What Is the Hijri Calendar?

The Hijri calendar is the lunar calendar used by Muslims to determine religious dates. It begins with the Hijrah, the migration of the Prophet Muhammad (peace be upon him) from Mecca to Medina in 622 CE.

Unlike the Gregorian solar calendar, the Hijri calendar follows the moon. This means Islamic dates move backward through the seasons by about ten or eleven days each year, so a date such as the first day of Ramadan gradually cycles through every season of the Gregorian year over roughly three decades.

The calendar is also known as the Islamic calendar or the Muslim calendar, and its year is abbreviated AH, from the Latin Anno Hegirae ("in the year of the Hijrah"), just as Gregorian years are marked CE or AD.

The Hijrah and the Origin of the Calendar

The calendar's starting point is not the birth of the Prophet Muhammad or the beginning of revelation, but the Hijrah — his migration with a group of early Muslims from Mecca to the city of Yathrib, later renamed Medina, in 622 CE. This migration marked a turning point: it was in Medina that the first Muslim community was established with its own social and legal structure.

The decision to date the calendar from the Hijrah rather than another event is generally attributed to the second caliph, Umar ibn al-Khattab, who is widely reported to have set the calendar's start point during his rule, roughly two decades after the Hijrah itself, once officials needed a consistent system for dating correspondence and administrative records across a rapidly expanding Muslim territory. Choosing the Hijrah rather than the Prophet's birth or death reflected its significance as the founding moment of an organised Muslim community rather than a purely personal milestone, and this choice has shaped how Muslims understand the calendar ever since — not as a record of one life, but as a marker of a shared communal beginning.

The Lunar Year vs. the Solar Year

A lunar year has about 354 or 355 days, while a solar year has about 365.25 days. The difference of roughly eleven days causes Ramadan, Hajj, and Eid to shift through the seasons over a 33-year cycle.

This shifting has practical effects. Muslims may fast Ramadan in long summer days one year and short winter days a few years later. Pilgrims performing Hajj also experience different weather conditions depending on where in the cycle a given year falls.

Each Hijri month is defined by the cycle of the moon from one new crescent to the next, roughly 29.5 days, which is why months alternate between 29 and 30 days rather than following a fixed pattern like the Gregorian calendar's 28-to-31-day months. This lunar basis is explicitly described in the Qur'an, which states that the moon has been made a means for people to know the number of years and the reckoning of time.

The Twelve Months of the Hijri Calendar

The Islamic year has twelve months: Muharram, Safar, Rabi' al-Awwal, Rabi' al-Thani, Jumada al-Awwal, Jumada al-Thani, Rajab, Sha'ban, Ramadan, Shawwal, Dhul-Qa'dah, and Dhul-Hijjah.

Four of these months are considered sacred: Muharram, Rajab, Dhul-Qa'dah, and Dhul-Hijjah. Fighting was traditionally forbidden during them, and Muslims are encouraged to increase good deeds. Three of the four sacred months fall consecutively around the Hajj season (Dhul-Qa'dah, Dhul-Hijjah, and Muharram), historically providing pilgrims safe passage to and from Mecca, while Rajab stands alone earlier in the year.

Some months carry specific religious significance beyond the sacred four. Ramadan, the ninth month, is the month of fasting. Shawwal follows immediately and includes Eid al-Fitr on its first day. Sha'ban, the month before Ramadan, includes the night of the middle of Sha'ban (Nisf Sha'ban), observed by some communities with additional worship, and is traditionally a time when Muslims begin preparing spiritually for the fast ahead.

The names of the months themselves carry historical meaning from pre-Islamic Arabia, where they were already in use as a lunar calendar before Islam adjusted their significance. "Muharram" means "forbidden," referring to its status as a sacred month in which fighting was prohibited. "Ramadan" is linked to an Arabic root associated with intense heat, reflecting the season in which the name was fixed in the pre-Islamic calendar. "Rabi'" relates to spring, and "Jumada" to dryness — names that originally tracked the season in which each month fell, before the calendar became strictly lunar and the months began drifting independently of the seasons. Understanding this background helps explain why the month names do not describe the current season a given Hijri month falls in today, even though their names originally reflected exactly that connection thousands of years before the strictly lunar system fixed itself in place.

The Historical Spread of the Hijri Calendar

The Hijri calendar spread alongside the rapid expansion of Muslim-governed territory in the seventh and eighth centuries CE, becoming the standard dating system on coins, official correspondence, land records, and monumental inscriptions across a territory that eventually stretched from Spain to Central Asia. Historians and epigraphers today rely heavily on Hijri dates inscribed on early Islamic coins and buildings to establish accurate chronologies of the early Muslim world, since these inscriptions are often the most precisely dated primary sources available from the period.

Some of the earliest surviving dated Islamic artefacts, including coinage from the late seventh century CE, bear Hijri years and are among the tools scholars use to cross-reference political and social developments across the early Islamic empires with more certainty than reconstructed oral or later-written histories alone would allow. This makes the Hijri calendar not just a religious tool but also a historical anchor still used in modern academic research on early Islamic civilisation.

As Muslim rule extended into regions with their own established calendars — Persian, Byzantine, and later others — the Hijri calendar often existed alongside local systems for centuries, used specifically for religious and legal purposes while regional administrations sometimes retained older solar calendars for agricultural and fiscal record-keeping. This dual-calendar pattern, where the Hijri calendar governs worship while another calendar governs civil or agricultural life, is essentially the same pattern seen in many Muslim-majority countries today, including the Gulf states, where the Gregorian calendar now plays the role once played by regional solar calendars.

Some solar variants of the Hijri calendar were also developed historically for regions where a purely lunar calendar was less practical for agriculture and taxation, most notably the Solar Hijri calendar still used today as the official civil calendar in Iran and Afghanistan. This calendar keeps the same starting point — the Hijrah — but tracks the solar year rather than the lunar cycle, meaning its dates stay fixed relative to the seasons, unlike the lunar Hijri calendar used for Islamic religious dates.

Moon Sighting or Astronomical Calculation?

Traditionally, each month begins when the new crescent moon is sighted after sunset, a practice rooted in a hadith instructing Muslims to begin and end the Ramadan fast based on sighting the crescent. Today, many countries combine visual sighting with astronomical calculation.

Saudi Arabia and several Gulf states use the Umm al-Qura calendar, which is based on astronomical calculations, for civil planning and government scheduling, while still relying on moon-sighting committees to formally confirm the start of religiously significant months such as Ramadan and Shawwal. Other communities and countries prefer physical moon sighting exclusively, which can lead to slight differences in start dates between regions — meaning Eid may be celebrated on different days in different countries in the same year, a normal and long-recognised feature of the lunar calendar rather than a disagreement about religious practice itself.

This diversity of method has led to ongoing debate among scholars and astronomers about whether calculation alone should be sufficient, or whether physical sighting remains necessary, with credible positions on both sides and no single global authority mandating one method for all Muslims.

Periodically, proposals have been raised for a single, globally unified Hijri calendar based purely on calculation, which would allow Islamic dates to be predicted decades in advance with full certainty, similar to how Gregorian dates are fixed. Supporters argue this would simplify planning for millions of Muslims worldwide and reduce the year-to-year uncertainty around exact holiday dates. Critics, including many traditional scholars, argue that reliance on physical sighting has strong scriptural and historical grounding and that local sighting practices reflect legitimate regional religious authority rather than a problem to be engineered away. No consensus has been reached, and in practice most Muslim-majority countries continue to combine calculation for planning purposes with sighting-based confirmation for the religiously significant months.

How the Hijri Calendar Shapes Worship

All major Islamic acts of worship are tied to the Hijri calendar. Ramadan falls in the ninth month. Hajj and Eid al-Adha occur in Dhul-Hijjah. Ashura fasting is observed on the tenth of Muharram, and the Islamic New Year begins on the first of Muharram — our guide to Islamic New Year celebrations covers this in more detail. Laylat al-Qadr, widely regarded as the holiest night of the year, falls within the last ten nights of Ramadan; see our guide to Laylat al-Qadr for more.

Understanding the calendar helps Muslims prepare spiritually and logistically for these events. It also connects them to the historical Hijrah, which gave the calendar its name, and reinforces a sense of shared time that spans the entire Muslim world regardless of local civil calendars.

Converting Between Hijri and Gregorian Dates

There is no fixed one-to-one mapping between Hijri and Gregorian dates because the years are different lengths. Online converters and official calendars can estimate dates, but the exact start of a month depends on moon sighting or official announcement, so converters typically provide an approximate date that may shift by a day depending on the country and method used.

Most Hijri-Gregorian conversion tools use an arithmetic approximation known as the tabular Islamic calendar, which follows a fixed 30-year cycle of alternating 354- and 355-day years to approximate the average lunar year with reasonable accuracy over long periods. This is useful for historical research, scheduling far in advance, or software applications, but it is explicitly an approximation rather than a religiously authoritative determination of any specific month's start — for that, official announcements remain necessary. Travellers, businesses, and researchers planning years ahead commonly rely on this tabular approximation while building in a buffer of a day or two around religiously significant dates to account for the final, sighting-based confirmation.

For important religious dates, it is best to check announcements from local religious authorities or the country you live in, rather than relying solely on a fixed conversion tool, especially for dates that determine the start of Ramadan, Eid, or Hajj.

The Hijri Calendar in the UAE and Saudi Arabia Today

In the UAE and Saudi Arabia, both the Hijri and Gregorian calendars are used side by side. Government documents, some official holidays, and religious observances are dated using the Hijri calendar, while day-to-day business, banking, and most civil administration commonly use the Gregorian calendar. National moon-sighting committees in Saudi Arabia and the UAE announce the start of key months, particularly Ramadan and Dhul-Hijjah, and these announcements are widely reported by local media each year.

Public and private sector employers in both countries typically adjust annual holiday calendars each year to reflect the Hijri dates for Islamic holidays, since these dates move relative to the Gregorian calendar. Many government portals in the UAE and Saudi Arabia publish converted Hijri-Gregorian calendars annually to help residents plan around religious holidays, school terms, and public holidays in advance.

Businesses across the Gulf also plan around the Hijri calendar in practical ways. Retailers anticipate seasonal demand shifts around Ramadan and the two Eids, banks and government offices adjust working hours during Ramadan, and the tourism and hospitality sectors plan capacity around Hajj and Umrah seasons, when millions of pilgrims from around the world pass through Saudi Arabia. Because these dates shift roughly eleven days earlier every Gregorian year, businesses that operate on multi-year plans have to recalculate the expected Gregorian dates for major Islamic events regularly rather than assuming they fall in the same month each year.

Frequently Asked Questions

Why is the Islamic calendar called Hijri?

It begins from the year of the Hijrah, the migration of the Prophet Muhammad from Mecca to Medina in 622 CE.

How many days are in a Hijri year?

354 or 355 days, depending on whether the months are 29 or 30 days long.

Why do Ramadan and Eid move earlier each Gregorian year?

Because the Hijri lunar year is about eleven days shorter than the solar year, causing Islamic dates to shift roughly eleven days earlier on the Gregorian calendar each year.

Can Hijri dates be predicted in advance?

Astronomy can estimate dates, but the official start of a month often depends on moon sighting or national announcements, so predicted dates are usually treated as approximate until confirmed.

Is the Hijri calendar used officially today?

Yes, many Muslim-majority countries use it alongside the Gregorian calendar for religious and sometimes civil purposes, including Saudi Arabia and the UAE.

Who decided the Hijrah would mark year one of the calendar?

The calendar's starting point is widely attributed to the caliph Umar ibn al-Khattab, who established it roughly two decades after the Hijrah for administrative purposes.

Why do some countries celebrate Eid on different days?

Because the start of a lunar month depends on moon sighting or calculation, which can vary slightly by location and method, some countries confirm a new month a day earlier or later than others.

What does "AH" mean next to a Hijri year?

AH stands for the Latin phrase Anno Hegirae, "in the year of the Hijrah," and is used the same way CE or AD is used with Gregorian years, for example 1447 AH.

Do the Hijri month names describe the current season?

No. Several month names originated from the season in which they fell in the pre-Islamic calendar, but because the Hijri calendar is strictly lunar, the months now rotate through all seasons over time and no longer match their original seasonal meaning.

Sources

  1. Encyclopaedia Britannica — Islamic calendar
  2. Time and Date — Islamic calendar
  3. Islamicity — Hijri calendar and history
  4. Umm al-Qura calendar, Saudi Arabia — official astronomical calendar reference.
  5. IslamQA — moon sighting and the start of Hijri months

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