What Is the Umm al-Qura Calendar?

The Umm al-Qura calendar is Saudi Arabia’s official Hijri calendar, calculated in advance from astronomical data for Makkah instead of waiting for the crescent moon to be seen. It is the most widely used calculated Islamic calendar in the world. This guide explains its month rule, its accuracy, and how it compares with moon-sighting and the tabular Islamic calendar.

What is the Umm al-Qura calendar?

The Umm al-Qura calendar is a calculated lunar Hijri calendar that fixes the start of every Islamic month using the positions of the Sun and Moon at Makkah. Saudi Arabia uses it as its official Hijri calendar for civil and administrative dates.

Umm al-Qura (أم القرى) means “Mother of Towns”, a name the Quran gives to Makkah in Surah al-Anʿam (6:92) and Surah ash-Shura (42:7). The calendar takes its name from the city whose sunset it measures. King Abdulaziz City for Science and Technology (KACST) in Riyadh calculates and publishes the calendar.

Like every Hijri calendar, Umm al-Qura counts 12 lunar months from the Hijrah in 622 CE. The Hijri calendar guide covers that shared foundation; this page covers what makes Umm al-Qura different.

How does the Umm al-Qura calendar decide when a month begins?

The Umm al-Qura calendar checks two conditions at Makkah on the 29th day of each month. A new month starts the next day when the new moon (conjunction) occurs before sunset and the Moon sets after the Sun. Otherwise, the month runs 30 days.

The conjunction is the moment the Moon passes between the Earth and the Sun — the astronomical new moon. Moonset after sunset means the Moon is still above the horizon when the Sun goes down, so a thin crescent is at least present in the evening sky. This two-condition rule has applied since 1423 AH (2002 CE); Saudi authorities used different criteria in earlier decades.

Worked example: Ramadan 1448 (2027)

Ramadan 1448 shows both outcomes of the rule in one month:

• Saturday, 6 February 2027 — 29 Shaʿban. At least one check failed at Makkah, so Shaʿban ran a full 30 days and 1 Ramadan fell on Monday, 8 February.
• Monday, 8 March 2027 — 29 Ramadan. Both checks passed, so Ramadan ended after 29 days and 1 Shawwal (Eid al-Fitr) fell on Tuesday, 9 March.

The same rule runs on the 29th day of every month, which is how Umm al-Qura dates can be printed decades in advance. The Ramadan 2027 guide lists every key date that follows from these two results.

What are the main features of the Umm al-Qura calendar?

The Umm al-Qura calendar produces months of 29 or 30 days and years of 354 or 355 days, all fixed years in advance. Its long-run average month matches the true lunar month to within a few minutes.

Unlike the tabular Islamic calendar, Umm al-Qura follows no fixed pattern of long and short months. In 1448 AH, for example, the months run 29, 30, 29, 30, 30, 29, 30, 30, 29, 30, 29 and 30 days — two 30-day months back to back in two places, because each month follows the real Moon.

How accurate is the Umm al-Qura calendar?

The Umm al-Qura calendar is astronomically precise but does not predict crescent visibility. A Moon that sets just after the Sun is often too thin and too low to be seen, so Umm al-Qura can start a month one day before the crescent is visible by eye.

For this reason, Saudi Arabia does not rely on Umm al-Qura alone for the three months that carry religious obligations. The start of Ramadan, Shawwal (Eid al-Fitr) and Dhu al-Hijjah (Hajj and Eid al-Adha) is announced after testimony of an actual sighting is accepted by the Saudi Supreme Court. Those announced dates usually match Umm al-Qura but can fall a day later.

For ordinary dating — documents, records, birthdays, history — Umm al-Qura is accurate and stable. A date converted today will not change later, which makes it the practical standard for software and converters.

How does Umm al-Qura differ from other Islamic calendars?

Umm al-Qura sits between pure arithmetic and pure observation. The tabular calendar uses a fixed numerical cycle, local moon-sighting waits for the crescent, and Umm al-Qura calculates the real Moon’s position at Makkah.

The tabular Islamic calendar alternates 30- and 29-day months and adds a leap day in 11 years of every 30-year cycle. The Fiqh Council of North America (FCNA) starts a month when the new moon occurs before 12:00 GMT. Local sighting starts a month only after the crescent is seen. Because the methods differ, the same month can begin on different days:

Four of these eight months start a day later in the tabular calendar. Across all 1,212 months from 1400 to 1500 AH, the two calendars start on the same day 57% of the time. The tabular month starts one day later 36% of the time, one day earlier 6% of the time, and two days later in only 12 months. The gap never exceeds two days, because both calendars track the same average lunar month.

Where is the Umm al-Qura calendar used?

The Umm al-Qura calendar is used by the Saudi government for official Hijri dates and by most software that displays Islamic dates. It is the default “Islamic” calendar in many phones, computers and websites.

Microsoft .NET includes an UmAlQuraCalendar class, and the Unicode ICU library — used by Chrome, Firefox, Safari, Android and Node.js — includes the islamic-umalqura calendar. Islamic apps, prayer-time services and online converters, including MultiCalculators, use it for the same reason: one shared, published standard gives the same answer everywhere.

How do you convert dates with the Umm al-Qura calendar?

Convert dates with the Umm al-Qura calendar by using a converter built on its published data. Manual conversion is impractical, because month lengths follow the real Moon rather than a fixed formula.

The converter handles Gregorian-to-Hijri and Hijri-to-Gregorian conversion and Islamic age. For a worked example of Umm al-Qura dates in practice, see Ramadan 2027 dates, or open a single day such as 18 February 2026 in the Hijri calendar.

Frequently asked questions

Is the Umm al-Qura calendar the same as the Islamic calendar?

Umm al-Qura is one version of the Islamic (Hijri) calendar. It uses the same 12 months and year count, but fixes month starts by calculation at Makkah instead of by local sighting.

What does Umm al-Qura mean?

Umm al-Qura means “Mother of Towns”. It is a Quranic name for Makkah, the city whose sunset the calendar uses to decide when each month begins.

Is Ramadan decided by the Umm al-Qura calendar?

Not officially. Saudi Arabia announces Ramadan, Shawwal and Dhu al-Hijjah after a confirmed moon-sighting. Umm al-Qura gives the expected date, which usually matches but can be a day early.

Does the Umm al-Qura calendar have leap years?

Not in a fixed pattern. Each year has 354 or 355 days depending on the real Moon. Between 1400 and 1499 AH, 37 years have 355 days.

Why do Saudi Islamic dates differ from my country’s?

Your country may start months by local sighting or by another calculation rule. Different methods can place the first day of a month one day apart.

How far ahead is the Umm al-Qura calendar calculated?

Umm al-Qura is published years in advance. Software libraries include its dates for well over a century, so future dates can be converted today.

In short, the Umm al-Qura calendar is Saudi Arabia’s calculated Hijri calendar: a month starts after the 29th day only when the new moon comes before sunset and the Moon sets after the Sun at Makkah. It is the stable standard for converting dates, while religious start dates are still confirmed by sighting. To use it, convert a date with the Umm al-Qura converter.

Figures computed from the Umm al-Qura calendar · religious dates may follow local moon-sighting · MultiCalculators.com