An Islamic calendar is a calendar that is based on Islamic religious guidance and it is used by Muslims in the Muslim world. This calendar starts from the beginning of Islam and that year will be marked by the sighting of the crescent moon at the head of the new month. This feature has given rise to the idea of an Islamic calendar. The starting date is taken from the sighting of the crescent moon and this has been followed by the Muslims ever since.

There are two calendars that have been made available for Muslims. These calendars are the Islamic calendar and the Gregorian calendar. These two calendars have a difference in some details.

The Islamic calendar is called in Arabic as I'tikaf and the Gregorian calendar is called in Latin as L'lmer. The difference between the two calendars is that the Islamic calendar is more rigid in its details and is based on the lunar, solar and a little bit of terrain. The geographical factors that go into the calculation of the lunar phase count the lunar months. Solar phase are important because they are considered to be more accurate than the lunar phase.

The Islamic calendar follows the Islamic lunar calendar and is also referred to as 'al-Hijri'. However, it does not follow solar, but rather a terrestrial-based lunar cycle.

An Islamic calendar starts from the first day of the month of Shawwal. That is the day that the crescent moon was seen over the mosque at Makkah. In the beginning of the month, the Islamic calendar is the same as the Gregorian calendar and follows the same rules for keeping track of dates.

With the advent of internet, many localities have adopted the calendar that is a variation of the Islamic calendar. This includes Alaska, Bahrain, Canada, Costa Rica, Croatia, Egypt, Iran, Iraq, Lebanon, Oman, Saudi Arabia, Sudan, United Arab Emirates, United Kingdom, Yemen, and United States. It has the exact same features that the other versions of the Islamic calendar have but this one is more amenable to the needs of people living in various locations.

These calendars have different features as well. One difference that can be seen in both is that the Islamic calendar has no leap year. Leap years have a date that is at least three months after the previous calendar. On the other hand, the Gregorian calendar has leap years and these dates are included as part of the year and they follow the same rules that the Islamic calendar follows.

A lot of calculations that are used for everyday life use the Islamic calendar. To calculate the banking and stock markets, to select the market figures, to prepare the dates for the games, the school and university entrance exams, and the list goes on. This is a great calendar that is used around the world and that has only an Islamic basis.