EST, EDT and GMT
Eastern Standard Time (EST) is 5 hours behind GMT. From the second Sunday in March to the first Sunday in November the US East Coast uses Eastern Daylight Time (EDT), which is 4 hours behind. People often say EST all year, so the safest way is to enter the actual date: the converter picks the right offset automatically.
GMT and UTC are the same for everyday purposes. London uses GMT in winter but British Summer Time (UTC+1) in summer, so add London as a city if you need the UK time rather than UTC.
Typical uses
Webinars, stock market hours, server logs and flight times are often given in Eastern Time or UTC. Enter the time once and see both side by side, along with any other cities you add.