text: The present Iranian calendar was legally adopted on 31 March 1925, under the early Pahlavi dynasty. The law said that the first day of the year should be the first day of spring in "the true solar year", "as it has been" ever so. It also fixed the number of days in each month, which previously varied by year with the sidereal zodiac. It revived the ancient Persian names, which are still used. 1 Farvardin is the day whose midnight start is nearest to the instant of vernal equinox. The first six months have 31 days, the next five thirty, and the twelfth has 29 days and 30 in leap years.
  It specified the origin of the calendar to be the Hijrah of Muhammad from Mecca to Medina in AD 622. It also deprecated the 12-year cycles of the Chinese-Uighur calendar which were not officially sanctioned but were commonly used.
  In 1976, Shah Mohammad Reza Pahlavi changed the origin of the calendar to the beginning of Cyrus the Great's reign as its first year, rather than the Hijra of Muhammad. Overnight, the year changed from 1355 to 2535. This change only lasted until the Iranian revolution in 1979, at which time the calendar reverted to Solar Hijri.
  Correspondence of Solar Hijri and Gregorian calendars (Solar Hijri leap years are marked *):