Calendar Systems

The Gregorian calendar is the civil calendar of nearly the whole world. Introduced by Pope Gregory XIII in 1582, it keeps the...

Julius Caesar's calendar, designed mainly by the astronomer Sosigenes of Alexandria, took effect on 1 January 45 BCE. It has...

Proposed by the Serbian scientist Milutin Milanković and considered at a pan-Orthodox congress in Constantinople in May and June...

The Hebrew calendar has months of 29 or 30 days tied to the Moon and adds a thirteenth month, Adar I, in years 3, 6, 8, 11, 14...

The Hijri calendar is purely lunar, with 12 months of 29 or 30 days and no intercalation, so it moves through the seasons in a...

The Solar Hijri calendar, official in Iran and also used in Afghanistan, counts years from the Hijra of 622 but follows the Sun...

The traditional Chinese calendar has months that begin at the new moon and inserts a leap month roughly every three years so that...

The Hindu calendars, known as panchanga, combine lunar months with sidereal solar reckoning and insert an extra month, adhika...

India's official civil calendar, also called the Saka calendar, was adopted on 22 March 1957, which became 1 Chaitra 1879 Saka...

Ethiopia's official calendar has twelve months of 30 days plus Pagume, a thirteenth month of five or six days. Its leap year...

The Coptic calendar, used by the Coptic Orthodox Church and by Egyptian farmers, descends from the ancient Egyptian civil...

Revolutionary France replaced the Gregorian calendar with twelve months of 30 days, each split into three ten-day décades, plus...

The Long Count is a running tally of days in units of k'in (1 day), winal (20), tun (360), k'atun (7200) and b'ak'tun (144,000...

The Tzolk'in is the 260-day ritual calendar of the Maya, combining the numbers 1 to 13 with 20 named days. It ran alongside the...

The Aztecs used a 365-day year, the xiuhpohualli, of 18 periods of 20 days plus five nemontemi days, and a 260-day ritual count...

The Egyptian civil calendar had three seasons, Akhet, Peret and Shemu, each of four 30-day months, plus five epagomenal days...

Before Caesar's reform the Roman year normally had 355 days, kept in step with the seasons by an intercalary month, Mercedonius...

The Babylonian calendar began each month at the first sighting of the crescent moon and its year in spring with the month...

The Badí' calendar of the Bahá'í Faith, created by the Báb and adopted by Bahá'u'lláh, has 19 months of 19 days plus four or five...

King Chulalongkorn adopted a Gregorian-based solar calendar for Siam in 1888. Years were first counted in the Rattanakosin Era...

Zoroastrian calendars have twelve months of 30 days, each day dedicated to a divinity, plus five Gatha days. Disputes over...

The agrarian calendar of the Amazigh peoples of North Africa follows the Julian calendar, so its new year, Yennayer, falls around...

The Tibetan calendar is lunisolar and based on the Kalachakra Tantra, with an intercalary month added as needed and some calendar...

The Pawukon of Bali is a 210-day cycle of 30 named weeks, wuku, of seven days. Running concurrently with it are weeks of every...

The Bengali calendar, or Bangabda, is a solar calendar whose new year, Pohela Boishakh, is a major festival in Bangladesh and...

The Nanakshahi calendar was designed by Pal Singh Purewal to fix Sikh festivals to a tropical solar year, with year one in 1469...

Moses Cotsworth proposed a perpetual calendar of 13 months of exactly 28 days, with a new month, Sol, between June and July and...

Elisabeth Achelis promoted the World Calendar from 1930: four identical quarters of 91 days with months of 31, 30 and 30 days...

The ISO week date in ISO 8601, first published in 1988, numbers weeks from Monday to Sunday. Week 1 is the week containing the...

North Korea counts years from the 1912 birth of Kim Il Sung, alongside the Gregorian calendar, under a system adopted on the...

The Akan people of Ghana and Ivory Coast combine a six day week with the seven day week, producing named sacred days that recur...