What Is the Hijri Calendar? How the Islamic Year Works

The Hijri calendar is the Islamic lunar calendar. It has 12 months that follow the cycles of the moon, so each month lasts 29 or 30 days and the year has 354 or 355 days. Years are counted from the Hijra, the migration of the Prophet ﷺ from Makkah to Madinah in 622 CE, and are written with the suffix AH. Muslims use it to date Ramadan, the two Eids, the Hajj and other acts of worship.

Key Takeaways

• A Hijri month begins with the first visible crescent after the new moon, or by a calculated rule, and lasts 29 or 30 days.
• A Hijri year has 354 or 355 days, about 11 days fewer than a solar year, so Islamic dates move through the seasons.
• Year 1 AH began on 16 July 622 CE (Julian calendar), the year of the Hijra.
• Each Islamic day begins at sunset, not at midnight.
• Communities use different methods to start a month, so the same festival is usually a day apart between them and sometimes more.

A calendar built on the moon

Each Hijri month begins with the thin crescent that appears in the western sky after sunset, a day or so after the astronomical new moon. The US Naval Observatory's overview of the Islamic calendar describes months that "begin when the thin crescent Moon is actually sighted in the western sky after sunset." Some communities use that sighting itself and others a calculated rule based on it, as explained further down.

The Quran ties the count of time to the moon. In Surah Yunus 10:5, it says of the moon (Saheeh International translation of the meaning) that Allah "determined for it phases - that you may know the number of years and account [of time]." In Surah al-Baqarah 2:189, the crescent moons are called "measurements of time for the people and for ḥajj [pilgrimage]."

The number of months is fixed at twelve. Surah at-Tawbah 9:36 begins, in the Saheeh International translation: "Indeed, the number of months with Allāh is twelve [lunar] months in the register of Allāh." The same verse says four of them are sacred.

Unlike the Hebrew or Chinese calendars, the Hijri calendar never adds a leap month to keep pace with the sun. The next verse, Surah at-Tawbah 9:37, opens with "Indeed, the postponing [of restriction within sacred months] is an increase in disbelief," referring to a pre-Islamic practice known as nasi'.

The twelve Hijri months

The months always come in the same order. Encyclopaedia Britannica's entry on the Islamic calendar lists them from Muharram to Dhu al-Hijjah. The four sacred months that Muslims identify from 9:36 are Muharram, Rajab, Dhu al-Qi'dah and Dhu al-Hijjah.

The table shows each month of 1448 AH (June 2026 to June 2027) with its start date in the Umm al-Qura calendar, the calculated calendar Saudi Arabia uses for civil purposes. Dates in this article are calculated from the Umm al-Qura tables in the open-source hijri-converter library that this site uses, and they match the dates R.H. van Gent of Utrecht University lists for the principal Islamic days of observance. Each listed date begins at sunset on the evening before.

These are civil, calculated dates. In a community that follows a sighting, any month may turn out one day longer or shorter. The Islamic months page has a page for each month with its full calendar.

How long is a Hijri year?

A Hijri year has either 354 or 355 days. The moon takes about 29.5 days to go from new moon to new moon, according to NASA's guide to moon phases. A lunar cycle is not a whole number of days, so months alternate between 29 and 30 days, in an irregular pattern, to stay in step with the moon.

By the calculated calendar, 1447 AH had 355 days, 1448 AH also has 355, and 1449 AH has 354. The guide to 354, 355 and leap years explains where the extra day comes from.

Because the lunar year is shorter than the solar year, Islamic dates arrive about 11 days earlier each Gregorian year. The USNO page puts it this way: "the Islamic year shifts earlier in each civil year" by about 11 days. Here is that drift for the calculated start of Ramadan:

The shift is not exactly the same each year because the Hijri year varies by a day and the Gregorian year has leap days. Over about 33 solar years, Ramadan and every other month passes through all four seasons. Why Islamic dates move each year works through the arithmetic.

Counting from the Hijra: what AH means

Hijri years are numbered from the year of the Hijra, the migration of the Prophet ﷺ from Makkah to Madinah. AH stands for the Latin Anno Hegirae, "in the year of the Hijra." The USNO gives the first day of the era, 1 Muharram 1 AH, as Friday 16 July 622 CE in the Julian calendar.

The starting point was chosen by the Prophet's companions. In Sahih al-Bukhari 3934, Sahl bin Sa'd reports that they did not count from the day the Prophet ﷺ was sent as a messenger or from his death, but from his arrival in Madinah. Britannica dates the formal adoption to 639 CE, when the second caliph, Umar ibn al-Khattab, introduced the Hijra era and began year 1 with 1 Muharram, the first month of that lunar year. The migration itself did not take place on 1 Muharram. The story of that decision is told in how Umar adopted the Hijri calendar.

A Hijri year number is not the Gregorian year minus 622. Because Hijri years are shorter, the gap closes slowly: 1448 AH began on Tuesday 16 June 2026, and 1449 AH begins on Sunday 6 June 2027 by the calculated calendar.

The Islamic day begins at sunset

Each Hijri date starts at sunset and runs until the next sunset. The USNO's table of Islamic observances states that its dates "begin at sunset of the previous evening and end at sunset on the date tabulated."

This matters most for evenings. The calculated 1 Ramadan 1448 falls on Monday 8 February 2027, so the month begins at sunset on Sunday 7 February. The first night prayers of Ramadan are on that Sunday evening, and the first fast is on Monday. The reasoning behind sunset as the boundary is covered in why the Islamic day begins at sunset.

Sighting or calculation: how a month starts

Muslims differ on how to know that a new month has begun. Astronomy can give the moment of the new moon exactly, but that is not the same as the crescent being visible. The USNO's page on crescent visibility says the time of each new moon "can be computed exactly," while the first sighting "cannot be predicted with certainty." It depends on sky conditions, the observer's location and experience, and the moon's position.

Three broad approaches

• Local sighting. The month begins when the crescent is seen in the region, or after 30 days if it is not seen.
• Sighting elsewhere. A sighting reported from another country, often Saudi Arabia, is accepted locally.
• Calculation. A rule decided in advance fixes the start of each month, so dates can be published years ahead.

Which method to follow is a religious question on which qualified scholars have taken different positions. For a personal decision, ask a scholar you trust or follow your local mosque. The main arguments on each side are laid out in moon sighting vs calculation.

The Umm al-Qura calendar

Saudi Arabia's Umm al-Qura calendar is the best-known calculated calendar, and its role is often misunderstood. Van Gent describes it as the calendar used by the government of Saudi Arabia for civil purposes. Since 1423 AH (2002), its rule on the 29th day of a month has been that the geocentric conjunction occurs before sunset and the moon sets after the sun at Makkah; if either condition fails, the month runs to 30 days.

The religious dates are a separate matter. Van Gent notes on his table of observances that the dates of Muharram, Ramadan, Shawwal and Dhu al-Hijjah "are often adjusted by the religious authorities of Saudi Arabia after reported sightings of the lunar crescent." So the start of Ramadan and the Eids in Saudi Arabia is announced from sighting reports, and the calculated date is a forecast until then. His introduction to the Umm al-Qura calendar adds that festival dates observed by different communities can "differ by one, two or even three days." The Umm al-Qura calendar explained covers its history and rules.

Other calculated calendars

Other bodies calculate with different criteria. The Fiqh Council of North America's calendar page says it starts a month when, at sunset somewhere on Earth after the conjunction, the moon is at least 8 degrees from the sun and at least 5 degrees above the horizon. It describes physical sighting as "not necessary, but rather a method for confirming the start of a new month." Many other scholars and communities hold that the month must begin from an actual sighting.

Why two calendars can show different dates

Because methods differ, two sources can show different Hijri dates for the same day, and both may be working correctly. A converter based on Umm al-Qura, a converter based on the 30-year tabular calendar, and an announcement based on local sighting can each give a different answer.

The tabular calendar is a simple arithmetic scheme. The USNO notes that it uses a 30-year cycle in which 11 years are leap years, with the extra day added to Dhu al-Hijjah. That gives an average year of 354 11/30 days, close to 12 lunar months, but it does not track the actual moon. It is useful for history and rough conversion, not for announcing Ramadan. Why Hijri date converters disagree shows how to tell which method a tool uses.

The name causes one more mix-up. Iran uses a Solar Hijri calendar, which also counts its years from the Hijra of 622 but follows the sun, so its months stay in the same seasons. According to timeanddate.com's guide to the Persian calendar, it has been Iran's official calendar since 1925, and 1 January 2026 fell in its year 1404, while the lunar Hijri year was 1447. Lunar Hijri vs Solar Hijri compares the two. This article, like most uses of "Hijri," refers to the lunar calendar.

Using the Hijri calendar day to day

As an example, Monday 9 November 2026 was 29 Jumada al-Awwal 1448 AH by the calculated Umm al-Qura calendar. In a community that follows a sighting, the local date may have been a day different.

To work with Hijri dates:

• Check the current Hijri date and the month ahead on the Hijri calendar home page.
• Convert any date in either direction with the Hijri date converter, for example a birthday, a document date or a planned trip.
• Follow the moon through the month on the moon phases page.
• Treat a calculated date for Ramadan, Eid or the Hajj as provisional until the authority you follow confirms it, and remember that the date begins the evening before.