Moon Sighting vs Calculation: How a Hijri Month Starts

Muslims use two broad ways to decide when an Islamic month begins. Moon sighting means waiting for a reliable report that the new crescent (the hilal) was actually seen after sunset on the 29th; if it is not seen, the month runs to 30 days. Calculation means fixing the start in advance from astronomical data, using a stated rule about the Moon's position. Within sighting, communities also differ on whose sighting counts: one from their own region, or one from anywhere. These positions are long-standing differences of scholarly opinion, and they are the main reason Ramadan and Eid can start on different days in different places.

Key Takeaways

• The hadith tie the start and end of Ramadan to seeing the crescent, and say to complete 30 days if it is hidden by cloud.
• Local sighting holds that each region follows its own sighting; another view accepts a reliable sighting from anywhere.
• Calculation-based bodies, such as the Fiqh Council of North America and Turkey's Diyanet, publish dates in advance using stated astronomical criteria.
• Saudi Arabia's Umm al-Qura calendar is calculated for civil use, while the start of Ramadan there is confirmed from sighting reports.
• In February 2026 these approaches put the first day of Ramadan on two different days, a day apart.

What the Quran and hadith say

The texts behind the debate are short, and everyone in it quotes the same ones.

The Quran sets the fast of Ramadan in Surah al-Baqarah 2:185. The key phrase is faman shahida minkum al-shahr. Saheeh International, on quran.com, translates its meaning as "whoever sights [the crescent of] the month." The bracketed words are the translators' addition. M.A.S. Abdel Haleem's translation on the same site gives "any one of you who is present that month." The two translations already show that the wording can be read in more than one way.

The hadith are more specific. In Sahih al-Bukhari 1906, the Prophet ﷺ said not to fast until the crescent is seen and not to stop until it is seen again, "but if the sky is overcast... then act on estimation." The Arabic for that last instruction is faqdurū lahu. In Sahih al-Bukhari 1909, the instruction for an overcast sky is to complete thirty days of Sha'ban.

A third narration, Sahih al-Bukhari 1913, is central to the calculation question. The Prophet ﷺ said, "We are an illiterate nation; we neither write, nor know accounts," and that the month is sometimes 29 days and sometimes 30.

How these texts apply today is where scholars differ:

• Scholars who require sighting read 1909 as explaining 1906: "estimation" means counting 30 days, and the command is tied to seeing. The AMJA fatwa discussed below takes this line.
• Scholars who accept calculation hold that a physical sighting is not strictly required once the start of the month can be established by precise calculation, the position stated on the Fiqh Council of North America's calendar page.

This article sets out the positions; it does not decide between them. Personal decisions belong with qualified scholars and your local mosque.

Position 1: local sighting

Under local sighting, a month begins when the crescent is seen in your own region, or after 30 days if it is not. A sighting in a distant country does not by itself start the month for you. Jurists call this taking account of ikhtilaf al-matali', the difference of horizons.

The main textual support is the report of Kuraib in Sahih Muslim 1087. Kuraib saw the Ramadan crescent in Syria on Friday night. Back in Madinah, he told Ibn 'Abbas, who said it had been seen there on Saturday night. Ibn 'Abbas said they would keep counting by their own sighting. Asked whether Mu'awiya's sighting was enough, he said it was not: "this is how the Messenger of Allah (ﷺ) has commanded us." The chapter heading on sunnah.com summarises the point: each land has its own sighting.

National committees that search for the crescent work this way. On the evening of 17 February 2026, for example, Algeria's national crescent-observation commission at the Ministry of Religious Affairs announced that Ramadan 1447 would begin on Thursday 19 February because the crescent could not be sighted in various regions that evening.

The strength of this approach is that it keeps close to the wording of the hadith. Its practical cost is that the start date is not known until the evening before, and neighbouring countries can differ.

Position 2: a sighting anywhere

The second view also requires an actual sighting, but does not limit it to a region. If the crescent is reliably seen anywhere, or in a recognised Muslim authority's territory, that sighting is accepted more widely. This is sometimes called ittihad al-matali', unity of horizons.

The Assembly of Muslim Jurists of America (AMJA) states this position in its 2013 fatwa on astronomical calculations. AMJA treats physical sighting as the basis, describes relying on calculation in place of sighting as "a newly invented thing," and says that when a sighting is confirmed in an Islamic country, Muslim communities outside the Muslim world "will abide by it." It also says it has not adopted the view of separate sighting zones.

In practice, many communities that follow this view take the announcement of Saudi Arabia or another country. The difference between this position and local sighting has its own article: global vs local moon sighting.

Position 3: calculation-based calendars

Calculation-based calendars decide each month in advance by a published rule. They differ in what that rule is and in what they are for.

The Fiqh Council of North America

The Fiqh Council of North America (FCNA) "recognizes astronomical calculation as an acceptable Shar'i method for determining the beginning of Lunar months," according to its Ramadan and Shawwal 1447 announcement. Its calendar page states the criteria: after conjunction somewhere on the globe, at local sunset, the angle between the Sun and Moon must be at least 8° and the Moon at least 5° above the horizon. If the conditions are met, the new month begins the next day; if not, the day after. The page states that a physical sighting "is not necessary." For Eid al-Adha, FCNA follows the Day of Arafah as determined in Saudi Arabia. Its Ramadan announcement adds that these 8° and 5° criteria are the ones it has historically used from the European Council for Fatwa and Research (ECFR).

Turkey's Diyanet and the 2016 Istanbul congress

The Presidency of Religious Affairs of Türkiye (Diyanet) follows the International Hijri Calendar Union Congress held in Istanbul in May 2016. The congress's final declaration (in Arabic) chose a single calendar for the whole world, based on the possibility of sighting anywhere and without regard to differences of horizon.

The core test uses the same 8° elongation and 5° altitude thresholds as FCNA, but with a fixed cut-off in Greenwich time. A study by Yunus Keleş in the Turkish journal İslam Hukuku Araştırmaları Dergisi (2016, in Turkish) describes Diyanet's practice: if the crescent becomes visible somewhere before midnight Greenwich time, the following day is the first of the month; if only after midnight, the month starts a day later.

The Diyanet Center of America's Ramadan 1447 statement also lists two conditions for a sighting to count. The conjunction must come before dawn (imsak) in New Zealand, the world's easternmost point. And the crescent must be seen over the main landmasses of North and South America. The statement says that once the criteria are met, seeing the crescent and confirming by calculation that it is visible count the same.

Saudi Arabia's Umm al-Qura calendar

The Umm al-Qura calendar is also calculated, but with a simpler rule and a different purpose. Since 1423 AH, a month ends after 29 days only if, on the 29th at Makkah, the conjunction happens before sunset and the Moon sets after the Sun, as R.H. van Gent of Utrecht University sets out on his page on the astronomical rules of the Umm al-Qura calendar. He describes it as used by the Saudi government "for civil purposes." For Ramadan, the start is confirmed by Saudi Arabia's Supreme Court from sighting reports, as the example below shows. The full rules and their history are in the Umm al-Qura calendar explained.

Why calculation is not the same as predicting a sighting

Calculation can give the instant of the new moon. The US Naval Observatory's crescent visibility page says the date and time of each new moon "can be computed exactly," but that first sighting of the crescent "cannot be predicted with certainty," because it depends on sky conditions and the observer's location, experience and preparation. Each calculation-based calendar therefore chooses a threshold. A rule like Umm al-Qura's checks only that the Moon is above the horizon at sunset; the 8° and 5° rule aims closer to likely visibility. How astronomers model visibility is covered in crescent visibility criteria.

The positions side by side

A worked example: Ramadan 1447 (February 2026)

The new moon before Ramadan 1447 fell on Tuesday 17 February 2026 at 12:01 UT, according to the US Naval Observatory's moon phase data. That evening was 29 Sha'ban 1447 in the calculated Umm al-Qura calendar.

For Makkah on that day, USNO's sun and moon data for one day give sunset at 18:19 and moonset at 18:23 (UTC+3). The conjunction (15:01 Makkah time) came before sunset, and the Moon set four minutes after the Sun, so both Umm al-Qura conditions were met and the calculated calendar made Wednesday 18 February 1 Ramadan. The Moon was only about three hours past conjunction at that sunset.

The different approaches came out as follows:

Two details stand out. FCNA's own announcement acknowledged that "sighting is not possible on February 17" and described keeping its long-standing method as "a judgment call rather than a technical one." And Diyanet and FCNA, which share the 8° and 5° thresholds, still arrived at different days. By Diyanet's calculation the crescent first became visible at 03:42 GMT, after the Greenwich midnight cut-off and beginning from the Pacific region, so the month started a day later. FCNA's rule instead looks at local sunset on 17 February somewhere on the globe. The difference between communities was not simply "sighting vs calculation"; it also came from which sighting, and which calculation rule.

Ramadan 1448 (February 2027) in the calculated calendars

For 1448 AH, FCNA's published calendar matches the calculated Umm al-Qura dates for all twelve months. FCNA's Dhu al-Hijjah date is provisional, since it follows the Day of Arafah as determined in Saudi Arabia. Both put 1 Ramadan 1448 on Monday 8 February 2027. USNO gives the preceding new moon as 6 February 2027 at 15:56 UT, which is 18:56 in Makkah, after that day's 18:13 sunset there. So on 29 Sha'ban the Umm al-Qura condition fails, and Sha'ban runs to 30 days. In the calculated calendar the first night of Ramadan is Sunday 7 February, and the first fast is Monday 8 February.

That agreement is a property of the 1448 dates, not of the methods. Communities that wait for a sighting will make their own announcements on the evening of their 29 Sha'ban, and those can differ by a day.

What to do next

• Follow the method your local mosque or national authority uses, and ask a qualified scholar if you need to choose between them.
• Use calculated dates for planning, and mark them as provisional until your announcement. The Ramadan dates page shows the calculated start and end.
• Check today's calculated Hijri date on the calendar home page, and see where the Moon is in its cycle on the moon phases page.
• If your app shows a different date from your mosque, a guide on our sister site Everyday Muslim, using a Hijri calendar alongside local announcements, explains how to keep the two straight.