For practical purposes they are same. GMT is Greenwich Mean Time. It is related to how the earth rotates but in practice Atomic clocks are used to measure it. UTC is universal time coordinated set by the average of a number of atomic clocks.How many hours is est behind UTC?
When planning a call between EST and UTC, you need to consider time difference between these time zones. EST is 5 hours behind of UTC. If you are in EST, the most convenient time to accommodate all parties is between 9:00 am and 1:00 pm for a conference call or meeting. In UTC, this will be a usual working time of between 2:00 pm and 6:00 pm.