The Islamic calendar: months, moon sighting and differing dates

The answer involves both the Moon and the rules used to establish a new month. Scholars differ over whether a sighting in one region applies elsewhere, and religious authorities do not all give astronomical calculation the same role. Jordan’s Iftaa Department explicitly recognises the local and wider-sighting positions as a matter of scholarly disagreement. A different date is not, by itself, evidence that another community has disregarded Islam. Jordan Iftaa Department, fatwa 3496.

The religious discussion below draws on the named institutions and Sunni hadith collections cited. It is not an exhaustive account of every Sunni or Shia authority’s calendar rulings.

For everyday planning, those differences make it useful to separate three questions: what does the calendar predict, what has the authority you follow announced, and which evening does the date begin? Keeping those questions separate makes planning much less confusing.

What makes the Islamic calendar lunar?

The Qur’an identifies the phases of the Moon as a means of marking time for people and for pilgrimage. It also states that the year has twelve months, four of them sacred. The calendar is therefore more than a list of annual occasions: lunar timekeeping is part of the framework in which those occasions are understood. Qur’an 2:189; Qur’an 9:36.

Twelve lunar months are about eleven days shorter than a Gregorian year. That is why Ramadan does not remain in February, June or any other Gregorian month: over successive years, it moves earlier through the civil calendar. A Gregorian date from last year is not a reliable way to schedule the same Islamic occasion this year. US Naval Observatory: the Islamic calendar.

The name “Hijri” connects the calendar’s year numbering to the Hijrah, the Prophet Muhammad’s ﷺ migration from Makkah to Madinah. Egypt’s Dar al-Ifta explains that the year of that migration was adopted as the starting point during the caliphate of Umar ibn al-Khattab. Muharram is the first month of the calendar; Ramadan is the ninth, not the beginning of the year. Dar al-Ifta: the Hijra and the Islamic calendar.

The twelve Islamic months, in order

The sequence is:

1. Muharram
2. Safar
3. Rabi al-Awwal
4. Rabi al-Thani
5. Jumada al-Awwal
6. Jumada al-Thani
7. Rajab
8. Sha‘ban
9. Ramadan
10. Shawwal
11. Dhu al-Qa‘dah
12. Dhu al-Hijjah

Source: Dar al-Ifta’s list of the twelve lunar months.

The four sacred months are Muharram, Rajab, Dhu al-Qa‘dah and Dhu al-Hijjah. The Qur’an establishes their number; an authentic hadith, a report of the Prophet’s ﷺ teaching, names them, including the three consecutive months spanning the end and beginning of the year. “Sacred months” is therefore a specific designation, not another name for every month with a familiar religious occasion. Qur’an 9:36; Sahih al-Bukhari 3197.

Ramadan has its own explicit place in the Qur’an as the month of revelation and fasting. Knowing its position between Sha‘ban and Shawwal also helps explain the announcements people hear: establishing the end of Sha‘ban establishes Ramadan’s beginning, while establishing Shawwal ends Ramadan. Qur’an 2:185; Sahih al-Bukhari 1909.

Does an Islamic date begin at sunset or midnight?

An Islamic calendar date begins at sunset, not at midnight. The night comes before the daylight portion of that date. Darul Ifta Birmingham states this distinction directly in its explanation of the Islamic day. Darul Ifta Birmingham, fatwa 03295.

For example, if the daylight portion of an Islamic date falls on a Friday, its night begins at sunset on Thursday. This is an illustration of the date boundary, not an announcement for a particular occasion. When saving an event, write both parts if necessary: “Thursday after sunset” and “Friday daytime.” That is clearer than an unexplained “Friday night,” which can mean something different in ordinary English.

Do not confuse the beginning of the calendar date with the beginning of the daily fast. The Qur’an permits eating and drinking until dawn and then directs that the fast be completed until nightfall. The sunset date boundary does not mean a Ramadan fast starts the evening before. Qur’an 2:187.

Why can a month have 29 or 30 days?

The Prophet ﷺ described a month as sometimes 29 days and sometimes 30. Ramadan is not automatically a thirty-day month, and a twenty-nine-day Ramadan is not an incomplete one. Sahih al-Bukhari 1913.

In the sighting instruction recorded by al-Bukhari, fasting begins with the crescent of Ramadan and ends with the crescent of Shawwal. When the sky is obscured, the narration directs Muslims to complete thirty days of Sha‘ban. This provides a rule for establishing the month; it is not a requirement to keep waiting indefinitely for clear weather. Sahih al-Bukhari 1909.

Be careful with tables that give each month a permanent length. The US Naval Observatory explicitly labels its alternating month lengths as “formal tabular lengths.” A tabular conversion is useful for calculation, but should not be mistaken for a report that a community has established a particular month by sighting. US Naval Observatory: the Islamic calendar.

Is the astronomical new moon the same as the visible crescent?

No. The astronomical new moon is a calculated phase; seeing the young crescent is a separate observational question. The US Naval Observatory explains that the time of new moon can be calculated, while crescent visibility depends on several factors and cannot be predicted with certainty. A moon-phase app displaying “new moon” is not, on its own, a report that the crescent has been seen. US Naval Observatory: crescent Moon visibility.

Soon after new moon, the crescent is thin, low in the western sky after sunset and difficult to distinguish against twilight. Suitable observing conditions and location matter. This is why knowing the Moon’s age does not automatically settle whether someone could see it from a particular place that evening. US Naval Observatory: crescent Moon visibility.

Why do Muslim communities sometimes follow different dates?

They may differ over which sightings count

A local-sighting approach does not necessarily treat a sighting far away as binding. A wider or global-sighting approach gives an accepted sighting beyond the local area a broader application. Jordan’s Iftaa Department describes both positions, including the distinction some jurists make between nearby and distant regions. Their disagreement concerns how the evidence applies geographically, not whether the Islamic calendar has twelve months. Jordan Iftaa Department, fatwa 3496.

An important narration is Kuraib’s account of Ramadan in Syria and Madinah. He reported a sighting in Syria on the night preceding Friday; Ibn Abbas said they had seen the crescent in Madinah on the night preceding Saturday and would continue according to their own count or sighting. The narration is a central text in discussions of regional differences. It should be read alongside scholarly explanation, rather than used to pretend that no disagreement exists. Sahih Muslim 1087.

They may give calculation different roles

The geographical reach of a sighting is one question; the role of calculation is another. “Sighting versus calculation” does not always describe two entirely separate methods. The International Islamic Fiqh Academy’s 1986 resolution requires sighting while allowing help from astronomical calculations and observatories. Calculation can therefore form part of a sighting-based process without replacing the sighting requirement. IIFA, resolution 18 (6/3).

Singapore follows a different stated approach. MUIS explains that it uses imkanur rukyah, a calculation-based assessment of the possibility of crescent visibility, in the context of frequently cloudy conditions. Its explanation distinguishes that method from the actual-sighting approach used by other regional authorities for key months. This is an example of an authority’s method, not a claim that every scholar accepts the same role for calculation. MUIS statement, 9 April 2023.

These distinctions matter when comparing announcements. Ask what evidence each authority accepts and what area its decision covers before concluding that two different dates amount to a simple factual contradiction.

Which date should you follow?

Start with the recognised religious authority responsible for your community. Egypt’s Dar al-Ifta, for example, advises residents to follow the decision in their country rather than begin or end fasting according to a conflicting foreign announcement. That is its stated fatwa, or religious ruling, not a claim here that every jurisdiction has an identical institutional arrangement. Dar al-Ifta, fatwa 6190.

If you live somewhere without one shared authority, ask your trusted local mosque or qualified scholar which body it follows and how it handles differing announcements. Do this before the last evening if you can. The practical aim is to know where your decision will come from, rather than assemble a personal ruling from whichever messages arrive first.

If travel leaves you between communities following different dates, ask a qualified scholar about your circumstances. Give your departure and arrival dates and the fasting days involved. A general calendar guide cannot resolve every individual case.

How to use advance calendars without treating estimates as announcements

A published calendar and a month-start announcement are different kinds of information. MUIS, for example, publishes annual calendars and separately issues announcements identifying the start of a month for Singapore. Its Shawwal announcement in 2026 explained the visibility assessment and the completion of thirty days of Ramadan. MUIS calendar resources; MUIS Shawwal announcement, 19 March 2026.

For planning, record the source, location and status beside the date. “Estimated, awaiting the authority we follow” is useful where that authority requires later confirmation. Where an authority adopts a calculated calendar, describe that method accurately instead of calling all advance dates unreliable. The differing roles of calculation described above are precisely why a single disclaimer cannot explain every calendar. MUIS explanation of its method; IIFA resolution 18 (6/3).

For leave requests or family arrangements, keep room for the decision you expect to follow. Once it is announced, update your saved date and include the preceding sunset where relevant. Check the year and issuing authority before forwarding an announcement.

One final limit matters: a calendar entry is not proof of an exact, universally known date for Laylat al-Qadr. The Prophet ﷺ instructed Muslims to seek it in the odd nights of Ramadan’s last ten days. Plan for that search rather than letting a single highlighted square replace it. Sahih al-Bukhari 2017.

A calendar is most useful when you understand its method, locality and status and use it alongside the guidance of the authority you trust. A confidently displayed date alone does not provide that context.

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Related reading: Ramadan hub · Why do Ramadan and Eid dates differ? · Fasting in Islam: obligations, exemptions and missed fasts. Browse Islamic Calendar articles.