The date of Hajj is determined by the Islamic calendar (known as Hijri calendar or AH), which is based on the lunar year.Every year, the events of Hajj take place in a five-day period, starting on 8 and ending on 12 Dhu al-Hijjah, the twelfth and last month of the Islamic calendar. Among these five days, the 9th Dhul-Hijjah is known as Day of Arafah, and this day is called the day of Hajj. Because the Islamic calendar is lunar and the Islamic year is about eleven days shorter than the Gregorian year, the Gregorian date for Hajj changes from year to year. Thus, each year in the Gregorian calendar, the pilgrimage starts eleven days (sometimes ten days) earlier than the preceding year.This makes it possible for the Hajj season to fall twice in one Gregorian year, and it does so every 33 years.
The date of the Hajj is 31 August 2017 (Day of Arafat).