The Umm al-Qura Calendar Explained

The Umm al-Qura calendar is the official Hijri calendar of Saudi Arabia, named after Umm al-Qura University in Makkah, whose astronomers compute it. It is the most widely used calculated Islamic calendar in the world and the one HijriTime follows.

A calendar fixed in advance

Unlike a calendar that waits for the crescent to be seen, the Umm al-Qura calendar decides the length of every month in advance from astronomical data. That makes it possible to print calendars, schedule government business and convert dates years ahead, which is exactly what a civil calendar needs.

The rule used today

Since 1423 AH (2002 CE), a month begins on the evening of the 29th if, as seen from Makkah, two conditions are met on that day:

• the geocentric conjunction (new moon) happens before sunset, and
• the moon sets after the sun.

If both are true, the next day is the 1st of the new month; otherwise the current month is completed to 30 days. Earlier periods used other rules, and Dutch astronomer Robert van Gent of Utrecht University has documented their history in detail.

Calculation is not the same as sighting

The Umm al-Qura rule only requires the moon to be above the horizon at sunset. On many evenings that is true, but the crescent is still too young and too close to the sun to be seen. So Umm al-Qura months often begin a day before the crescent can actually be observed.

For this reason, Saudi Arabia does not use the Umm al-Qura dates alone for the start of Ramadan, Shawwal (Eid al-Fitr) and Dhu al-Hijjah (Hajj and Eid al-Adha). For those months the Supreme Court announces the start after receiving sighting testimony, and the announced date can differ from the printed calendar.

Range of the tables

The published Umm al-Qura tables cover 1356 to 1500 AH (1937 to 2077 CE). For dates outside this range, converters, including ours, fall back to the arithmetical (tabular) Islamic calendar, which uses a fixed 30-year cycle with 11 leap years of 355 days.

Why HijriTime uses it

A website needs a single, predictable date that is the same for every visitor and can be calculated for any year. The Umm al-Qura calendar provides that and matches the official calendar of the country of the two holy mosques. Where your community starts a month by sighting, the actual date may be one day later, and we note this throughout the site. Try it in the Hijri date converter or the Hijri calendar.