Time zones are regions based on GMT or Greenwich Mean Time which is ultimately the time zone at the zero degrees longitude. Use the Time Zone Calculator to determine the time of a certain region given the current time of another region based on the GMT or Greenwich Mean Time. This Time Zone Calculator is, in fact, works as a time converter. All you need to do is mention the date, time, a base GMT, and a targeted GMT to which you want to convert the base time. Note that, daylight saving time is not considered by this Time Zone Calculator.