Understanding the world’s time zone can be challenging even for a frequent traveler. You may be a pro traveler, but you’ve most likely experienced jet lag and travel fatigue when traveling across the country or around the world. You’ve had to adjust your watch when you crossed the Atlantic Ocean or flew from the East Coast to the West Coast. And you’ve most certainly tried to figure out how to make up for the lost time when you traveled eastwards or felt happy over “gaining time” when you arrived at a westward location in an earlier time zone as your home city.
For international travelers, one of the first things you wonder about when planning a trip to a faraway destination is the time zone, what time it is at that location, and perhaps the weather as well, and somehow, it seems like every country is on a different time than where you live. For instance, when it’s 7 pm in Portofino, Italy, it’s noon in Chicago, and even more confusing, it’s 10 am in Seattle – all on the same day! And when you factor in Daylight Saving Time (DST), it can add more confusion because some places like Santa Barbara, California, which are typically on a Pacific Standard Time (PST), revert to using Pacific Daylight Time (PDT) during certain times of the year, while most cities in Arizona do not observe DST.
Remembering all the different time zones in the world may be difficult, but understanding the basics of how time zones work and why they exist can help us plan for better travel, adapt to time zone change, and manage jet lag symptoms when traveling outside our home time zone.
What are Time Zones
A time zone refers to the local time of a region, area, or country. Every region of the world belongs to a specific time zone, and within that time zone, a uniform standard time is maintained. This uniform standard time, or local time within a time zone, is based on the concept of Coordinated Universal Time (UTC) which is the world’s time standard.
What is UTC
UTC or Coordinated Universal Time (UTC) is a point of reference for which other times are extrapolated. It is based on the prime meridian, which is the starting point for measuring the distance around the earth – east and west. In 1884, after years of confusion across nations on how to measure the distance around the world, the prime meridian (the main point of reference) was arbitrarily assigned to a longitude (meridian) that passed through the Royal Observatory in Greenwich, England, and designated as 0° longitude or Greenwich Meridian. It is still the standard for longitude. If you ever travel to Greenwich, you can actually stand on both sides of the line and straddle both the eastern and western hemispheres.
UTC is determined by the International Atomic Time (TAI) and the Universal Time (UT). TAI is a time scale that provides the exact speed our click should tick based on the speed of four hundred atomic clocks around the world. UT, also known as a solar time or astronomical time, is determined by the rotation of the earth. TAI and UT work hand-in-hand and as double-checks for each other. All time zones around the world are expressed as positive or negatives factors of UTC. It is also the standard time used in the aviation industry to avoid confusion. UTC is permanent and never changes for daylight savings; however, the designation of UTC in relation to a region can vary. For example, New York City is UTC-5:00 hours (which we know as Eastern Time Zone). This means that UTC is five hours ahead of New York City. During daylight savings time, NYC becomes UTC-4:00 hours, which simply means UTC is four hours ahead of New York City. Portland, Oregon, which we know as Pacific Standard Time (PST), is UTC-8:00 hours, which makes it eight hours behind UTC.
The original world time standard, Greenwich Mean Time (GMT) was also based on the prime meridian, and UTC is the successor for GMT. For years, Greenwich Mean Time (GMT) was used as the world’s standard time; however, in 1960, the International Radio Consultative Committee conceptualized UTC and formalized it in 1967. GMT is now just a time zone like Eastern Standard Time (EST) or Pacific Standard Time and is used in Britain, Iceland, and some countries in Africa and Western Europe.
How Do Time Zones Work
Time zones were originally based on the longitude of a destination; however, due to commercial, communication, legal, and political interests, time zones are currently based on the boundaries of countries as well as their subdivisions. Most time zones are whole number offsets from the UTC (example UTC-8:00, UTC +6:00), but a few others are offsets by thirty minutes, like IST (Indian Standard Time – example UTC+5:30), and forty-five minutes (UTC+5:45) like Nepal Standard Time.
With all this information, it is easy to get very confused about how time zones work and why they even exist. Since Earth is round and rotates completely every twenty-four hours, not everyone can be on the same exact time. If we were, some places of the world would be completely dark during their daytime hours and bright and sunny at night all the time. If the earth rotates 360 degrees in twenty-four hours, that means it moves just about 15 degrees every hour. With this information, the earth was sectioned in twenty-four parts with each 15-degree rotation equating to an hour difference in time. Over time, and due to logistical and political reasons, time zones followed the countries’ boundaries rather than just the earth’s rotations.
The International Dateline
Another component of time zones is the International Dateline (IDL). This is an imaginary line that runs from the North Pole to the South Pole passing through the middle of the Pacific Ocean and roughly tracing the 180° latitude line of the earth. It is about halfway around the world from the Greenwich Meridian and separates two consecutive calendar days. When traveling westward, travelers must set their clocks forward by twenty-four hours when they cross the IDL to sync with the local time. Conversely, travelers traveling eastwards must “fall back” by twenty-four hours once they cross the IDL.
How Many Times Zones Are There In The World
There are currently about 38 time zones in use. If time zone were based on one time zone per hour, we would have had twenty-four time zones only, but since some regions are offset by just thirty or forty-five minutes, that adds more time zones to the mix. And when we factor in daylight savings time (DST), we get more local time differences. Some countries, like India and China, even though geographically wide, base their time zone on their international boundaries and use one time zone for the entire country, whereas the United States, which is also a wide country, uses different time zones internally.
USA Time Zones
Most of us are familiar with the four-time zones used within the contiguous USA (48 states and District of Columbia), but the United States observes six main time zones with the other two located in Alaska and Hawaii.
• Pacific Standard Time
• Mountain Standard Time
• Central Standard Time
• Eastern Standard Time
• Hawaii-Aleutian Standard Time/Hawaii Standard Time)
• Alaska Standard Time
Due to the width of the country, some states fall in more than just one-time zone. Currently, thirteen states, including Indiana, Oregon, Kentucky, Idaho, Texas, Nebraska, Kansas, Florida, North Dakota, South Dakota, Michigan, Tennessee, and Alaska have more than one-time zone.
Daylight Saving Time (DST) is observed by all states except in Hawaii and most of Arizona and starts on the second Sunday of March, lasting through the first Sunday of November. During daylight savings, the clock is set forward by an hour and reversed when daylight savings ends. All the time zones (except Hawaii Standard Time) have corresponding DST zones, so Pacific Standard Time turns into Pacific Daylight Time during the daylight savings period.
Apart from these six main time zones, the USA has three other time zones based on the time zones in the five US permanently inhibited territories – Puerto Rico, U.S. Virgin Islands, American Samoa, Guam, and the Northern Mariana Islands. The Atlantic Standard Time Zone (UTC-4) is used in Puerto Rico and U.S. Virgin Islands; the Samoa Standard Time (UTC-11) is used in America Samoa; and, the Chamorro Standard Time (UTC+10) is used in Guam and the Northern Mariana Islands.
When you are planning a trip, make sure to check the local times, especially if you’re heading to an exciting USA destination not typically on your radar. Knowing the time differences between your state and a destination state can help you plan your activities better, as well as help you manage jetlag.
Canada Time Zones
There are six time zones in Canada, with corresponding daylight saving times (DST) adjusted by adding one hour to the clock, spanning over four-and-half hour time differences. Although Daylight Savings Time is officially observed from March to November, some parts of the country, like Yukon, Southampton Island, and parts of Saskatchewan, parts of Quebec, and parts of British Columbia do not adjust their time during Daylight Savings. The six main time zones include:
• Pacific Standard Time UTC-8:00 (with corresponding DST)
• Mountain Standard Time UTC-7:00 (with corresponding DST)
• Central Standard Time UTC-6:00 (with corresponding DST)
• Eastern Standard Time UTC-5:00 (with corresponding DST)
• Atlantic Standard Time UTC-4:00 (with corresponding DST)
• Newfoundland Standard Time UTC-3:30 (with corresponding DST)
Mexico Time Zones
If you’ve traveled to different parts of Mexico, you might have noticed how variable the time zones can be depending on what time of the year and what location you travel to. At first, Mexico was divided into two time zones, but by February 2015, Mexico had four standard time zones similar to time zones in the contiguous US.
• Zona Sureste (Southwest Zone) similar to US Eastern Standard Time
• Zona Centro (Central Zone) similar to US Central Time
• Zona Pacifico (Pacific Zone) similar to US Mountain Time
• Zona Noroeste (Northwest Zone) similar to US Pacific Time
In observance of seasonal changes, some parts of Mexico observe three daylight saving times (DST) – Mountain Daylight Time, Central Daylight Time, and Pacific Daylight Time. The official daylight saving period is from the first Sunday of April through the last Sunday of October; however, clock-times are not changed on the same date across all Mexican time zones, leading to disparity in the time for weeks during the Fall and Spring. Some Mexican states, especially those along the US-Mexico border, sync their clock with the nearest US cities rather than the Mexico time zone where they are geographically located.
Europe Time Zones
Europe generally spans from Iceland to the western part of Russia, and this entire landmass has seven main time zones in Europe (excluding the daylight-saving times) spanning from UTC -1:00 to UTC+5:00. Daylight Savings Time (DST) is coordinated, observed across four time zones, and starts from the last Sunday of March through the last Sunday of October. The furthest time zone on the west, Further Western European Time UTC-1 (with corresponding DST) is observed in the Azores while Further Eastern Time is observed in countries like Turkey, most of western Russia, and Belarus.
Three other time zones – Western European Time, Central European Time, and Eastern Time, all with corresponding DST, are observed in most parts of Europe. Other time zones observed in Europe include Armenia Time/Georgia Time/Azerbaijan/Samara Time, all at UTC+4:00, and West Kazakhstan Time/Yekaterinburg Time, both at UTC+5:00.
There are a few exceptions to the general time zones, including Russia, a transcontinental country spread between Eastern Europe and Northern Asia, which is also the largest country in the world. Due to its massive landmass and width, Russia has eleven time zones spanning from UTC+2:00 to UTC+12:00.
Though the time differences in western, central, and eastern Europe might not be significant, it is still a good idea to check the time difference between home and your destination European city. For instance, Monaco is UTC+1:00 while The United Kingdom is UTC, so knowing that there is an hour difference between both countries can help you plan your travel activities better, especially if you plan to move from one European destination to another.
Africa Time Zones
There are currently six major time zones in Africa; however, these time zones are represented by thirteen different names. Going from the westernmost part of Africa to the Easternmost part of Africa, the time zones are offsets of UTC and include:
• Cape Verde Time Zone – UTC-1:00
• Greenwich Mean Time– UTC+0
• West Africa Time – UTC+1:00
• Central Africa Time and South African Standard Time Zones – UTC+2:00
• East Africa Time – UTC+3:00
• Mauritius, Reunion, and Seychelles Time Zone – UTC +4:00
Most African countries do not change the clock for daylight savings, except Morocco, which observes a permanent daylight savings time year-round, excluding Ramadan.
Australia Time Zones
Australia might be the sixth-largest country by population in the world, about the size of the continental USA, and the only continent that’s also a country, but it is only divided into three different official time zones. Those time zones include:
• Australian Eastern Standard Time (AEST) at UTC +10:00
• Australian Central Standard Time (ACST) at UTC +9:30
• Australian Western Standard Time (AWST) at UTC+ 8:00
Except for Queensland, Western Australia, and the Northern Territory, the rest of Australia observes Daylight Savings Time (DST) starting from the first Sunday of October through the first Sunday in April. The DST corresponds to the eastern and central areas that turn their clocks one hour forward – Australian Eastern Daylight Time and Australian Central Daylight Time. Apart from the physical distance, you might travel when going to Australia from North America, for example, California to Sydney, you do cross the International Date Line when crossing the Pacific Ocean, essentially changing the date by one day.
There is also a hybrid time zone known as the Australian Central Western Standard Time (ACWST) UTC+8:45, and visitors to this part of Australia are reminded with a highway sign to advance their clock by forty-five minutes! Since Australia has some dependencies, the time zones used in these countries vary slightly from those used in mainland Australia, so you will also see Christmas Island Standard (UTC +7:00), and Cocos Island Standard (UTC +6:30) as time zones listed for Australia.
Asia Time Zones
Asia is the largest continent in the world with about sixty percent of the world’s population spread over forty countries within Asia. The number of time zones – eleven different time zones observed within the continent reflect the expanse of the land. Asia observes eleven different time zones spanning from UTC+4:00 to UTC+10:00 with some of the countries ahead of, or behind, other countries of the world by increments of UTC + thirty or forty-five minutes instead of a full hour. With the exception of a few countries like Mongolia, Iran, Israel, Jordan, Lebanon, Syria, and the West Bank, most countries in Asia do not observe Daylight Savings Time either. Even though Asia has eleven official time zones, there is a multitude of abbreviations for the list of time zones within the independent countries, meaning that the same time zone can be abbreviated differently within countries. And if you’ve ever heard of ASEAN Common Time (ACT), it was a proposal for unification of time amongst Association of Southeast Asian Nations member states, but that has failed to pass for many years. For now, since the different time zones make the list of time zones longer than just eleven time zones, it’s best to check the time difference between home and your destination Asian country before your trip. This will help you avoid any surprises as well as be appropriately prepared for jet lag.
China Time Zones
China is the third-largest country in the world and about as wide as the US and given its size, you might expect to see many time zones as we have in the US, which is the fourth largest country. China spans across five time zones and used five different time zones (UTC+5:30, UTC+6:00, UTC+7:00, UTC+8:00, and UTC+8:30) for telling time until the end of the Chinese Civil War around 1949-1950 when the government decided to observe one time zone - Beijing Time – internationally known as China Standard Time and set at UTC+8:00. When traveling to China, be prepared to enjoy sunsets and sunrise at seemingly all hours of the day, depending on what part you are visiting. And if you are visiting Xinjiang, which is the westernmost region of China, be sure to ask for local time versus Beijing time as this part of China is an exception to the rule and observes a local time that is closer to solar time and about two hours behind Beijing at UTC+6:00.
Changing time zones can cause jetlag and travel fatigue even in the most prepared and experienced traveler. Time zones are why the clock can read differently at the same exact moment in beautiful Cinque Terre, Italy, and Yellowstone National Park. Knowing that time zones exist based on the degree of rotation of Earth is why you would expect the time to be the same in Caramel-by-the-Sea and Laguna Beach, both within geographical proximity in California. Time zones are important for commercial, communication, and logistical reasons. Time zones are why people from different parts of the world can be on a synchronized conference call at the same time based on an agreed-upon time based on UTC/GMT. Time zone based on Coordinated Universal Time (UTC) is extremely important in international civil aviation for flight departures and arrivals. There may be twenty-four ideal time zones and thirty-eight different local time zones in use around the world, and going from one place to another can pose a challenge when trying to figure out the local time, but knowing how and why time zone works, and where to find the current time where you are, will go a long way to understanding and working with time zones.
Casey Barbles 
Jeff Yelton 