The Islamic Calendar

There are only few sources about the calendars used on the Arabian peninsula in pre-Islamic times, especially for central Arabia. In what is now Yemen probably a modified Julian calendar was in use with a year beginning in April. For central Arabia it is known that there were four "forbidden" months in which warfare had to cease, for instance. Sure 9 of the Qur'an states that the number of months in a year is twelve and rejects any "shifting" (nasi). The word nasi does not necessarily designate the insertion of an additional month, which would suggest the existence of lunisolar calendars in pre-Islamic Arabia. But probably only religious feasts were moved from one month to the next according to certain circumstances.

The Islamic calendar as it is used today as well as the counting of years according to the Hijra era were introduced at the latest during the reign of caliph 'Umar (caliph 634-644). Already slightely more than a hundred years later, in about 750 Islamic territory strechted from Andalusia in the west to Samarkand in Central Asia in the east. Thus, the calendar being based on moon observations dates could (and can) differ in various areas.

In the 9th century CE science reached a high level in the caliphate, especially during the reign of al-Ma'mun (r. 813-833). For astronomical almanacs schematic versions of the calendar were created, which were used in comprehensive tables and for chronological purposes.

Internal Structure and Era

The year consists of twelve months strictly bound to lunar phases. Names and order of the months are shown in the follwing table(1).

 No. Name 
 Rabi al-Awwal
 Rabi al-Akhir
 Djumada 'l-Ula
 Djumada 'l-Akhira
10  Shawwal
11  Dhu 'l-Kada
12  Dhu 'l-Hidjdja

The beginning of each month was determined by the first visibility of the crescent after new moon(2). The visibility of the crescent depends on the observer's location as well as on the meteorological conditions. Therefore, months of as many as 31 days occurred although a synodic month has a length of about 29.5 days only. An exception is the 9th month of the Islamic year, Ramadan, which is considered as ending with the 30th day latest, presumably because of the strict fasting to be observed during daylight. Despite the uncertainty about the actual last day of a month, days were sometimes counted backwards from a supposed final day.

The era of the Islamic calendar is taken by some to be 15 July 622 CE, others put it one day later on 16 July 622 CE (Julian). It commemorates the move of Muhammad from Mekka to Medina (then called Yathrib), the Hijra. The exact date of the Hijra has not been found so far, but it took place probably about two months later. As for the difference of one day between the two eras in use, that has only theoretical importance calendrically, the beginning of each month being determined by observation.

Schematic Version

A great disadvantage for computations is the observation-based beginning of each month. Future events cannot be dated exactly as the visibility conditions for a certain day and location are not known in advance. Thus, a regular calendar with fixed month lengths and intercalation rules was required especially for astronomical calculations.

To tackle this problem a schematic version of the Islamic calendar was developed with the months having lengths of alternating 30 and 29 days, beginning with the first month Muharram. The last month Dhu 'l-Hidjdja was given a length of 29 days in common years or 30 days in leap years.

 No. NameLength 
1   Muharram 30 30
2   Safar 29 29
3   Rabi al-Awwal 30 30
4   Rabi al-Akhir 29 29
5   Djumada 'l-Ula 30 30
6   Djumada 'l-Akhira 29 29
7   Radjab 30 30
8   Shaban 29 29
9   Ramadan 30 30
10   Shawwal 29 29
11   Dhu 'l-Kada 30 30
12   Dhu 'l-Hidjdja 29 30

To keep the calendar aligned with the moon's phases 11 years of a 30-year-cycle were made leap years. These were the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th, and 29th years(3). The era of this calendar is 16 July 622 (Because days begin with sunset, that moment falls on 15 July 622 already.) Sometimes the counting was begun a day earlier.

Holidays and Feast Days

Canonical holidays are 'Id al-'Adha on 10 Dhu 'l-Hidjdja as well as the end of the fasting period ('Id al-fitr) beginning on 1 Shawwal and lasting three or four days. Besides these two holidays, further feast and remembrance days are observed.

During the whole month Ramadan is strict fasting is observed between sunrise and sunset. During daylight eating and drinking is prohibited. Exceptios are made, e. g. for expecting women, nursing mothers, the ill or old who would have to fast later or donate food for the poor etc. instead.

To Shiite muslims the month Muharram is a mourning period, especially 10 Muharram. This remembers the martyr death of Husain in the battle of Kerbela on 10 Muharram in the year 61 of the Hijra.
During the first years of Islam, still before the hijra, 10 Muharram was assigned to be a fasting day because Moses was said to have fasted on that day. However, after the introduction of Ramadan as a fasting month fasting on 10 Muharram was no more obligatory.

12 Rabi al-Awwal, called Mawlid, is celebrated as the prophet Muhammad's birthday and is an official holiday in many countries. The actual origin is Muhammad's death in the year 11 of the Hijra (first half of June 632 Julian). It was not until the reign of the Fatimid dynasty in the Middle Ages that it was started to be celebrated as a feast day in Egypt. Therefore in some areas 12 Rabi al-Awwal is considered a day of mourning until today.

One of the last five odd nights of Ramadan , most often that of 27 Ramadan, is Lailat al-Qadr in which the first reveal of the Qur'an is said to have taken place.

The full moon night of Shaban (i. e. the one of 15 Shaban) is Lailat al-Bara'at in which sins are pardoned and destiny determined. The night of 27 Radjab is celebrated as the night of the prophet's heavenly journey (Lailat al-Mi'raj).

Tax Year in the Ottoman Empire

Many difficulties arose because the calendar was completely independent from the seasons. Islamic New Year slowly moved backwards through the seasons 11 days a year, while harvest was only possible in late summer and autumn. In the Ottoman Empire, therefore, the tax year was oriented on the Julian calendar, beginning on 1 September until 1677, when the beginning of the tax year was moved to 1 March. However, the salaries were paid according to the Islamic year, which led to difficulties in bookkeeping. In addition, the different lengths of the years required the ommission of a tax year every 33 Julian years, so as to give tax year and Islamic year roughly the same number. In 1872 documents for the following tax year had been printed with the tax year number 1288 instead of the correct 1289, and subsequently the decision was made to count tax years in an unbroken sequence from then on. Since then Islamic year and tax year did not correspond anymore. In 1917 the beginning of the tax year was shifted to 1 March of the Gregorian calendar. Thus, tax year 1333 began on 1 March 1917. The last tax year following this reckoning was 1341, and on 1 January 1926 the Gregorian calendar was introduced.


In most Islamic countries the Gregorian calendar is used in everyday life. Exceptions are Iran and Afghanistan where the Persian calendar is in use.





According to limitations of fonts and browsers regarding characters it is not possible to use a scientific Arab transscription (e. g. that used in The Encyclopaedia of Islam).

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An exception are the Isma'ilites who use fixed month lengths.

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There have been different versions of the leap year pattern, too. Sometimes the 15th year was taken to be a leap year rather than the 16th., and another version had almost totally different leap years within the 30-year cycle.

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   © Holger Oertel 2000-2008; last change: 19 August 2007

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