The Establishment of the Islamic Hijri Calendar

❧The Arab Calendar Problem

Before the Hijra, the Arabs had no unified calendar. Unlike the Romans and Persians who had developed centralized calendar systems, the Arabs, living in decentralized, tribal Arabia, each had their own informal calendar based on significant local events. Tribes would mark years by saying "the year of the death of so-and-so," or "two years before the Elephant incident." Since these events were local and tribe-specific, no two tribes were counting from the same baseline.

This was compounded by a deeply problematic practice that Allāh Himself addresses in the Qurʾān.

❧The Nasi': Swapping the Sacred Months

Allāh had revealed through the Sharīʿah of Ibrāhīm ʿalayhi al-salām that four months of the lunar year were to be sacred (ḥurum), months during which warfare was forbidden. Allāh says in Sūrat al-Tawbah 9:36:

"Inna ʿiddata al-shuhūri ʿindallāhi ithnā ʿashara shahran fī kitābillāhi yawma khalaqa al-samāwāti wa-l-arḍ, minhā arbaʿatun ḥurum", "The number of months in the sight of Allāh is twelve months in the Book of Allāh, as decreed on the day He created the heavens and the earth. Of them, four are sacred."

These four sacred months are Dhul-Qaʿdah, Dhul-Ḥijjah, Muḥarram, and Rajab. The first three are consecutive; Rajab stands alone.

But the powerful tribes, especially Quraysh, the most powerful of all, would abuse this system through a practice called al-Nasīʾ (النَّسِيء): they would declare that this month was not actually the sacred month but was instead being swapped with another. If they wanted to go to war during Muḥarram, they would simply announce that Muḥarram was now being called Ṣafar, and that Ṣafar was now Muḥarram. Since they had the authority, the other tribes would follow. After decades and centuries of this swapping, the months were entirely jumbled, nobody knew with certainty what the true sequence of the months was.

Allāh says in Sūrat al-Tawbah 9:37: "Innamā al-nasīʾu ziyādatun fī al-kufr", "Verily, the Nasīʾ is an increase in disbelief." Allāh calls this manipulation of the sacred calendar a form of kufr, a rejection of His command.

❧The Prophet's Correction at Hajjat al-Wada'

In the 10th year of the Hijra, the Prophet ﷺ performed his only Hajj: the Ḥajjat al-Wadāʿ (the Farewell Pilgrimage). On that occasion, he announced to the assembled Muslims:

"Rajāʿat ka-yawmi khalaqa Allāhu al-samāwāti wa-l-arḍ", "The months have returned to the order they were on the day Allāh created the heavens and the earth."

This ḥadīth is recorded in Ṣaḥīḥ al-Bukhārī. The Prophet ﷺ was declaring that in this particular year, Allāh had willed that the months had naturally fallen back into their original divinely decreed sequence. And he then announced that this practice of swapping was over. From that moment forward, the months would proceed in their proper order: Muḥarram, Ṣafar, Rabīʿ al-Awwal... through Dhul-Ḥijjah, and then begin again. This sequence has continued uninterrupted from the time of Ḥajjat al-Wadāʿ to the present day.

❧The Sahaba's Decision: 17 AH

The Prophet ﷺ himself did not establish a formal numbered calendar, he corrected the month sequence but did not institute a year-numbering system. This became an issue approximately fifteen to seventeen years after the Hijra.

Two practical problems arose. First, ʿUmar ibn al-Khaṭṭāb was presented with a contract dispute in his court: a man claimed he was owed money due in Shaʿbān, and the debtor said he had meant next Shaʿbān, and since no year was specified, both were technically correct. A contract that says "Shaʿbān" without specifying a year is ambiguous. Second, Abū Mūsā al-Ashʿarī (or another governor) wrote to ʿUmar asking: "When you send us instructions to complete a project by a certain month, we do not know if you mean this year's month or next year's."

ʿUmar convened a gathering of the senior Companions to address the matter. The question was: what year should serve as Year One?

Several proposals were made:

- The birth of the Prophet ﷺ, rejected

- The death of the Prophet ﷺ, rejected as too sorrowful an event to mark the beginning of a calendar

- The Battle of Badr, proposed as the year Allāh gave the decisive victory

- The Hijra, proposed by ʿAlī ibn Abī Ṭālib

When ʿAlī made his proposal, he argued: "The year of the Hijra is when the situation of the Muslims changed, from dhull (humiliation) to ʿizzah (honor). This was the turning point, the new beginning, the year that the community truly took shape."

The Companions unanimously agreed. ʿUmar said: "Hādha huwa al-raʾy al-sadīd", "This is the sound opinion." And so it was decided: the Islamic calendar would begin with the year of the Hijra. There is no Year Zero, just as there was none in the Roman system. The year of the Hijra is simply Year 1 AH (ʿĀm al-Hijrah, the first year of the emigration).

❧The First Month: Muḥarram

The second question was: which month should be the first month of the year? The existing lunar months already had names; the only question was which would be Month 1.

Again several opinions were given: some said Ramadan (the holiest month), some said Dhul-Ḥijjah (the month of Ḥajj), some said Rajab.

ʿUthmān ibn ʿAffān proposed Muḥarram, and the Companions agreed. Two reasons have been recorded by our classical scholars:

Reason One: The announcement of the Hijra, the second Pledge of ʿAqabah, when the Prophet ﷺ received permission to emigrate, took place after Ḥajj (i.e., Dhul-Ḥijjah). The bulk of the Muhājirūn began emigrating in Muḥarram. The actual departure of the Prophet ﷺ occurred at the very end of Ṣafar and his arrival was in Rabīʿ al-Awwal. So Muḥarram marks the beginning of the emigration season.

Reason Two: For the Companions, Ḥajj was an annual event. Returning from Ḥajj, leaving behind one's sins, beginning a spiritually renewed life, represents a new beginning. The month immediately following the end of Dhul-Ḥijjah is Muḥarram. So Muḥarram carries the energy of fresh beginnings.

Some later scholars additionally noted a reading of Sūrat al-Tawbah 9:108, the verse about Masjid Qubāʾ being built "from the very first day", as a possible Quranic pointer to the "first day" of the Islamic era. This is acknowledged as a somewhat imaginative reading (bʿīd), but it has been mentioned by some classical scholars.

The outcome has governed Muslim civilization ever since. Our Islamic calendar, the Hijri calendar, begins in Muḥarram 1 AH, corresponding to July 622 CE in the Gregorian calendar. It is a pure lunar calendar: 12 months of approximately 29–30 days each, totaling 354 days per year, approximately 11 days shorter than the Gregorian solar year. This means the Islamic calendar rotates through the seasons over a 33-year cycle.