The Hijri calendar (التقويم الهجري) is the Islamic lunar calendar used to determine the dates of all Islamic events — from Ramadan to Eid, from Hajj to Ashura. Unlike the Gregorian solar calendar (365 days), the Hijri calendar has 12 lunar months totalling approximately 354 days — about 11 days shorter per year. This means Islamic dates shift earlier each year relative to the Gregorian calendar. The calendar began in 622 CE with the Prophet Muhammad's ﷺ migration (Hijra) from Mecca to Medina, making it Year 1 AH (After Hijra).
1) Muharram 2) Safar 3) Rabi al-Awwal 4) Rabi al-Thani 5) Jumada al-Awwal 6) Jumada al-Thani 7) Rajab 8) Sha'ban 9) Ramadan 10) Shawwal 11) Dhul Qa'dah 12) Dhul Hijjah
Allah designated four months as sacred (الأشهر الحرم): Muharram (1st), Rajab (7th), Dhul Qa'dah (11th), and Dhul Hijjah (12th). These are times of increased worship, reflection, and avoiding conflict. Good deeds in these months carry greater reward.
Ramadan (9th month) is the month of fasting when the Quran was revealed. Dhul Hijjah (12th month) is when Hajj takes place and Eid al-Adha is celebrated. The first 10 days of Dhul Hijjah are among the most blessed days of the year.
The Hijri year is about 11 days shorter than the Gregorian year, so Islamic events cycle through all seasons over roughly 33 years. This means Ramadan can fall in summer (long, hot days) or winter (short, easy days) — a mercy that distributes the hardship equally over generations.