Arab countries use both the Gregorian and Islamic calendars, with the Islamic calendar being official for the Islamic (Muslim) religion. In countries such as Saudi Arabia, the Islamic calendar is official, requiring that dual calendars be maintained for international business. The Islamic calendar calculates years from the Gregorian calendar year A. D. 622, uses 12 lunar months, and has a year of 353, 354, or 355 days.
The Islamic year is often indicated by the abbreviation A. H. Since the solar year has 365.242 days and the lunar year has 354.37 days, the Islamic calendar retrogresses through all the seasons, on a cycle of 32.5 Islamic years. The Islamic year 1408 A. H. began (1st of Moharram 1408 A. H.) on August 25th, 1987.
Iran has adopted the solar year, but kept the starting year of A.D 622, and the year begins on Naw Ruz, or March 21. Thus, the Iranian year 1374 began on March 21, 1995. The Islamic (Hijri) year consists of twelve purely lunar months.
| Arabic spelling |
English spelling |
Days |
 |
Moharram |
30 |
 |
Safar |
29 |
 |
Rabeeh Al Awwal |
30 |
 |
Rabeeh Al Thaanee |
29 |
 |
Jumaad Al Awwal |
30 |
 |
Jumaad Al Thaanee |
29 |
 |
Rajab |
30 |
 |
Shahbaan |
29 |
 |
Ramadaan |
30 |
 |
Shawwal |
29 |
 |
Zu Al Kehda |
30 |
 |
Zu Al Hijja |
29/30 |
The table abovepresents the most frequent pattern of durations. There are also other patterns for the true lunar calendar; for example, with the 29/30 day durations inverted. In the years 1407, Moharram had 29 days, Safar had 30 days, and so forth, until Zu El Hijja, which had 30 days. For religious reasons, the beginning of a Hijri month is marked not by the start of a new lunar month, but by a physical (i.e., an actual human) sighting of the crescent moon at a given locale. It is the responsibility of the highest Islamic authority in the country (the Mufti) to announce the start of a new Hijri month. That is why the Hijri calendar might differs from one country to another, and might differ from the real time at which the new crescent is born. The actual date of important religious feasts may vary by one day from the above simplification of the lunar calendar. These feasts are national holidays.
- Year start date:The Hijri start date is 1st Moharram
- Week start date: Saturday.
- When the Gregorian calendar is used, month names are translated into Arabic either by simple transliteration or complete renaming, according to country usage.
The 'weekend' is a new notion that has been imported from the occidental world. It has been adopted in different ways in various Arab countries:
- In Saudi Arabia, Algeria, and some Gulf countries, the weekend starts on Thursday morning (or noon) and continues until Friday evening.
- In Egypt, the weekend runs from Friday morning to Saturday evening for business offices, although some establishments close on Friday and/or Sunday.
- In Lebanon, Morocco, and Tunisia, where there is a mixture of definitions, some weekends start on Saturday noon and run until Sunday evening, with a half day of work on Friday to allow for attendance at Islamic religious rites observed at noon.
- In Morocco, the weekend starts on Saturday and continue till the end of Sunday, with a kind of time-out on Friday to allow attendance at Islamic religious rites at noon
- Some states in Malaysia follow the Islamic calendar and consider Thursday and Friday as the weekend, while other states follow the more common practice of having Saturday and Sunday as the weekend.
A portion of a Hijri calendar for the year 1424 mapping Georgian calendar 2003:
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