Standards
UTC vs GMT: what is the difference?
GMT is a historic mean-solar reference and modern time-zone label; UTC is the atomic international time standard.
UTC is the modern standard
Coordinated Universal Time, UTC, is the international civil time scale used to coordinate clocks worldwide. It is derived from atomic time and is kept close to Earth-rotation time through the leap-second system.
GMT has two common meanings
Greenwich Mean Time began as mean solar time at Greenwich. Today GMT is also the legal or everyday name for the UTC+0 time zone used in the United Kingdom during winter and in several other places.
For everyday conversion they show the same clock
UTC and GMT normally display the same hour and minute, so a meeting listed at 12:00 UTC is also 12:00 GMT. In technical work, UTC is preferred because it names the defined time standard rather than a regional civil-time label.