Eid al-Adha begins on the 10th day of Dhu al-Hijjah, the final month of the Islamic calendar.
The date connects the festival with the Hajj pilgrimage. Pilgrims gather on the plain of Arafat on the 9th of Dhu al-Hijjah, and Eid follows the next day. Muslims mark the occasion with a special prayer, charity, and the sacrifice known as udhiyah or qurbani.
The celebration commonly lasts four days, from the 10th through the 13th of Dhu al-Hijjah. The three days after Eid are called the Tashreeq days, during which pilgrims continue important Hajj rituals.
A common mix-up is confusing Eid al-Adha with Eid al-Fitr, which occurs on the first day of Shawwal after Ramadan. Because the Islamic calendar is lunar, Eid al-Adha moves through the Gregorian calendar each year, and its local date can differ depending on moon-sighting practices.