Time Difference: New York & London

The time difference between New York and London is crucial, especially for the financial service sector. For most of the year, London is 5 hours ahead of New York. However, while both areas observe daylight saving in summer, the onset and ending dates aren't exactly aligned, causing a shift in the time difference for moments in the spring and fall.

In the United States, daylight saving begins on the second Sunday in March, and lasts until the first Sunday in November. In Britain, it begins on the last Sunday in March, and lasts until the last Sunday in October. So in all, daylight saving in London begins later, and ends earlier. During those gap periods, New York is only 4 hours behind London, as opposed to the 5 hour difference, when both cities are on daylight saving or when both cities are off. Because there isn't a moment at which London is on and New York is off daylight saving, the London - New York time difference will never be 6 hours.

In conclusion, the time difference between New York and London is as follows:

• First Sunday in November - second Sunday in March: 5 hour (both off DST)
• Second Sunday - last Sunday in March: 4 hour
• Last Sunday in March - last Sunday in October: 5 hour (both on DST)
• Last Sunday in October - first Sunday in November: 4 hour

Sources:

• http://wwp.greenwichmeantime.com/time-zone/rules/usa/
• http://wwp.greenwichmeantime.com/info/bst.htm