Iranian Calendar

The Iranian year begins on March 21 ending on March 20 in the next Christian year. It is based on the Hejirah solar calendar beginning from the migration of prophet Mohammad (SAWA) from Mecca to Medina in 621-622 A.D.The solar year consists of the duration of one full orbit of the Earth around the Sun. the lunar Hejirah year based on which religious feasts and rituals are observed, On the other hand consists of the duration of one full orbit of the Moon around the Earth. Owing to this difference the days in the lunar and solar calendars do not overlap and there are 32 solar years in every 33 lunar years. A solar year consists of 365 days while there are only 354 days in every lunar year.
Furthermore, the new moon is seen in Arab countries one day earlier, thus there is a difference of one day in important religious days in Iran and the Arab states.
The months on the solar calendar are:

  Farvardin March 21-April 20
Spring Ordibehesht April 21-May 21
  Khordad May 22-June 21
  Tir June 22-July 22
Summer Mordad=Amordad July 23-August 22
  Shahrivar August 23-September 22
  Mehr September 23-October 22
Fall Aban October 23-November 21
  Azar November 22-December 21
  Day December 22-January 20
Winter Bahman January 21-February 19
  Esfand February 20-March 20
 
The first six months of the solar year have 31 days, the next five 30 days and the last one 29 days. However, the month of Esfand will be 30 days in the leap years in which case the year will be 366 days.
The months on the lunar calendar are : Moharram, Safar, Rabi-ol-Aval, Rabi-ol-Thani, Jamadi-ol-Aval, Jamadi-ol-Thani, Rajab, Shaban, Ramazan, Shavval, Zilqada and zilhajja.

To convert lunar and solar years into Christian dates, one may use the following formula:
Lunar year – 41 +*621=Christian year
Solar year + 621*=Christian year
If a date falls between Day 11 and March 20, the figure changes to 622. In the case of lunar years the resulting figure may contain an almost 1/600 error
.