GMT stands for Greenwich Mean Time. It is the yearly average time each day when the Sun crosses the Prime Meridian at the Royal Observatory in Greenwich, London. For many years, it was used as the global standard for telling time.
UTC stands for Coordinated Universal Time. It is the modern, highly precise time standard used globally today to keep all clocks synchronized. While it shares the same time as GMT, UTC is kept incredibly exact using highly precise atomic clocks around the world.
Because the Earth rotates, different parts of the world experience sunlight at different times. To keep things organized, the Earth is divided into 24 main vertical sections known as time zones. Time zones ensure that "noon" happens when the sun is roughly at its highest point in the sky, no matter where you live.
To find the time difference between two places, you can compare their UTC offsets. For example, if City A is UTC+2 and City B is UTC+5, City B is exactly 3 hours ahead of City A. Our website's "Compare Time" tool handles all of this math for you automatically!
Countries have different times so that their local clock matches the position of the sun in their sky. Without time zones, a single global time would mean some countries might experience "morning" at 3:00 PM while it is completely dark outside!
Daylight Saving Time (DST) is the practice of moving the clock forward by one hour during the warmer months. This shifts sunlight from the early morning to the evening, giving people an extra hour of daylight after work or school. Not all countries observe DST.