Muslims worldwide utilize the Hijri (lunar) calendar to determine significant religious observances. It features twelve lunar months, each inaugurated by the visible appearance of a new moon. This cyclical method ensures that events such as Ramadan and Eid adjust naturally through the seasons, offering a dynamic spiritual framework inherently tied closely to the moon’s phases.

What is the Islamic calendar?

The Islamic calendar, also called the Hijri or Muslim calendar, is a lunar-based system consisting of twelve months per year, totaling 354 or 355 days. It is central to marking significant religious observances in Islam, including annual fasting during Ramadan and the pilgrimage season for Hajj.

In most Muslim-majority countries today, the Gregorian calendar typically governs civil affairs, but the Hijri calendar retains its primary importance for religious events and rituals. Since 622 CE, when the Prophet Muhammad and his followers migrated from Mecca to Medina, Muslims have recognized this migration—called the Hijrah—as the pivotal moment initiating their calendar era (Anno Hegirae, abbreviated AH). This structured timeline helps Muslims worldwide coordinate religious observances, festivals, and sacred rites.

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Historical Roots

Before Islam, various calendar systems were present on the Arabian Peninsula, especially in the regions of Tihamah, Hejaz, and Najd. While early South Arabian inscriptions show examples of lunisolar calendars, evidence is more scattered for central Arabia.

However, historians know that pre-Islamic Arab tribes distinguished certain “forbidden” (ḥarām) months—four specific months during which warfare was prohibited. These included Rajab, Dhu al-Qa‘dah, Dhu al-Hijjah, and Muharram. Early Byzantine chroniclers also recorded times when Arab tribes paused armed conflict, lending weight to the idea that particular months carried sanctity.

Rajab, Dhu al-Qa‘dah, Dhu al-Ḥijjah, and Muḥarram are considered sacred; fighting or conflict is forbidden during them. These four months were recognized as sacred even before the advent of Islam.

Arabic sources refer to a practice called Nasī’, often translated as “postponement.” Various interpretations exist. Some believe Nasī’ involved a process of intercalation—where an extra month was added occasionally to synchronize the lunar months with the solar year—while others hold it was simply a custom of shifting certain ritual months within the lunar year. Regardless of the precise function, the concept faded once Islam definitively prohibited any practice that altered the purely lunar character of its calendar.

The Emergence of the Hijri Era

Muslim tradition enshrines 622 CE, the year the Prophet Muhammad and his followers migrated from Mecca to Yathrib (later called Medina), as the starting point of the Islamic timeline. This event, known as the Hijrah, signified the foundation of the first cohesive Muslim community (ummah). Caliph Umar ibn al-Khattab (r. 634–644 CE) famously institutionalized this date as the new era’s beginning. From that moment on, Islamic years were counted as Anno Hegirae (AH).

Choosing the Hijrah as the epoch underscored a community-defining transition. Instead of associating each year with a single major event or naming it arbitrarily, as some tribes had done, Muslims standardized and organized years based on the foundation of an Islamic society in Medina. This overcame confusion in correspondence and gave the Islamic world a unifying chronological reference.

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Prohibition of Intercalation

In the tenth year after the Hijrah (AH 10), a Qur’anic verse (9:36–37) banned Nasī’. Many interpret this ban as forbidding intercalation or calendar manipulation, ensuring that the Hijri system would remain strictly lunar. During his farewell sermon, the Prophet Muhammad reiterated that four months are sacred, during which hostilities are forbidden, aligning with pre-Islamic custom but removing any season-based changes.

Nasī’ involved postponing or intercalating months in the pre-Islamic calendar. The Qur’an and Muhammad’s “farewell sermon” forbade Nasī’.

Due to this prohibition, the Hijri calendar cannot align with solar seasons, causing annual observances to “shift” earlier by about eleven days every solar year. This explains why Ramadan, for example, can fall in the summer one decade and in winter a few decades later. Although this might complicate agricultural planning, it maintains the cyclical purity of a purely lunar system.

 

Months and Their Names

The Hijri calendar is composed of twelve months, each traditionally beginning with the visual sighting of a new crescent moon (hilal). Four months—Rajab, Dhu al-Qa‘dah, Dhu al-Hijjah, and Muharram—are regarded as sacred. Their names date back to Arab traditions prior to Islam:

1. Muharram – From “forbidden,” reflecting the prohibition of warfare.
2. Safar – Possibly derived from an emptying of houses when people traveled for resources.
3. Rabi’ al-Awwal and Rabi’ ath-Thani – Terms linked to “spring,” though not literally tied to a particular season.
4. Jumada al-Ula and Jumada ath-Thaniya – From “parched,” referencing weather conditions in older traditions.
5. Rajab – Connected to “remove” or “respect,” historically a month of peace.
6. Sha’ban – Possibly means “to disperse,” marking the time tribes sought water.
7. Ramadan – “Scorching heat”; the holy month of fasting.
8. Shawwal – “Raised,” referencing camels in breeding cycles.
9. Dhu al-Qa’dah – “The one of sitting,” a sacred month discouraging conflict.
10. Dhu al-Hijjah – “The one of pilgrimage,” when Hajj is performed.

Over time, different communities have adapted local names or pronunciations. Pashtuns and Hazaras in Afghanistan used variations of month names in their own languages, while Uyghurs in Xinjiang did likewise, and this pattern has repeated wherever Islam spread, demonstrating how the calendar can integrate local cultures while retaining its fundamental framework.

Observational Method and Day Structure

A hallmark of the Islamic system is the live sighting of the new crescent. If weather conditions or timing prevent the crescent from being seen on the 29th day, the month extends to 30 days. Committees in many Muslim countries gather testimonies from observers, a practice that fosters unity but can sometimes yield variations if different regions declare different sightings.

In Islamic tradition, a new day begins at sunset, not at midnight. Therefore, Friday prayer, known as Jumu’ah, is performed after midday on what is called the sixth day in Arabic naming (al-Jumʿah). In many modern Muslim states, Friday is given as the day off, and some combine it with Saturday or Thursday to form the weekend.

Calculations, Variations, and Adaptations

While many Muslims rely on the traditional sighting method, some countries and jurisdictions use precomputed calendars. Turkey’s Presidency of Religious Affairs (Diyanet) and Saudi Arabia’s Umm al-Qura calendar apply astronomical calculations—such as requiring the geocentric conjunction to occur before sunset—to list months in advance. These approaches reduce uncertainty but do not enjoy universal acceptance due to differing religious opinions on whether calculation can replace direct sighting.

Despite occasional differences in sighting or calculation, the Hijri calendar unites Muslims in shared observances and underscores the faith’s global identity.

A separate but related calendar, the Solar Hijri calendar, is used in Iran and Afghanistan. It also dates from the Prophet Muhammad’s migration but measures time using solar months, ensuring alignment with seasons. Despite sharing the same epoch (622 CE), it diverges from the lunar-based Hijri calendar in day-to-day usage.

Religious Observances and Key Events

Two major Islamic festivals hinge on Hijri dates:

• Eid al-Fitr (1 Shawwal), celebrating the end of Ramadan’s fast.
• Eid al-Adha (10 Dhu al-Hijjah), coinciding with the Hajj rites in Mecca, observing the willingness of Prophet Ibrahim (Abraham) to sacrifice his son.

Ramadan, the ninth month, is observed with daytime fasting and heightened worship. Dhu al-Hijjah, the final month, hosts the pilgrimage (Hajj) to Mecca. These rituals emphasize spiritual reflection and communal solidarity. Because of the shifting nature of the lunar year, Muslims worldwide experience these observances across varying climate conditions over a 33-year cycle.

Muharram, the first month, is among the four sacred months. Shia Muslims especially mark the tragedy of Karbala on the tenth day (Ashura), mourning the martyrdom of Husayn ibn Ali, the Prophet’s grandson. Among Sunnis, Ashura is also significant, reflecting multiple historical events believed to have taken place on that date.

How does the Hijri calendar differ from the Gregorian calendar?

While the Gregorian calendar is solar-based and aligns with the seasons, the Hijri calendar is strictly lunar-based, causing its months to shift about eleven days earlier each solar year. Many predominantly Muslim countries use the Gregorian calendar for civil purposes but retain the Hijri calendar for religious observances.

Usage and Cultural Significance

Although the Hijri calendar remains central to religious life, many Muslim-majority nations have adopted the Gregorian calendar for civil governance, commerce, and international relations. However, official documentation of Islamic holidays, fasting schedules, and other observances adhere to Hijri months. Saudi Arabia, for instance, continued to use the Hijri calendar for government pay until a recent policy change, while countries like Malaysia and Indonesia maintain dual systems, issuing official announcements when Ramadan or Eid begins.

Region-specific calendars sometimes merge Islamic months with older local traditions. In Java, for instance, the Javanese calendar braids pre-Islamic structures into an Islamic framework. Elsewhere, older solar-based agricultural calendars persist concurrently, reflecting the practical needs of farming societies that require seasonal predictability.

From the earliest days in Medina to modern committees scanning horizons, the Hijri calendar preserves an unbroken link to Islam’s foundational events—offering spiritual cadence, cultural identity, and a continuity of tradition that weaves the global Muslim community together across both time and geography.

Differences in interpretation arise when committees in different locales claim sightings on different evenings, thereby starting the month on separate days. In the internet age, these discrepancies become widely visible, sometimes causing confusion regarding Ramadan commencement or Eid celebrations. Various scholarly councils have tried to unify the global Muslim community using a single, calculation-based approach, but consensus remains elusive.

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Frequently Asked Questions about the Islamic Calendar

Why is it called the “Hijri” calendar?

The word “Hijri” comes from the Arabic term for “migration.” It refers to the Prophet Muhammad’s migration (Hijrah) from Mecca to Medina in 622 CE. This event marks the beginning (year 1) of the Islamic timeline.

How are months determined in the Hijri calendar?

Each month starts with the sighting of a new crescent moon (hilal). If, on the 29th day, the crescent is not visible, the ongoing month extends to 30 days, and the next month begins at sunset of the 30th day.

Why does the Islamic year have 354 or 355 days?

Because the Hijri calendar is purely lunar, each month follows a 29–30 day moon cycle. This totals approximately 354 days. Occasional small variations (leading to a 355-day year) arise from how the crescent moon is observed.

Why does Ramadan change dates every year?

A purely lunar year is about 11 days shorter than the solar year. As a result, Ramadan (the ninth lunar month) shifts roughly 11 days earlier each solar year, cycling through all seasons over a 33-year period.

What are the four sacred months in Islam?

Muslims consider Muharram, Rajab, Dhu al-Qa‘dah, and Dhu al-Hijjah as sacred months (ḥarām). Historically, warfare was forbidden during these months.

Why does 1 Muharram mark the start of the Islamic year?

When the need arose for a standardized Islamic era, the second caliph, Umar, chose to begin counting years from the Hijrah—Muhammad’s migration to Medina in 622 CE—and set Muharram as the first month, in alignment with prevailing Arab customs of the time.

Are the months named after something specific?

Yes. Most month names derive from pre-Islamic Arabian customs or seasonal references (e.g., “Rajab” is linked to “removal,” indicating abstention from combat; “Sha‘bān” relates to “scattering,” when tribes would disperse for resources).

Are there differences in how countries use the Hijri calendar?

Yes. While nearly all Muslim-majority countries use the Hijri calendar for religious purposes, most still use the Gregorian calendar for civil and administrative functions. Some regions also utilize local adaptations or calculated methods.

What are the two major Islamic festivals determined by the Hijri calendar?

• Eid al-Fitr (1 Shawwal): Celebrates the end of fasting in Ramadan.
• Eid al-Adha (10 Dhu al-Hijjah): Commemorates the willingness of Prophet Ibrahim (Abraham) to sacrifice his son, observed during the pilgrimage season.

Does the Islamic day start at midnight like the Gregorian day?

No. Each Islamic day starts at sunset and continues until the next sunset. Therefore, Islamic dates and times are aligned with the lunar cycle’s natural transitions, rather than midnight-to-midnight.

What causes variations in month-starts between different Muslim countries?

Differences can arise from weather conditions, astronomy-based calculations, local rules for confirming crescent sightings, or strict reliance on actual physical observations of the moon.

Can astronomical calculations replace crescent sighting?

Opinions vary. Some scholars support calculations to avoid uncertainty, while others adhere strictly to live crescent sightings, viewing the Prophet Muhammad’s instructions on observing the moon as part of religious practice.

What is the significance of the Solar Hijri calendar in some countries?

In places like Iran and Afghanistan, a solar-based Hijri calendar is also used, beginning at the same epoch (622 CE) but measuring months according to the solar cycle rather than moon phases. It ensures alignment with seasons but differs in day-to-day dates from the lunar Hijri calendar.

What is “Nasī’,” and why was it prohibited?

Nasī’ refers to “postponement” in some interpretations—either shifting a month or adding an extra month to align with seasons. It was banned in Islam, preserving the calendar’s strictly lunar nature and ensuring key rituals move throughout the seasons.

How do Muslims number their years in the Hijri calendar?

Years are counted as “AH” (Anno Hegirae), meaning “in the year of the Hijrah.” Thus, the first Islamic year (AH 1) began when the Prophet Muhammad migrated from Mecca to Medina in 622 CE.

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