What Is the Islamic Hijri Calendar?

The Hijri calendar — also called the Islamic lunar calendar — is the official timekeeping system used by Muslims around the world to determine the dates of religious observances and events. Unlike the Gregorian calendar, which is based on the solar year, the Hijri calendar tracks time by the phases of the moon.

The Origin of the Hijri Calendar

The calendar traces its beginning to 622 CE, the year the Prophet Muhammad ﷺ migrated from Mecca to Medina — an event known as the Hijra. In 638 CE, Caliph Umar ibn al-Khattab established a formal Islamic calendar starting from this momentous migration. The companions agreed that Muharram would be the first month, as it follows the Hajj season, and the year of the Hijra became Year 1 AH (Anno Hegirae).

The Twelve Months of the Hijri Calendar

1. Muharram – The first and one of four sacred months; features the Day of Ashura on the 10th.
2. Safar – The second month, with no special religious significance.
3. Rabi al-Awwal – The month of the Prophet's birth and passing.
4. Rabi al-Thani – The fourth month of the year.
5. Jumada al-Ula – The fifth month.
6. Jumada al-Akhira – The sixth month.
7. Rajab – A sacred month; the Night of Isra and Miraj occurs here.
8. Shaban – The month before Ramadan; the Prophet ﷺ fasted often in it.
9. Ramadan – The holiest month; month of fasting and the revelation of the Quran.
10. Shawwal – Begins with Eid al-Fitr.
11. Dhul Qidah – A sacred month preceding Hajj season.
12. Dhul Hijjah – The month of Hajj and Eid al-Adha.

How Is the Start of Each Month Determined?

Traditionally, each new month begins with the naked-eye sighting of the crescent moon after sunset on the 29th day. If the crescent is seen, the new month begins with 29 days in the old month. If not, the month is completed to 30 days. In modern times, many countries use astronomical calculation to predict month beginnings in advance.

Why Does Ramadan Shift Each Year?

A Hijri year has 354 or 355 days compared to 365 or 366 in the Gregorian year — a difference of about 11 days. This means Islamic observances advance roughly 11 days each year through the Gregorian calendar. Over a cycle of approximately 33 Gregorian years, Ramadan moves through all four seasons.

Why the Hijri Calendar Matters

The Hijri calendar governs the timing of all major Islamic pillars: fasting in Ramadan, performing Hajj in Dhul Hijjah, paying Zakat al-Fitr, and celebrating Eid. It is also used in Islamic jurisprudence to calculate waiting periods, nursing periods, and other time-sensitive rulings.