The Islamic calendar, known as the Hijri calendar, is a purely lunar calendar of twelve months totaling 354 or 355 days. Each month begins with the sighting of the new crescent moon (hilal), and ends when the next crescent is sighted. Because the lunar year is roughly 10 to 11 days shorter than the Gregorian solar year, Islamic dates shift through all seasons over a cycle of approximately 33 years. There is no leap month and no fixed astronomical anchor to a solar event; the calendar is defined entirely by the cycles of the moon.

The calendar takes its name from the Hijra – the migration of the Prophet Muhammad (peace be upon him) and his Companions from Makkah to Madinah in 622 CE. The Caliph Umar ibn al-Khattab (may Allah be pleased with him) established the Hijri calendar approximately seventeen years after the migration, choosing the year of the Hijra rather than the year of the Prophet’s birth or the first revelation as its starting point. Year 1 AH (Anno Hegirae) therefore begins with 1 Muharram of the year of the migration.

The Qur’anic foundation for the twelve-month calendar is stated directly in Surah at-Tawbah 9:36: “Indeed, the number of months with Allah is twelve [lunar] months in the register of Allah [from] the day He created the heavens and the earth; of these, four are sacred.” This verse fixes the count at twelve, ties that count to the original creation, and designates four of those months as sacred – a structure that pre-dates Islam and was reaffirmed by the Qur’an.

The twelve months in order are: Muharram, Safar, Rabi al-Awwal, Rabi al-Thani, Jumada al-Ula, Jumada al-Akhira, Rajab, Sha’ban, Ramadan, Shawwal, Dhul-Qi’dah, and Dhul-Hijjah. Several carry deep ritual significance: Ramadan is the month of obligatory fasting; Dhul-Hijjah contains Hajj, the Day of Arafah, and Eid al-Adha; Muharram contains the Day of Ashura; and Rajab is one of the four sacred months. The names themselves are pre-Islamic Arabic and were preserved unchanged by the Qur’an.

Because the calendar follows actual lunar observation rather than a fixed calculation, the official start of each month can differ by a day or two between regions. Most Muslim communities accept either local sighting or the announcement of a recognized authority, while some rely on astronomical calculation. The dates shown on the Parallel Qur’an calendar are calculated approximations; for ritual observances such as Ramadan, Eid al-Fitr, and the days of Hajj, the authoritative date is the one announced after the actual moon sighting in your community.