.
For someone on a GMT schedule, the East Coast day starts late. The hour-by-hour table lays a 9:00 to 17:00 GMT day on the New York clock: 4:00 AM to 12:00 PM in January, and 5:00 AM to 1:00 PM in July. That puts most of the GMT working day before the East Coast starts work, and the late GMT afternoon is the shared window.
Early GMT hours belong to the previous day in New York: 3:00 AM GMT is 10:00 PM the evening before in January. The result states the date shift. Press swap to go from Eastern to GMT.
Worked examples
Questions about this tool
How many hours is EST behind GMT?
Five hours in winter. In summer, New York is on daylight time, so it is four hours behind.
Is London always on GMT?
No. London uses GMT in winter and British Summer Time, one hour ahead, in summer.
Does the gap change on the same dates as in the UK?
No. Europe and the US change clocks on different weekends, so for a few weeks a year the gap to London differs by an hour.
Related tools
Where this comes from: IANA time zone database and the rules behind it ยท RFC 6557, how the time zone database is maintained