Zoroastrian calendar

This article treats the reckoning of days, months and years in the calendar used by adherents of the Zoroastrian faith. Zoroastrian religious festivals are discussed elsewhere, but have a fixed relationship to Nawruz, the New Year festival, whose timing is discussed below. Three distinct versions of the calendar are currently in use by different Zoroastrian communities.

In this article, except where explicitly noted to the contrary, Western-style dates prior to October 5, AD 1582 are reckoned according to the Julian calendar; subsequent dates are according to the Gregorian calendar, in which 15 October 1582 (Gregorian) was the day following 4 October 1582 (Julian).

English spellings follow this recommended usage.

The forerunner of all modern Zoroastrian calendars is the system used to reckon dates in the Persian Empire. In 539 BC, Persia's rulers conquered Babylon, and soon afterwards – at least by the 4th century BC – adopted the Babylonian luni-solar calendar for civil purposes. This kept in step with the seasons, unlike the religious calendar which consisted of 12 months each containing 30 days, adjusted at that time by the addition of five epagomenal days at the end of the year to bring the total up to 365. The earliest Zoroastrian calendar (also misleadingly called "Avestan calendar" although it is younger than the Avesta proper) follows the Babylonian in relating the seventh and other days of the month to Ahura Mazda.

This "Avestan calendar" of 360 days required regular correction to keep it synchronised with the solar year; this was achieved by intercalating a 13th month roughly once every six years.

In the civil calendar, intercalations did not always follow a regular pattern, but during the reign of Artaxerxes II (circa 380 BC) astronomers utilised a 19-year cycle which required the addition of a month called Addaru II in years 3, 6, 8, 11, 14 and 19, and the month Ululu II in year 17 of the cycle. Older research suggests the first intercalation took place in 309 BC. Fuller information on the naming of months in the Zoroastrian calendar will be found below, but it should be noted that the first month of the year was called Frawardin, and the first day of Frawardin was the 'New Year's Day' or Nawruz (also reckoned Now-Ruz, Nowruz, No Roz, No-Rooz, Norouz, or Navroz), from which all other religious observances were reckoned – this day being, in theory, the day of the northern vernal equinox, 21 March (Gregorian).

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