The Islamic (Hijri) calendar begins from the Hijrah to Madinah - the migration of Prophet Muhammad (peace be upon him) and his companions from Makkah to Madinah in 622 CE. This event was chosen as the starting point of the Muslim calendar during the caliphate of Umar ibn al-Khattab, who recognised the Hijrah as the most transformative event in Islamic history because it marked the establishment of the first Muslim state and community.
The Hijrah was chosen over other significant events for several reasons. The birth of the Prophet, while important, did not immediately change the political or social order. The conquest of Makkah (630 CE) came much later and represented the culmination of the Islamic mission, not its beginning as an organised community. The first revelation of the Qur'an (610 CE) marked the start of prophethood, but the Muslim community was not yet formed as a political entity.
The Hijri calendar is a purely lunar calendar with 12 months, beginning with Muharram. The year of the Hijrah is designated as 1 AH (After Hijrah).
