Islamic Calendar Explained: The Hijri Year, Month by Month

Quick Answer

• What it is: a lunar calendar of twelve months, with a year of 354 or 355 days
• Where year 1 starts: the Hijrah, the migration to Medina in 622 CE; years are written AH
• How a month begins: with the sighting of the crescent, so a month has 29 or 30 days
• Why dates move: the lunar year is about 11 days shorter than the solar year, and there is no leap month
• Sacred months: four of the twelve, in which fighting is forbidden
• Muharram: the first month in the majority convention, and the month of Ashura

Almost everything confusing about Islamic dates comes from one design decision: the calendar follows the moon and refuses to be corrected back to the seasons.

That single choice explains why Ramadan moves, why a month can be 29 or 30 days, why two countries can start the same month a day apart, and why the year count begins not with a birth but with a migration.

What Is the Islamic Calendar?

The Hijri calendar is a lunar calendar of twelve months in a year of 354 or 355 days. It is the calendar Muslims use to fix religious dates: the month of fasting, the season of pilgrimage, Ashura, and the two Eids. In almost every country with a Muslim majority the civil calendar is the Gregorian one, and the Hijri calendar runs alongside it for religious purposes.

The Quran treats the moon's phases as the mechanism, not as decoration. When the Prophet (PBUH) is asked about the phases of the moon, the answer given is that they are a means for people to determine time and pilgrimage (2:189). Another verse describes the sun and the moon as set in measured phases so that you may know the number of years and the calculation of time (10:5).

Note the wording of that second verse: years and calculation. The calendar is presented as a tool for counting, which is exactly what the community later had to build.

Who Fixed the Year Numbering?

The months are older than the year numbers. Pre-Islamic Arabia named each year after something that had happened in it, and there was no running count at all.

The change came from an administrative complaint. Around 638 CE, an official in Basra wrote to the caliph Umar that the letters arriving from him carried no year, which made it impossible to tell which instruction was the most recent. Umar consulted his advisers and decided that the first year of the new era would be the year of the Prophet's (PBUH) arrival at Medina. The astronomer al-Biruni records Umar as having introduced the year count in 638 CE.

Two things are worth separating here. Umar's decision fixed the era, the point from which years are counted. It did not invent the months, which were already in use with the same names. The calendar was given a starting line, not a new body.

Years in this era are written AH, from the Latin Anno Hegirae, the year of the migration.

Why Do Islamic Dates Move About Eleven Days Each Year?

Because a lunar year is genuinely shorter, and the calendar does not compensate for it.

The average time from one new moon to the next is about 29.53 days. Twelve of those come to roughly 354 days, against 365.24 for a solar year, a shortfall of about 10.9 days. That is the eleven-day drift: an Islamic date falls about eleven days earlier on the Gregorian calendar every year, and the whole cycle of twelve months slides backwards through the seasons in roughly 33 solar years.

The temptation in a farming society is to fix this by inserting an extra month every few years. The Quran rules that out. The verse that establishes twelve months in the sight of God also condemns the practice of reallocating the sanctity of months, describing it as an increase in disbelief, by which people are led astray, adjusting the sacred months one year and upholding them in another (9:37).

So the drift is not a bug that nobody noticed. It is the direct result of a deliberate ruling, and the practical consequence is that Ramadan, Hajj and Muharram all travel through the year over a lifetime.

How Does a Month Begin?

Each month begins with the new lunar cycle, and traditionally that means a sighting.

The classical method is observation of the crescent, the hilal, low in the sky shortly after sunset. If the crescent is seen on the evening of the twenty-ninth day, the next day begins the new month. If it is not seen, the current month is completed at thirty days and the new month starts the day after.

That is why a Hijri month is 29 or 30 days and never a fixed number. It also explains why the start of a month can be announced late: cloud, haze and the exact position of the moon all decide whether a sighting is possible, and a month length can be extended by a day at short notice.

Since the moon sets at different times at different longitudes, a new month can also begin on different days in different countries. Two communities on the same evening can be a day apart and neither is making an error in its own method.

Is There a Calculated Version?

Yes, several, and they exist because people needed to plan ahead.

Muslim scholars developed the tabular Islamic calendar in the eighth century: an arithmetic scheme with months alternating between 30 and 29 days and eleven leap days in every thirty years, so that dates can be known in advance without waiting for a sighting. Some communities, including Bohra and Ismaili groups, follow a tabular scheme rather than a sighting.

States have built their own versions. Saudi Arabia has traditionally used the Umm al-Qura calendar, which is based on astronomical calculation and is used for administrative purposes, and its parameters have been revised more than once. Calculations of this kind and local sighting do not always agree, which is why the first day of a month can differ between countries even when nobody is looking at the sky carelessly.

This is a live methodological argument, not a settled question. Some hold that the text requires sighting; others accept calculation or global sighting. The calendar as actually used around the world reflects that disagreement.

What Are the Sacred Months?

Four of the twelve, and the Quran names their number rather than their names.

The verse is explicit: the number of months ordained by Allah is twelve, and of them four are sacred (9:36). The four are Rajab, which stands alone in the seventh position, and the three consecutive months of Dhu al-Qa'dah, Dhu al-Hijjah and Muharram, in which fighting is forbidden. Muharram's own name means forbidden, and it is sacred for that reason.

The practical weight of this in the mourning calendar is considerable. Muharram is a sacred month and the month in which Hussain (AS) was killed, which is part of why the tradition treats the first ten days with the seriousness it does. For the month itself, see what Muharram means.

The Twelve Months, One by One

The names are pre-Islamic and most of them describe a season or a custom, which is why several no longer match the time of year they point to.

No.	Month	Meaning of the name	What it marks
1	Muharram	forbidden	Sacred month, fighting forbidden; contains Ashura on the tenth
2	Safar	void	Named for houses standing empty while people gathered food
3	Rabi al-Awwal	the first spring	The month the Prophet (PBUH) was born, and the month of the Hijrah
4	Rabi al-Thani	the second spring	Also called Rabi al-Akhir, the last spring
5	Jumada al-Ula	the first of parched land	Often treated as the pre-Islamic summer
6	Jumada al-Akhirah	the last of parched land	The second of the pair
7	Rajab	respect, honour	Sacred month, the one that stands alone
8	Shaban	scattered	When tribes dispersed to find water; the month before Ramadan
9	Ramadan	burning heat	The month of fasting, the most venerated in the calendar
10	Shawwal	raised	Begins with Eid al-Fitr, the end of the fast
11	Dhu al-Qa'dah	the one of truce	Sacred month, war banned
12	Dhu al-Hijjah	the one of pilgrimage	Sacred month; the Hajj, the Day of Arafah and Eid al-Adha fall in it

Does the Hijri Year Start in Muharram for Everyone?

No, and the disagreement is old enough to change the date of Karbala by a year.

In the majority convention the year opens with Muharram, and that is how most of the world, and most reference works, date events. Twelver Shia scholarship holds instead that the new year and first month is Rabi al-Awwal, on the reasoning that the Hijrah itself took place in that month, which is when the era begins.

The consequence is not decorative. Under the Rabi al-Awwal reckoning the battle of Karbala falls in 60 AH; under the Muharram reckoning it falls in 61 AH. Both figures circulate in serious literature. The articles on this site use 61 AH, the convention followed by most historical writing, without claiming that the other count is wrong.

What does not change is the internal structure: Ashura is the tenth of Muharram either way, and the mourning cycle is counted from that day rather than from the new year.

Why Does This Calendar Matter in Muharram?

Because the whole mourning season is a set of dates on it.

Ashura is the tenth of Muharram, the day Hussain (AS) was killed. The first ten days are the period of the majlis, culminating on the tenth, and the fortieth day after it, Arbaeen, is the twentieth of Safar, the next month. When the calendar shifts eleven days earlier each year, the season shifts with it, which is why the mourning cycle has been observed in every season of the solar year by different generations.

The dates are the skeleton; the gathering is the body. For what happens inside those ten days, see what Ashura is, the story of Karbala, and how a majlis runs.

One practical point follows from everything above. Because a month begins with a sighting, the Hijri date you see on a phone or a printed diary is a forecast, not a fact, and the local announcement is what actually decides. Communities that publish yearly calendars in advance are making a calculated prediction, and everyone involved knows it.

Key Takeaways

• The Hijri calendar is lunar: twelve months, 354 or 355 days, no correction back to the seasons.
• Year 1 is the Hijrah of 622 CE, and the era was fixed under the caliph Umar after an official complained that letters carried no dates.
• A lunar year is about 11 days shorter than a solar year, so Islamic dates move earlier each year and cycle in roughly 33 solar years.
• A month begins with the sighting of the crescent, which is why it has 29 or 30 days and can start a day apart in different countries.
• Four months are sacred: Rajab, Dhu al-Qa'dah, Dhu al-Hijjah and Muharram.
• Muharram is the first month in the majority convention; Twelver Shia scholarship places the new year in Rabi al-Awwal, which is why Karbala is dated 60 AH in one reckoning and 61 AH in the other.

Frequently Asked Questions

What is the Islamic calendar called?

The Hijri calendar, also called the Muslim calendar. Its years are written AH, from Anno Hegirae, and its epoch is the migration to Medina in 622 CE.

Why does the Islamic year start in 622 CE?

Because the era was set from the Hijrah, the Prophet's (PBUH) migration to Medina. The caliph Umar fixed it after an official in Basra complained that official letters bore no year, making it impossible to tell which instruction was newer.

Why do Islamic dates change every year?

A lunar year of twelve months is about 354 days, roughly 11 days short of a solar year. The Quran rejects the insertion of a leap month, so the calendar drifts earlier by about eleven days annually and completes a full cycle through the seasons in about 33 years.

Why can a month be 29 or 30 days?

Because the month begins with the sighting of the crescent after sunset on the twenty-ninth evening. If the crescent is not seen, the month is completed at thirty days. Weather and the moon's position decide which happens.

How many months are sacred in Islam?

Four: Rajab, and the three consecutive months of Dhu al-Qa'dah, Dhu al-Hijjah and Muharram. The Quran states that twelve months were ordained and that four of them are sacred, and fighting is forbidden in them.

Is Muharram the first month of the Islamic year?

In the majority convention, yes. Twelver Shia scholarship holds that the year begins with Rabi al-Awwal, the month in which the Hijrah took place, and that is why Karbala is dated 60 AH in that reckoning rather than 61 AH.

Sources

• Wikipedia, "Islamic calendar", on the twelve lunar months and the 354 or 355 day year, the Hijri era and its 622 CE epoch, Umar's introduction of the era after Abu Musa al-Ash'ari's complaint, the sighting of the crescent, the four sacred months, the mean synodic month and the eleven-day drift, the tabular calendar, and the month-by-month table of names and meanings, at Wikipedia.org.
• timeanddate.com, "Islamic Calendar", on the month beginning with the waxing crescent, months of 29 or 30 days, the absence of a leap month, the 33-year cycle, al-Biruni on Umar and the year count, the tabular calendar of the eighth century, and differences between countries, at Timeanddate.com.
• The Quran, Surah At-Tawbah, verse 36, that the number of months with Allah is twelve and four of them are sacred, at Quran.com.
• The Quran, Surah At-Tawbah, verse 37, on the condemnation of reallocating the sacred months, at Quran.com.
• The Quran, Surah Al-Baqarah, verse 189, that the phases of the moon are a means to determine time and pilgrimage, at Quran.com.
• The Quran, Surah Yunus, verse 5, on the sun and moon set in measured phases so that the number of years and the reckoning may be known, at Quran.com.
• Wikipedia, "Arba'in", on the fortieth day after Ashura coinciding with the twentieth of Safar, at Wikipedia.org.

Disclaimer: This article separates the mechanics of the calendar, the historical record of how the era was fixed, and the disagreements that remain live among communities: sighting against calculation, and the question of which month opens the year. On those points it reports the positions rather than ruling between them. Dates given for events use the 61 AH convention followed by most historical writing. If you find an error, write to us through the contact page and we will correct it.