Travelmath provides an online time zone converter for places all over the world. You can enter airports, cities, states, countries, or zip codes to find the time difference between any two locations. The calculator will automatically adjust for daylight saving time (DST) in the summer. You can use it as a meeting planner or a scheduler to find the best time to make international phone calls. World time zones have a positive or negative offset computed from Coordinated Universal Time (UTC), or Greenwich Mean Time (GMT). UTC has uniform seconds defined by International Atomic Time (TAI), with leap seconds announced at irregular intervals to compensate for the Earth's slowing rotation. The tz database or zoneinfo database uses the closest city, rather than the more common Eastern, Central, Mountain or Pacific time zones in the United States. Countries often change their daylight saving rules, so please help us stay current by letting us know if you find any pages that need updates.