|What is the Islamic Calendar|
The Islamic calendar is a lunar calendar based on 12 lunar months in a year of 354 or 355 days, used to date events in many Muslim countries and used by all Muslims to determine Islamic holy days.
Each numbered year is designated either H for Hijra or AH for the Latin anno Hegirae (in the year of the Hijra).
In 638 CE (17 AH), Abu-Musa radhiallahu anhu complained about the absence of any dating system in the correspondence he received from Umar radhiallahu anhu, making it difficult to determine which instructions were most recent. Umar radhiallahu anhu then introduced a calendar system for Muslims after debating with his Counsellors, and started the calendar with the date of the Prophet sallallahu alaihi wa sallam’s arrival at Madina (Hijra). Uthman radhiallahu anhu suggested starting the calendar with the month of Muharram.
According to calculations, the first day of the first year corresponded to Friday, July 16, 622. Because of the Hijra event, the calendar was named the Hijra calendar. The first surviving use of it is on a papyrus from Egypt in 22 AH.
In the Islamic calendar each month has either 29 or 30 days, with the first of each month being the day (beginning at sunset) of the first sighting of the new crescent shortly after sunset. If it is not observed due to clouds for example, then the month is 30 days. A sighting has to be made by one or more trustworthy men testifying before a committee of Muslim leaders. Sighting the moon is still followed in the overwhelming majority of Muslim countries with each doing its own monthly observation of the new moon before declaring the beginning of a month on its territory.
Determining the most likely day the crescent could be observed was a motivation for Muslim interest in astronomy, which put Islam in the forefront of that science for centuries. A Hijri year is between 10 and 12 days shorter than a Gregorian year.
For a very rough conversion of Gregorian to Hijri years subtract 622 from the Gregorian year and multiply by 0.97. We also have a link to an online calculator on our site.