Time zones of the world

A time zone is an area that observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.

All time zones are defined as offsets from Coordinated Universal Time (UTC), ranging from UTC−12:00 to UTC+14:00. The offsets are usually a whole number of hours, but a few zones are offset by an additional 30 or 45 minutes, such as in India, South Australia and Nepal.

Some areas of higher latitude use daylight saving time for about half of the year, typically by adding one hour to local time during spring and summer.

List of UTC offsets

Time zones of the world

In the table below, the locations that use daylight saving time (DST) are listed in their UTC offset when DST is not in effect. When DST is in effect, approximately during spring and summer, their UTC offset is increased by one hour (except for Lord Howe Island, where it is increased by 30 minutes). For example, during the DST period California observes UTC−07:00 and the United Kingdom observes UTC+01:00.

UTC offset	Locations that do not use DST			Locations that use DST
UTC−12:00		Baker Island	Howland Island
UTC−11:00		American Samoa  Jarvis Island  Kingman Reef	Midway Atoll  Niue  Palmyra Atoll
UTC−10:00		Cook Islands  French Polynesia (most)	Johnston Atoll  United States: Hawaii		United States: Andreanof Islands, Islands of Four Mountains, Near Islands, Rat Islands (Aleutian Islands, Alaska)
UTC−09:30		French Polynesia: Marquesas Islands
UTC−09:00		French Polynesia: Gambier Islands			United States: Alaska (most)
UTC−08:00		Clipperton Island  Pitcairn Islands			Canada: British Columbia (most)  Mexico: Baja California	United States: California, Idaho (north), Nevada (most), Oregon (most), Washington
UTC−07:00		Canada: British Columbia (northeast), Yukon  Mexico: Sonora  United States: Arizona (most)			Canada: Alberta, British Columbia (southeast), Northwest Territories, Nunavut (west)  Mexico: Baja California Sur, Chihuahua, Nayarit (most), Sinaloa  United States: Colorado, Idaho (most), Montana, New Mexico, Utah, Wyoming
UTC−06:00		Belize  Canada: Saskatchewan (most)  Costa Rica  Ecuador: Galápagos	El Salvador  Guatemala  Honduras  Nicaragua		Canada: Manitoba, Nunavut (central), Ontario (west)  Chile: Easter Island  Mexico (most)	United States: Alabama, Arkansas, Illinois, Iowa, Kansas (most), Louisiana, Minnesota, Mississippi, Missouri, Nebraska (most), North Dakota (most), Oklahoma, South Dakota (most), Tennessee (most), Texas (most), Wisconsin
UTC−05:00		Brazil: Acre  Canada: Atikokan, Mishkeegogamang, Southampton Island  Cayman Islands  Colombia  Ecuador (most)	Jamaica  Mexico: Quintana Roo  Navassa Island  Panama  Peru		Bahamas  Canada: Nunavut (east), Ontario (most), Quebec (most)  Cuba  Haiti  Turks and Caicos Islands	United States: Connecticut, Delaware, District of Columbia, Florida (most), Georgia, Indiana (most), Kentucky (most), Maine, Maryland, Massachusetts, Michigan (most), New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Vermont, Virginia, West Virginia
UTC−04:00		Anguilla  Antigua and Barbuda  Aruba  Barbados  Bolivia  Brazil: Amazonas (most), Mato Grosso, Mato Grosso do Sul, Rondônia, Roraima  British Virgin Islands  Canada: Quebec (east)  Caribbean Netherlands  Curaçao  Dominica  Dominican Republic  Grenada	Guadeloupe  Guyana  Martinique  Montserrat  Puerto Rico  Saint Barthélemy  Saint Kitts and Nevis  Saint Lucia  Saint Martin  Saint Vincent and the Grenadines  Sint Maarten  Trinidad and Tobago  U.S. Virgin Islands  Venezuela		Bermuda  Canada: Labrador (most), New Brunswick, Nova Scotia, Prince Edward Island  Chile (most)  Greenland: Thule Air Base  Paraguay
UTC−03:30					Canada: Newfoundland, Labrador (southeast)
UTC−03:00		Argentina  Brazil (most)  Chile: Magallanes  Falkland Islands	French Guiana  Suriname  Uruguay		Greenland (most)  Saint Pierre and Miquelon
UTC−02:00		Brazil: Fernando de Noronha  South Georgia and the South Sandwich Islands
UTC−01:00		Cape Verde			Greenland: Ittoqqortoormiit  Portugal: Azores
UTC±00:00		Burkina Faso  Gambia  Ghana  Greenland: Danmarkshavn  Guinea  Guinea-Bissau  Iceland  Ivory Coast	Liberia  Mali  Mauritania  Saint Helena, Ascension and Tristan da Cunha  Senegal  Sierra Leone  São Tomé and Príncipe  Togo		Faroe Islands  Guernsey  Ireland  Isle of Man  Jersey  Portugal (most)  Spain: Canary Islands  United Kingdom
UTC+01:00		Algeria  Angola  Benin  Cameroon  Central African Republic  Chad  Congo  Democratic Republic of the Congo: Équateur, Kinshasa, Kongo Central, Kwango, Kwilu, Mai-Ndombe, Mongala, Nord-Ubangi, Sud-Ubangi, Tshuapa	Equatorial Guinea  Gabon  Morocco[a]  Niger  Nigeria  Tunisia  Western Sahara[a]		Albania  Andorra  Austria  Belgium  Bosnia and Herzegovina  Croatia  Czech Republic  Denmark  France (metropolitan)  Germany  Gibraltar	Hungary  Italy  Kosovo  Liechtenstein  Luxembourg  Malta  Monaco  Montenegro  Netherlands (European)  North Macedonia	Norway  Poland  San Marino  Serbia  Slovakia  Slovenia  Spain (most)  Sweden  Switzerland   Vatican City
UTC+02:00		Botswana  Burundi  Democratic Republic of the Congo (most)  Egypt  Eswatini  Lesotho  Libya  Malawi	Mozambique  Namibia  Russia: Kaliningrad  Rwanda  South Africa (most)  South Sudan  Sudan  Zambia  Zimbabwe		Akrotiri and Dhekelia  Bulgaria  Cyprus  Estonia  Finland  Greece	Israel  Jordan  Latvia  Lebanon  Lithuania  Moldova	Northern Cyprus  Palestine  Romania  Transnistria  Syria  Ukraine (most)
UTC+03:00		Abkhazia  Bahrain  Belarus  Comoros  Djibouti  Eritrea  Ethiopia  French Southern and Antarctic Lands: Scattered Islands[4]  Iraq  Kenya  Kuwait  Madagascar  Mayotte	Qatar  Russia (most of European part)  Saudi Arabia  Somalia  Somaliland  South Africa: Prince Edward Islands  South Ossetia  Tanzania  Turkey  Uganda  Ukraine: occupied territories  Yemen
UTC+03:30					Iran
UTC+04:00		Armenia  Azerbaijan  French Southern and Antarctic Lands: Crozet Islands[4]  Georgia  Mauritius	Oman  Russia: Astrakhan, Samara, Saratov, Udmurtia, Ulyanovsk  Réunion  Seychelles  United Arab Emirates
UTC+04:30		Afghanistan
UTC+05:00		French Southern and Antarctic Lands: Kerguelen Islands, Saint Paul Island, Amsterdam Island  Heard Island and McDonald Islands  Kazakhstan: Aktobe, Atyrau, Baikonur, Kyzylorda, Mangystau, West Kazakhstan  Maldives	Pakistan  Russia: Bashkortostan, Chelyabinsk, Khanty-Mansi, Kurgan, Orenburg, Perm, Sverdlovsk, Tyumen, Yamalia  Tajikistan  Turkmenistan  Uzbekistan
UTC+05:30		India  Sri Lanka
UTC+05:45		Nepal
UTC+06:00		Bangladesh  Bhutan  British Indian Ocean Territory	Kazakhstan (most)  Kyrgyzstan  Russia: Omsk
UTC+06:30		Cocos Islands  Myanmar
UTC+07:00		Cambodia  Christmas Island  Indonesia: Sumatra, Java, West Kalimantan, Central Kalimantan  Laos  Mongolia: Bayan-Ölgii, Khovd, Uvs	Russia: Altai Krai, Altai Republic, Kemerovo, Khakassia, Krasnoyarsk, Novosibirsk, Tomsk, Tuva  Thailand  Vietnam
UTC+08:00		Australia: Western Australia (most)  Brunei  China  Hong Kong  Indonesia: South Kalimantan, East Kalimantan, North Kalimantan, Sulawesi, Bali, West Nusa Tenggara, East Nusa Tenggara	Macau  Malaysia  Mongolia (most)  Philippines  Russia: Buryatia, Irkutsk  Singapore  Taiwan
UTC+08:45		Australia: Eucla
UTC+09:00		East Timor  Indonesia: Maluku, North Maluku, Papua, West Papua  Japan  North Korea	Palau  Russia: Amur, Sakha (most), Zabaykalsky  South Korea
UTC+09:30		Australia: Northern Territory			Australia: South Australia
UTC+10:00		Australia: Queensland  Guam  Micronesia: Chuuk, Yap  Northern Mariana Islands	Papua New Guinea (most)  Russia: Jewish, Khabarovsk, Primorsky, Sakha (central-east)		Australia: Australian Capital Territory, Jervis Bay Territory, New South Wales (most), Tasmania, Victoria
UTC+10:30					Australia: Lord Howe Island
UTC+11:00		Micronesia: Kosrae, Pohnpei  New Caledonia  Papua New Guinea: Bougainville	Russia: Magadan, Sakha (east), Sakhalin  Solomon Islands  Vanuatu		Norfolk Island
UTC+12:00		Fiji  Kiribati: Gilbert Islands  Marshall Islands  Nauru	Russia: Chukotka, Kamchatka  Tuvalu  Wake Island  Wallis and Futuna		New Zealand (most)
UTC+12:45					New Zealand: Chatham Islands
UTC+13:00		Kiribati: Phoenix Islands  Samoa	Tokelau  Tonga
UTC+14:00		Kiribati: Line Islands

History

The apparent position of the Sun in the sky, and thus solar time, varies by location due to the spherical shape of the Earth. This variation corresponds to four minutes of time for every degree of longitude, so for example when it is solar noon in London, it is about 10 minutes before solar noon in Bristol, which is about 2.5 degrees to the west.^[5]

The Royal Observatory, Greenwich, founded in 1675, established Greenwich Mean Time (GMT), the mean solar time at that location, as an aid to mariners to determine longitude at sea, providing a standard reference time while each location in England kept a different time.

Railway time

Plaque commemorating the Railway General Time Convention of 1883 in North America

The control panel of the Time Zone Clock in front of Coventry Transport Museum

In the 19th century, as transportation and telecommunications improved, it became increasingly inconvenient for each location to observe its own solar time. In November 1840, the Great Western Railway started using GMT kept by portable chronometers.^[6] This practice was soon followed by other railway companies in Great Britain and became known as Railway Time.

Around August 23, 1852, time signals were first transmitted by telegraph from the Royal Observatory. By 1855, 98% of Great Britain's public clocks were using GMT, but it was not made the island's legal time until August 2, 1880. Some British clocks from this period have two minute hands, one for the local time and one for GMT.^[7]

On November 2, 1868, the then British Colony of New Zealand officially adopted a standard time to be observed throughout the colony.^[8] It was based on longitude 172°30′ east of Greenwich, that is 11 hours 30 minutes ahead of GMT. This standard was known as New Zealand Mean Time.^[9]

Timekeeping on North American railroads in the 19th century was complex. Each railroad used its own standard time, usually based on the local time of its headquarters or most important terminus, and the railroad's train schedules were published using its own time. Some junctions served by several railroads had a clock for each railroad, each showing a different time.^[10]

1913 time zone map of the United States, showing boundaries very different from today

Charles F. Dowd proposed a system of hourly standard time zones for North American railroads around 1863, although he published nothing on the matter at that time and did not consult railroad officials until 1869. In 1870 he proposed four ideal time zones having north–south borders, the first centered on Washington, D.C., but by 1872 the first was centered on meridian 75° west of Greenwich, with natural borders such as sections of the Appalachian Mountains. Dowd's system was never accepted by North American railroads. Instead, U.S. and Canadian railroads implemented a version proposed by William F. Allen, the editor of the Traveler's Official Railway Guide.^[11] The borders of its time zones ran through railroad stations, often in major cities. For example, the border between its Eastern and Central time zones ran through Detroit, Buffalo, Pittsburgh, Atlanta, and Charleston. It was inaugurated on Sunday, November 18, 1883, also called "The Day of Two Noons",^[12] when each railroad station clock was reset as standard-time noon was reached within each time zone.

The North American zones were named Intercolonial, Eastern, Central, Mountain, and Pacific. Within a year 85% of all cities with populations over 10,000 (about 200 cities) were using standard time.^[13] A notable exception was Detroit (located about halfway between the meridians of Eastern and Central time), which kept local time until 1900, then tried Central Standard Time, local mean time, and Eastern Standard Time (EST) before a May 1915 ordinance settled on EST and was ratified by popular vote in August 1916. The confusion of times came to an end when standard time zones were formally adopted by the U.S. Congress in the Standard Time Act of March 19, 1918.

Worldwide time zones

Italian mathematician Quirico Filopanti introduced the idea of a worldwide system of time zones in his book Miranda!, published in 1858. He proposed 24 hourly time zones, which he called "longitudinal days", the first centred on the meridian of Rome. He also proposed a universal time to be used in astronomy and telegraphy. However, his book attracted no attention until long after his death.^[14][15]

Scottish-born Canadian Sir Sandford Fleming proposed a worldwide system of time zones in 1876 - see Sandford Fleming § Inventor of worldwide standard time. The proposal divided the world into twenty-four time zones labeled A-Y (skipping J), each one covering 15 degrees of longitude. All clocks within each zone would be set to the same time as the others, but differed by one hour from those in the neighboring zones.^[16] He advocated his system at several international conferences, including the International Meridian Conference, where it received some consideration. The system has not been directly adopted, but some maps divide the world into 24 time zones and assign letters to them, similarly to Fleming's system.^[17]

World map of time zones in 1928

By about 1900, almost all inhabited places on Earth had adopted a standard time zone, but only some of them used an hourly offset from GMT. Many applied the time at a local astronomical observatory to an entire country, without any reference to GMT. It took many decades before all time zones were based on some standard offset from GMT or Coordinated Universal Time (UTC). By 1929, the majority of countries had adopted hourly time zones, though some countries such as Iran, India and parts of Australia had time zones with a 30-minute offset. Nepal was the last country to adopt a standard offset, shifting slightly to UTC+05:45 in 1986.^[18]

All nations currently use standard time zones for secular purposes, but not all of them apply the concept as originally conceived. Several countries and subdivisions use half-hour or quarter-hour deviations from standard time. Some countries, such as China and India, use a single time zone even though the extent of their territory far exceeds the ideal 15° of longitude for one hour; other countries, such as Spain and Argentina, use standard hour-based offsets, but not necessarily those that would be determined by their geographical location. The consequences, in some areas, can affect the lives of local citizens, and in extreme cases contribute to larger political issues, such as in the western reaches of China.^[19] In Russia, which has 11 time zones, two time zones were removed in 2010^[20][21] and reinstated in 2014.^[22]

Notation

ISO 8601

ISO 8601 is a standard established by the International Organization for Standardization defining methods of representing dates and times in textual form, including specifications for representing time zones.^[23]

If a time is in Coordinated Universal Time (UTC), a "Z" is added directly after the time without a separating space. "Z" is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "0930Z". Likewise, "14:45:15 UTC" is written as "14:45:15Z" or "144515Z".^[24] UTC time is also known as "Zulu" time, since "Zulu" is a phonetic alphabet code word for the letter "Z".^[24]

Offsets from UTC are written in the format ±hh:mm, ±hhmm, or ±hh (either hours ahead or behind UTC). For example, if the time being described is one hour ahead of UTC (such as the time in Germany during the winter), the zone designator would be "+01:00", "+0100", or simply "+01". This numeric representation of time zones is appended to local times in the same way that alphabetic time zone abbreviations (or "Z", as above) are appended. The offset from UTC changes with daylight saving time, e.g. a time offset in Chicago, which is in the North American Central Time Zone, is "−06:00" for the winter (Central Standard Time) and "−05:00" for the summer (Central Daylight Time).^[25]

Abbreviations

Time zones are often represented by alphabetic abbreviations such as "EST", "WST", and "CST", but these are not part of the international time and date standard ISO 8601. Such designations can be ambiguous; for example, "CST" can mean (North American) Central Standard Time (UTC−06:00), Cuba Standard Time (UTC−05:00) and China Standard Time (UTC+08:00), and it is also a widely used variant of ACST (Australian Central Standard Time, UTC+09:30).^[26]

Conversions

Conversion between time zones obeys the relationship

"time in zone A" − "UTC offset for zone A" = "time in zone B" − "UTC offset for zone B",

in which each side of the equation is equivalent to UTC.

The conversion equation can be rearranged to

"time in zone B" = "time in zone A" − "UTC offset for zone A" + "UTC offset for zone B".

For example, the New York Stock Exchange opens at 09:30 (EST, UTC offset= −05:00). In California (PST, UTC offset= −08:00) and India (IST, UTC offset= +05:30), the New York Stock Exchange opens at

time in California = 09:30 − (−05:00) + (−08:00) = 06:30;

time in India = 09:30 − (−05:00) + (+05:30) = 20:00.

These calculations become more complicated near the time switch to or from daylight saving time, as the UTC offset for the area becomes a function of UTC time.

The time differences may also result in different dates. For example, when it is 22:00 on Monday in Egypt (UTC+02:00), it is 01:00 on Tuesday in Pakistan (UTC+05:00).

The table "Time of day by zone" gives an overview on the time relations between different zones.

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