I intentionally tried to keep the spreadsheet as simple as possible, so I didn't account for the time that DST starts (typically 2:00 am), and the rules only work for a single year (which is why I have a note about the planner not working for meetings spanning multiple years). There may be exceptions to that in reality, but they are rare, so I stuck with this assumption for now.

There are even different rules for locations within a main time zone, such as Arizona.Įach rule defines the dates that DST begins and ends, and if a location is ON DST, then it is assumed that 1 hour is added to the UTC offset. The complexity of time zone conversion comes from Daylight Saving Time (DST) rules, which are different throughout the world. You can look up the Standard UTC Offset for your locations using the link to the wikipedia article included in the spreadsheet. In other words, 'Standard' time refers to when the location is NOT on Daylight Saving Time. The 'Standard' UTC Offset is the offset for the location in mid-winter. You could enter a person's name if you wanted to. The labels are just labels, so it doesn't matter what you call each location. Then, every time the spreadsheet recalculates, such as after press F9, the dates and clocks will update to show the current time. Therefore, there are more than the theoretic 24 time zones around the world.Enter the formula =TODAY() in the start date field and =NOW()-TODAY() in the start time field. Additionally, several time zones are 30 and 45 minutes apart. The International Date Line adds 3 to the total of time zones around the world. Heading west of the Prime Meridian / Greenwich Meridian, time is earlier while heading in an easterly direction time is later. Most time zones are exactly one hour apart and their time is calculated as an offset from Coordinated Universal Time you can see this in our time zone map or by using our time zone converter to check the time difference between one location and another. Calculations can also be done using local time once the expected time difference is known. The fact that time zones around the world are all calculated as an offset or difference from standard time makes it easy to know the time of a place by just knowing the time zone it falls in and the standard time at the current moment. Every place on Earth is measured either in degrees east or degrees west of this line. The Meridian, after which GMT is named, is used to represent 0 degrees longitude (although it is not truly 0 degrees). In 1847, the British railroads accepted GMT as a standard. GMT was the same as Universal Time up until 1972. To calculate the time zone an area theoretically falls in, the measurement of the area’s longitudinal coordinate is divided by 15. This means that, in the spring, a clock will go from 4:00 Standard Time to 5:00 DST.

World Clocks are adjusted forward by one hour in the early spring and then set back by one hour in the autumn. Therefore, for half of the year some countries adjust their clocks by one hour. For instance, Saudi Arabia, which is 3 hours ahead of the UK, has a time zone of “GMT +3” and Colombia, which is 5 hours behind the UK, has a time zone of “GMT -5”.ĭaylight Savings Time (DST) is practiced in certain parts of the world in order to allow for more hours of daylight during the working day. The UK sets the standard for Greenwich Mean Time at “ GMT 0” and other countries can calculate their time zone in accordance with how many hours they are ahead of or behind the UK. There are 24 different time zones on earth to correlate with the 24 hours in each day and which are displayed in our time zone map here at World Clock. Time zones are regions of the earth divided by lines of longitude. However, there is no actual time difference between GMT and UTC and therefore the two can be used interchangeably.

There are two standards by which a country’s time zone is categorized the older of the two standards is Greenwich Mean Time (GMT) and the more modern of the two standards is Coordinated Universal Time ( UTC). Whether you’re looking to book a flight, schedule an international teleconference, use our time zone converter or our time zone map and observe the trading hours of an overseas business, can show you the time in a matter of seconds. With incomparable time-telling precision, World Clock is the perfect point of reference for travelers and business people alike. provides accurate world time, statistics and weather in major cities across the world.

Global time zone meeting planner