In the graph below you see the time zone difference between Greenwich Mean Time and Eastern Standard Time. Drag the bubble to adjust the time and to see the corresponding time in the other time zone.
Greenwich Mean Time is the time zone of the 0 meridian, located in London, United Kingdom, including cities like London, Lisbon and Dublin (in the winter). Eastern Standard Time is the time zone of the Canadian and US East Coast, with places like Montreal, Ottawa, New York, Washington D.C. And Miami.
Usually it is preferable to schedule meetings in the afternoon for the person in GMT and before lunch for the person in EST.
GMT, or Greenwich Mean Time, is the zero when it comes to time zones – they are all counted from the zero meridian that runs through the village of Greenwich.
While both the UK and Portugal are officially on GMT you need to pay attention to whether they are actually observing it or are using their own. Britain in the summer for example use British Summer Time – which is different than GMT.
London, Lisbon, Dublin, Edinburgh
GMT does not observe DST as it is the zero hour time zone – it never changes.
This is the standard time of the Eastern US, Canada and parts of the Caribbean. It is in most places observed only in the winter months, from November to March. The origin of EST is the same as for most time zones – it was introduced when the railroad was built across the United States. It is important to note that there is also Eastern Standard Time in Australia, but this is usually called AEST and thus not to be confused with EST.
Most of the Eastern seaboard of the US observe EST, as well as most locations in Eastern Canada although there are a few exceptions. Locations such as New York, Washington, Quebec and Ontario are all on Eastern Standard Time. Also some Caribbean locations such as Jamaica, Haiti and Panama are in this time zone.
It is important to note that with the exception of Panama, Jamaica and a couple of locations in Canada and the US most in this time zone do observe DST and thus switch to EDT in the summer. As always, it is better to look up the actual location than the timezone itself.