This is a list of calendars. Included are historical calendars as well as proposed ones. Historical calendars are often grouped into larger categories by cultural sphere or historical period; thus O'Neil (1976) distinguishes the groupings Egyptian calendars (Ancient Egypt),

Babylonian calendar The Babylonian calendar was a lunisolar calendar with years consisting of 12 lunar months, each beginning when a new crescent moon was first sighted low on the western horizon at sunset, plus an intercalary month inserted as needed by decree. Th ...

s (Ancient Mesopotamia), Indian calendars (Hindu and Buddhist traditions of the Indian subcontinent), Chinese calendars and

Mesoamerican calendar Mesoamerican calendars are the calendrical systems devised and used by the pre-Columbian cultures of Mesoamerica. Besides keeping time, Mesoamerican calendars were also used in religious observances and social rituals, such as for divination. ...

s. These are not specific calendars but series of historical calendars undergoing reforms or regional diversification. In

Classical Antiquity Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the interlocking civilizations of ...

, the Hellenic calendars inspired the

Roman calendar The Roman calendar was the calendar used by the Roman Kingdom and Roman Republic. The term often includes the Julian calendar established by the reforms of the dictator Julius Caesar and emperor Augustus in the late 1stcenturyBC and sometim ...

, including the solar

Julian calendar The Julian calendar, proposed by Roman consul Julius Caesar in 46 BC, was a reform of the Roman calendar. It took effect on , by edict. It was designed with the aid of Greek mathematicians and astronomers such as Sosigenes of Alexandr ...

introduced in 45 BC. Many modern calendar proposals, including the

Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years dif ...

introduced in 1582 AD, contains modifications from that of the Julian calendar.

List of calendars

In the list below, specific calendars are given, listed by calendar type (solar, lunisolar or lunar), time of introduction (if known), and the context of use and cultural or historical grouping (if applicable). Where appropriate, the regional or historical group (

Jewish calendar The Hebrew calendar ( he, הַלּוּחַ הָעִבְרִי, translit=HaLuah HaIvri), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance, and as an official calendar of the state of Israel. ...

Hijri calendar The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ, translit=al-taqwīm al-hijrī), also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 or ...

, Mayan, Aztecan, Egyptian, Mesopotamian,

Iranian Iranian may refer to: * Iran, a sovereign state * Iranian peoples, the speakers of the Iranian languages. The term Iranic peoples is also used for this term to distinguish the pan ethnic term from Iranian, used for the people of Iran * Iranian lan ...

Hindu Hindus (; ) are people who religiously adhere to Hinduism. Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...

Buddhist Buddhism ( , ), also known as Buddha Dharma and Dharmavinaya (), is an Indian religion or philosophical tradition based on teachings attributed to the Buddha. It originated in northern India as a -movement in the 5th century BCE, and ...

, Pre-Columbian Mesoamerican, Hellenic, Julian or Gregorian-derived) is noted. Calendars fall into four types:

lunisolar A lunisolar calendar is a calendar in many cultures, combining lunar calendars and solar calendars. The date of Lunisolar calendars therefore indicates both the Moon phase and the time of the solar year, that is the position of the Sun in the E ...

, solar, lunar and seasonal. Most pre-modern calendars are lunisolar. The seasonal calendars rely on changes in the environment (e.g., "wet season", "dry season") rather than lunar or solar observations. The Islamic and some Buddhist calendars are lunar, while most modern calendars are solar, based on either the Julian or the Gregorian calendars. Some calendars listed are identical to the Gregorian calendar except for substituting regional month names or using a different calendar epoch. For example, the

Thai solar calendar The Thai solar calendar ( th, ปฏิทินสุริยคติ, , "solar calendar") was adopted by King Chulalongkorn (Rama V) in 1888 CE as the Siamese version of the Gregorian calendar, replacing the Thai lunar calendar as the lega ...

(introduced 1888) is the Gregorian calendar using a different epoch (543 BC) and different names for the Gregorian months (Thai names based on the signs of the zodiac).

Variant month names

Regional or historical names for lunations or Julian/Gregorian months

Non-standard weeks

Calendaring and timekeeping standards

Coordinated Universal Time Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently use ...

, adopted 1960 and since 1972 including a system of observation-based

leap second A leap second is a one- second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observ ...

s. *

ISO 8601 ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the Geneva-based International Organization for Standardization (ISO) and was first published in 1988, w ...

, standard based on the Gregorian calendar, Coordinated Universal Time and

ISO week date The ISO week date system is effectively a leap week calendar system that is part of the ISO 8601 date and time standard issued by the International Organization for Standardization (ISO) since 1988 (last revised in 2019) and, before that, it was ...

, a leap week calendar system used with the Gregorian calendar *

Fiscal year A fiscal year (or financial year, or sometimes budget year) is used in government accounting, which varies between countries, and for budget purposes. It is also used for financial reporting by businesses and other organizations. Laws in many ...

varies with different countries. Used in accounting only. *

360-day calendar The 360-day calendar is a method of measuring durations used in financial markets, in computer models, in ancient literature, and in prophetic literary genres. It is based on merging the three major calendar systems into one complex clock, with ...

used for accounting *

365-day calendar A 365-day calendar consists of exactly 365 days per year (in common years), and is primarily used in computer models and as an assumption in every-day calculations. For example, a calculation of a daily rate may use an annual total divided by exact ...

used for accounting *

Unix time Current Unix time () Unix time is a date and time representation widely used in computing. It measures time by the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970, the beginning of the Unix epoch, less adjustments m ...

, number of seconds elapsed since 1 January 1970, 00:00:00 (UTC). * Julian day, number of days elapsed since 1 January 4713 BC, 12:00:00 (UTC). * Heliocentric Julian Date, Julian day corrected for differences in the Earth's position with respect to the Sun. * Barycentric Julian Date, Julian day corrected for differences in the Earth's position with respect to the barycentre of the Solar System. * Lilian date, number of days elapsed since the beginning of the Gregorian Calendar on 15 October 1582. * Rata Die, number of days elapsed since 1 January 1 AD 1 in the proleptic

Non-Earth or fictional

* Darian calendar (proposed for Mars, not used in planetary science) * Discworld calendar (fictional) * Middle-earth calendars (fictional) * Stardates (from Star Trek, fictional)

References

*Brian Williams, ''Calendars'', Cherrytree Books, 2002. *Sacha Stern, ''Calendars in Antiquity: Empires, States, and Societies'', OUP Oxford, 2012. *William Matthew O'Neil, ''Time and the Calendars'', Manchester University Press, 1976. *Anthony F. Aveni, ''Empires of Time: Calendars, Clocks and Cultures'', Tauris Parke Paperbacks, 2000. {{calendars List