In the graph below you see the time zone difference between Mountain Daylight Time and Eastern Daylight Time. Drag the bubble to adjust the time and to see the corresponding time in the other time zone.
Mountain Daylight Time is the time zone of the US and Canadian states around the Rocky Mountains, including cities like Edmonton, Calgary, Denver and Salt Lake City. Eastern Daylight Time is the time zone of the Canadian and US East Coast when observing daylight saving time in the summer, with places like Montreal, Ottawa, New York, Washington D.C. And Miami.
Usually it is preferable to schedule meetings in the morning for the person in MDT and after lunch for the person in EDT.
MDT is observed in the Western part of central US and Canada, as well as the North West corner of Mexico. It is 6 hours behind UTC and turns into MST in the summer. In Mexico, this time zone is known as Zona Pacifico (Pacific Zone). The name Mountain Daylight Time comes from it covering the Rocky Mountains in Western United States.
In the US, Arizona, Colorado, Montana, Utah, New Mexico and Wyoming are all observing Mountain Daylight Time but there is also a bunch where part of the state observe MDT and part another time zone, like CDT or PDT.
MDT is observed in parts of Canada, the US and Mexico. The only province in Canada to be fully covered by MDT is Alberta whereas other provinces like British Columbia and Northwest Territories are split between MDT and PDT.
In Mexico, it is only the states in the north western corner of the country, including Baja California, Sinaloa and Chihuahua that observe MDT.
The largest city observing Mountain Daylight Time is Phoenix, followed by Denver and El Paso/Juarez.
MDT is observed in almost all locations that observe Mountain Time, except the states of Arizona (US) and Sinaloa (Mexico). DST is in effect between March and November and adds one hour time difference to UTC.
This is the summer time of the Eastern US, Canada and parts of the Caribbean. It is in effect between March and October for most locations and is four hours behind UTC. It is important to note that even within certain states, e.g. Florida, Michigan, and Tennessee there are locations that do NOT observe EST/EDT but instead belong to other time zones. The same goes for the Canadian provinces Ontario and Quebec.
Most of the Eastern seaboard of the US observe Eastern Daylight Time, 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.
With the exception of Panama, Jamaica and a couple of locations in Canada and the US daylight saving time is observed. Unless you are sure that the location you have in mind is truly in EST/EDT it is always better to use the exact location name rather than the time zone abbreviation.