in category Fiqh (Jurisprudence)

Did classical scholars permit calculations as a means to determine the new moon?

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Islamic researcher, graduated from Al-Azhar University, Islamic Studies in the English language. I also studied at Temple University in the US.
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In a Nutshell:
A minority opinion historically permitted calculations - only when cloudy after attempting to sight the new moon. This view was rejected by majority of classical scholars who argued for sighting and completing Sha'ban in the absence of a moonsighting. Explicit ahadith narrate the Prophet (saw) stating what to do when the moon cannot be sighted. Some contemporary Muslims not only adopt this weak opinion but demand the abandonment of sighting for calculations.


During the 1990s, some Muslim organisations began raising arguments for the use of calculations. Many Muslim scholars and jurists refuted their arguments at the time, in particular, their misrepresentation of a minority opinion that only permitted calculations if it was cloudy whereby the moon could not be sighted or for personal use rather than communal use.

Such calculation arguments are reappearing after a long absence.

Juristic Analysis

Classical scholars historically reached a consensus that required the moon be sighted by the eye.

Ibn Taymiyyah in majm'u al fatwa (132/25) wrote:

قال ابن تيمية في مجموع الفتاوى (25 / 132):” فإنا نعلم بالاضطرار من دين الإسلام أن العمل في رؤية هلال الصوم أو الحج أو العدة أو الإيلاء أو غير ذلك من الأحكام المعلقة بالهلال بخبر الحاسب أنه يرى أو لا يرى لا يجوز . والنصوص المستفيضة عن النبي صلى الله عليه وسلم بذلك كثيرة . وقد أجمع المسلمون عليه.
"We know (due to necessity) that from the deen of Islam to act upon the moonsighting for Ramadan, hajj, counting the i'ddah (waiting period), ila (divorce) or other rulings which are based upon sighting the Crescent based upon the news of one who calculates claiming they have sighted or haven't is invalid. The texts which have been narrated from the prophet concerning this are multiple and indeed the Muslims are unanimously agreed upon this".

Whilst Ibn Hajr al-Asqalani in fath al-bari (127/4) observed:

وقال ابن حجر في فتح الباري (4 / 127):” وقد ذهب قوم إلى الرجوع إلى أهل التسيير في ذلك وهم الروافض، ونقل عن بعض الفقهاء موافقتهم. قال الباجي: وإجماع السلف الصالح حجة عليهم “.

"Some scholars stated that this concept (astronomical calculations) goes back to ahl at-tasyeer who were from the rawafidh and it was narrated that some of the fuqaha agreed with them however, the consensus of the salaf as-salah is a proof against them".

A minority opinion permitted calculations if and only if it was cloudy or for personal use however they required the sighting be undertaken first. Their views were based on the hadith narrated by ibn Umar (ra):

ذَكَرَ رَمَضَانَ فَضَرَبَ بِيَدَيْهِ فَقَالَ ‏ "‏ الشَّهْرُ هَكَذَا وَهَكَذَا وَهَكَذَا - ثُمَّ عَقَدَ إِبْهَامَهُ فِي الثَّالِثَةِ - فَصُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ فَإِنْ أُغْمِيَ عَلَيْكُمْ فَاقْدِرُوا لَهُ ثَلاَثِينَ ‏"
Allah's Messenger (saw) as saying in connection with Ramadan, "the month is thus and thus. (He then withdrew his thumb at the third time). He then said: "Do not fast till you see the new moon, and do not break fast till you see it; but if the weather is cloudy calculate about it." (Sahih Muslim 2364)

Did classical scholars permit calculations as a means to determine the new moon?
The latter group understood the final part of the hadith as saying if one couldn't sight the moon after trying to look for it, then calculations could be used.

The term فَاقْدِرُوا (calculate) mentioned in this hadith is unclear as to what it refers to - which allowed some to argue it could include astronomical calculations based on astronomical data.

The vast majority of scholars however rejected this opinion, some in very harsh terms, because "calculate" mentioned in the hadith must be understood through the shawahid (similar narrations) of the same hadith that explain the term and indicate if the narrator omitted any words - narrators often summarised or focusing on certain aspects of what was being narrated.

In the Tafseer of Imam Al-Qurtabi, Ibn Nafi'i (ra) reported Imam Malik bin Anas (ra) said:

"If you see an Imam who does not begin and end fasting by way of sighting, but begins fasting by calculation, he should not be followed in prayer or emulated."

The renowned scholar Ibn Al-Arabi said:

"Some of our people erred when they reported that Imam Shafi'i relied on calculations... The report is baseless and false."

Only two ambiguous shawahid (Muslim and Nisa'i 2120) included an unclear term فَاقْدُرُوا (calculate) - this term must be understood in light of other shawahid in Muslim and Nasa'i that refer to the completion of the month of Sha'ban.

This hadith has numerous shawahid in Bukhari 1909 and Muslim 2379, 2380, Nisa'i 2118, 2119, 2120, 2126, 2129, 2191 Tirmidhi 684, 688 and others.

For example, the narrations of Abu Huraira clarify what was meant by "calculate", namely completion of 30 days:

فَإِنْ غُمِّيَ عَلَيْكُمُ الشَّهْرُ فَعُدُّوا ثَلاَثِينَ

"Whenever you sight the new moon (of Ramadan) fast, and when you sight it (the new moon of Shawwal) break it, and if the sky is cloudy for you, then fast for thirty days." (Sahih Muslim 2379)

The narration of Nisa'i on the authority of ibn Abbas (ra) adds more details:

فَإِنْ حَالَ بَيْنَكُمْ وَبَيْنَهُ سَحَابَةٌ أَوْ ظُلْمَةٌ فَأَكْمِلُوا الْعِدَّةَ عِدَّةَ شَعْبَانَ وَلاَ تَسْتَقْبِلُوا الشَّهْرَ اسْتِقْبَالاً وَلاَ تَصِلُوا رَمَضَانَ بِيَوْمٍ مِنْ شَعْبَانَ ‏"
"If clouds or darkness prevent you from seeing it, then complete the number of days of Sha'ban, and do not fast ahead of the month, and do not join Ramadan to a day of Shaban." (Nisa'i 2191)

The narration of Abu Huraira in Bukhari also clarifies what the Prophet meant:

فَإِنْ غُبِّيَ عَلَيْكُمْ فَأَكْمِلُوا عِدَّةَ شَعْبَانَ ثَلاَثِينَ
"If the sky is overcast (and you cannot see it), complete thirty days of Sha'ban." (Bukhari 1909)

The vast majority of scholars thus understood the wording "to calculate if the sky was cloudy" as referring to counting thirty days - not astronomical calculations and predictions.

Scholars who Permitted Astronomical Calculations:

Those who permitted calculations on cloudy days did so because some argued the former ahadith is not necessarily explained by the latter hadith, i.e., the calculate has not been explained by the hadith about calculating the thirty days but rather they refer to two different groups. The claim is the former hadith is referring to astronomers and mathematicians and the latter refers to the laity. However, some scholars condemned this explanation as absurd - the prophet never referred anything to astronomers and mathematicians.

These scholars sought to their opinions in hadith without going beyond it. None abandoned the sighting as the cause (sabab) of Ramadan or eid nor replacing sighting altogether.

The Maliki jurist Ibn Rushd states in al-Muqadimaat:

ولَا يَجِبُ صِيامُ شَهرِ رَمَضَانَ إلا بِرُؤيَةِ الهِلَالِ أو إِكْمَال شعبانَ ثَلاثِينَ يَومًا،... أهلُ العِلِمِ اختَلَفُوا في مَعْنَى قَولِ النبيِ - صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ - فَاقْدِرُوا لَهُ، فَرُوِيّ عنْ ابنِ عُمَرَ أنّهُ كان إِذَا كَانَت السَمَاء صاحِيّة أَصْبَحَ مُفْطِرًا، وإِنْ كان مُغَيِمَةً أَصْبَحَ صَائِمًا، ... وقَدْ قِيِلَ: إنّ مَعْنَى قَوْلِهِ فَاقْدِرُوا لهُ مِنَ التَقْدِيرِ، أن يُقْدَرَ لِمَنَازِلَ القَمَر وطَرِيقَ الحِسَاب.
فَرُوِيّ عن مُطْرِف بن عبدِ اللهِ بن الشِخِير أنه كان يقول يُعْتَبَرُ الهِلالَ إذا غُمَّ بالنُجُومِ ومَنَازِلَ القَمَرِ وطَرِيق الحِسَابِ. ورُوُيّ مِثْلُ ذلك عن الشَافِعِي - رَضِيَ اللَّهُ تَعَالَى عَنْهُ - في روايةٍ. والمَعْرُوفُ لَه المَشْهُور ُعَنْهُ أنهُ لا يُصَامُ إلا بِرُؤيَّةٍ فَاشِيّةٍ أو شَهَادَةٍ عَادِلةٍ كالذي عليه الجُمْهُور. والصَوَابُ ما ذَهَبَ إليهِ مالكٌ... لأنَّ التقدِيرَ يكونُ بمَعْنَى التَمَام.
"It is not wajib to fast the month of Ramadan except by seeing the hilal (the beginning part of moon) or by completing the month of Sha'ban thrity days... (the above narrations).
Scholars disagree on the meaning of the Prophet's statement 'calculate it.'
Ibn Umar is quoted (meaning) fasting and breaking the fast according to the light of the moon and if there are clouds, do not fast. Others argued it means the stages of moon should be calculated.
It was narrated the (first-century tabi'i) Mutarrif bin al-Shikhir used to say, 'The hilal is known when it is hidden through stars and the stages of the moon and the matter of the calculation. (It is wrongly attributed "personally and privately" to ibn Rushd: al-Hattab, Mawahib al-Jaleel, Vol. 2, p. 388).'
A similar notion was attributed to Shafi'i by only one narration (of his student Surayjj), but the contrary is known and widespread that he argues there is no fasting except by a clear vision (public) vision if the moon, or a trustworthy testimony. It is similar to the opinion of the jumhur (majority of scholars).
The valid view is the view of Malik ... because the calculation (taqdeer in the hadith) means the completion (of the month). (Ibn Rushd, al-Muqadimaat al-Mumahadat, Vol. 1, p. 250)

The same view was also adopted by the third-century muhadith ibn Qutaybah. (al-Ayni, Umdat al-Qari, Vol. 10, p. 261) But ibn Qutaybah's view did not receive much weight because he is not a jurist, rather a hadith scholar. The other two narrations of Mutarrif and Surayjj are considered inauthentic by the fourth-century jurist ibn Abd al-Bar. (Ibn Hajar, Fath al-Bari, Vol. 1, p. 122)

But some Hanafi scholars permitted it in a very limited and necessary context. (al-Ayni, Umdat al-Qari, Vol. 10, p. 271, Rasa'il ibn Abdeen, Vol. 1, p. 224)

Scholars who Prohibited Astronomical Calculations:

These are the majority of scholars (Malik, Shafi'i, Abu Hanifah and others) and their view is supported by the discussion of the shawahid above as the Prophet identified two ways: the visual realisation or the counting of thirty days of Sha'ban in times of ambiguity. But Ahmed ibn Hanbal argued the term qadiru in the hadith means to make Sha'ban 29 days, but the latter view contradicts the linguistic and hadith analysis of this term.

Al-WazIir bin Hubayrah (d. 560 AH), who was an Iraqi Arab official and jurist, argued the position of the four sunni scholars:

وَلم يقل: صُومُوا لِلْحسابِ وَافْطرُوا لَهُ.
وَاتَّفَقُوا على أَن ذَلِك إِنَّمَا يجب من رُؤْيَة أَو إِكْمَال عدد أَو وجود عِلّة.
"The Prophet (saw) did not say: 'fast and break the fast based on calculation.' (contrary to the terms of hadiths above)
(The four schools agreed) agreed it is only wajib through seeing the moon or completing the number (thirty days) or the existence of a illah (cause). (Al-WazIir bin Hubayrah, Ikhtilaf al-A'imah al-Ulama, Vol. 1, p. 234)

The eighth-century Shafi'i jurist Imam Subki is sometimes cited to justify calculations, however, he claimed an ijma in not using astronomical calculations to determinate a new moon, ikhtilaf only where it is cloudy and calculations predict it would normally be seen.

He argued when he mentioned the issue of astronomical calculations as a valid strategy:

وَهَذَا بَاطِلٌ فِي الشَّرْعِ قَطْعًا لَا اعْتِبَارَ بِهِ
"This is batil (invalid) in shari'ah for certain and it is not considered." (Fatawa as-Subki, Vol. 1, p. 280)

He then argued the same argument classical scholars above and added:

وَهَذَا مَحَلٌّ مُجْمَعٌ عَلَيْهِ لَا خِلَافَ فِيهِ بَيْنَ الْعُلَمَاءِ، وَثَمَّ مَحَلٌّ آخَرُ اخْتَلَفُوا فِيهِ ... وَهُوَ مَا إذَا دَلَّ الْحِسَابُ عَلَى أَنَّهُ فَارَقَ الشُّعَاعَ وَمَضَتْ عَلَيْهِ مُدَّةٌ يُمْكِنُ أَنْ يُرَى فِيهَا عِنْدَ الْغُرُوبِ فَقَدْ اخْتَلَفَ الْعُلَمَاءُ فِي جَوَازِ الصَّوْمِ بِذَلِكَ وَفِي وُجُوبِهِ
"This is the consensus of scholars. But what scholars have disagreed upon ... (meaning) is the situation when the calculation proves the beginning of the month and it lasted for a while that angle of elongation is such that visibility is seeable.
Scholars disagree on whether it is permissible (ja'iz) or mandatory (wajib ) to fast accordingly." (Ibid)

He then discussed the above ahadith and argued the majority's opinion is the correct one:

وَهَذَا هُوَ الْأَصَحُّ عِنْدَ الْعُلَمَاءِ
"This is the correct view according to scholars." (Ibid, Vol. 1, p. 281)

The seventh-century Shafi'i-Maliki jurist Ibn Daqiq al-Id is also quoted in support of calculations explains his stance in Ihkam al-Ihkam:

إنَّ الْحِسَابَ لَا يَجُوزُ أَنْ يُعْتَمَدَ عَلَيْهِ فِي الصَّوْمِ، لِمُفَارَقَةِ الْقَمَرِ لِلشَّمْسِ، عَلَى مَا يَرَاهُ الْمُنَجِّمُونَ، مِنْ تَقَدُّمِ الشَّهْرِ بِالْحِسَابِ عَلَى الشَّهْرِ بِالرُّؤْيَةِ بِيَوْمٍ أَوْ يَوْمَيْنِ. فَإِنَّ ذَلِكَ إحْدَاثٌ لِسَبَبٍ لَمْ يُشَرِّعْهُ اللَّهُ تَعَالَى. وَأَمَّا إذَا دَلَّ الْحِسَابُ عَلَى أَنَّ الْهِلَالَ قَدْ طَلَعَ مِنْ الْأُفُقِ عَلَى وَجْهٍ يُرَى، لَوْلَا وُجُودُ الْمَانِعِ - كَالْغَيْمِ مِثْلًا فَهَذَا يَقْتَضِي الْوُجُوبَ، لِوُجُودِ السَّبَبِ الشَّرْعِيِّ.
"My position is as follows: calculation is not permissible for fasting by determining the separation point of the conjunction of the sun and moon based upon the position of the astronomers who see the start of the new month as something that precedes the actual sighting (of the crescent) by a day or two.
That is in fact innovating a legal cause (sabab) that God has not legislated.
But when the ability to calculate determine that the visibility curve of the crescent is such that it would be seen had not something preventing its visibility caused that, such as clouds, then, in such a case, the obligation to fast is necessary because the legal cause for the fast is there." (Ibn Daqiq, Ihkam al-Ihkam, Vol. 2, p. 8)

He considered it a reprehensible innovation to replace the sighting with calculations and only permitted calculations if the sky was cloudy on the 29th day. He also gives another example of a man in a dungeon and cannot see the moon but knows through calculations it is Ramadan, he states in this situation it's an obligation for him to fast.

None of the scholars who followed this minority opinion of permitting calculations did so through abandoning the sighting method but did so if the sky was cloudy and only on the calculation of the prediction of the visibility of the crescent and not on the birth of the new moon. This minority opinion is not a stated opinion of any of the main schools of thought - aside from a late Shafi'i opinion which is discussed in the next section.

Qadi Abu Bakr Ibn al-Arabi's response in his book Aridat al-Ahwadhi bi Sharh Sahih al-Tirmidhi said:

قولِهِ صُومُوا لرُؤيَتِهِ، تَحْقِيقٌ واضِحٌ في ذَلِكَ المَعْنَى أيضًا ونَصٌ في أنْ لا يَتَعَدَى رُؤْيّةُ الهِلَالِ في الفِطْر ِوالصَومِ لأنَّ مِعْيّارِ العِبَاداتِ الذي به يَتَحَقَقُ مِقْدَار الفُرُوض. ...
ِارْبِطُوا عِبَادَتُكُم بِرؤيَتِهِ واجْعَلُوا عِبَادَتُكُم مُرْتًبِطَةً ابتِدَاءً وانتِهَاءً باستِهْلِالِه ...
بعضُ الشافِعِيةِ يقولُ أنّهُ يُرَّجِحُ في اسْتِهْلَال الهِلالَ إلى حِسَابِ المُنَجِمِين ... وهذه هفوةٌ لا مَرَّدَ لَهَا ...
ِأُوه ابن شريح؛ أينّ مُسالتُك الشَرِيحِيّة ... تَسْلُكُ هذا المَضِيقَ في غيرِ الطريقِ وتَخْرُجُ إلى الجَهْلِ عَنْ العِلْم
والتَحْقِيق: ما لمُحَمَدٍ والنُجُوم
"The hadith, "Fast when the crescent is sighted and break the fast when it is sighted," is explicitly unambiguous and a decisive text (nass) clearly meaning that one cannot bypass sighting the moon in either fasting or ending the fast. The reason is that [sighting] is the criterion given for the obligation and its determined length...

(The Prophet (s) is telling us) to bind worship to physical sighting—to make your worship connected in its outset and its end with the appearance of the crescent....

(Concerning the end of the hadith, "if the crescent is obscured,") I have seen some Shafi'i scholars claim that to determine its birth, one can resort to calculations of astronomers... This is a mistake that cannot be fixed, a slip from which there is no recovery, a distancing from which no nearness can come after, a humiliation that cannot find redemption. O Ibn Surayj! Where is your famous Surayjiyyah? You follow this narrow rough path off the road. Tell me, what does Muhammad (s) have anything to do with stars?" (Aridat al-Ahwadhi bi Sharh Sahih al-Tirmidhi, Vol. 3, pp. 204-8)

As regards claims that this was Imam Shafi'i's opinion, Ibn Abd al-Barr in his book al-Istidhkar states the attribution to Shafi'i is not valid:

قَالَ أَبُو عُمَرَ الَّذِي عِنْدَنَا فِي كُتُبِهِ أَنَّهُ لَا يَصِحُّ اعْتِقَادُ رَمَضَانَ إِلَّا بِرُؤْيَةٍ فَاشِيَةٍ أَوْ شَهَادَةٍ عَادِلَةٍ أَوْ إِكْمَالِ شَعْبَانَ ثَلَاثِينَ يَوْمًا...
وَعَلَى هَذَا مَذْهَبُ جُمْهُورِ فُقَهَاءِ الْأَمْصَارِ بِالْحِجَازِ وَالْعِرَاقِ وَالشَّامِ وَالْمَغْرِبِ مِنْهُمْ مَالِكٌ وَالشَّافِعِيُّ وَالْأَوْزَاعِيُّ وَأَبُو حَنِيفَةَ وَأَصْحَابُهُ وَعَامَّةُ أَهْلِ الْحَدِيثِ إِلَّا أَحْمَدَ بْنَ حَنْبَلٍ وَمَنْ قَالَ مِنْهُمْ بِقَوْلِهِ
"However, Abu Amr said 'what we have found authenticated in his own books is that he considered the month of Ramadan to be valid only by a widespread sighting or sound testimony or completion of thirty days of Shaban... This is in fact the school of all of the scholars of the Hijaz, Iraq, Greater Syria, and the West. Among those who confer are Malik, al-Shafi'i, al-Awzai, Abu hanifah and his students, and all of the people of hadith, except for Ahmad bin Hanbal and those who conferred with him." (Ibn Abd al-Bar, al-Istidhkar, Vol. 3, p. 278)

So the authenticated view of Imam Shafi'i according to ibn Abd al-Barr is that he didn't permit calculations on a cloudy night. Since Imam al-Nawawi's time, the Shafi'i school has been increasingly accepting of the personal use of calculations for fasting. Subki (ra) is usually accredited for this shift, some argue al-Nawawi himself started this trend. Whilst a small number of earlier Shafi'i scholars accepted it, it has always been a small minority.

The opinion was accepted by both Zakariya al-Ansari and al-Ramli, though not by Imam Ibn Hajar (ra). These imams formed the basis for reliable opinions in the late Shafi'i school.

For similar views, see:

  • Siniki, Asna al-Mattalib, Vol. 5, p. 269;
  • Siniki, Sharh al-Bahjah, Vol. 7, p. 15;
  • Ramli, Nihayat al-Muhtaj, Vol. 9, p. 293;
  • Al-Bayjuri, Hashiyat al-Bayjuri, Vol. 2, p. 181.

I mentioned above Ahmad bin Hanbal's opinion was with little difference with the majority view. The Day of Doubt is prohibited to be fasted according to majority of scholars, but ibn Hanbal argued it should be guaranteed because it may be a day of Ramadan. So the last day of Sha'ban should be fasted as a way of insurance.

Ibn Abd al-Bar narrated his position:

"Ahmed ibn Hanbal said fasting in the day of doubt is wajib and it is counted as Ramadan day if it's been proven (later) it is from Ramadan." (Ibn Abd al-Bar, al-Istidhkar, Vol. 3, p. 277)


A minority opinion historically permitted calculations only on a cloudy night after attempting to sight the new moon. This view however was rejected by the majority of classical scholarship who relied on sighting and completing the month of Sha'ban in the absence of sighting the moon. This opinion was extracted from very explicit ahadith as the Prophet (saw) told us what to do in the times of ambiguity and unambiguity. Some Muslims not only adopt this weak opinion but demand the abandoning of sighting to be replaced with calculations.

Calculating the potential visibility of a crescent is not a definite exercise as it is a non-predictable phenomenon, the potential visibility affected by numerous factors like the angle of elongation, the atmospheric pressure, the humidity in the atmosphere, illuminicity at twilight and even wind direction. Once can't predict all of these variables which is why some want to even change the fact that it's no longer about the hilal and but the astronomical new moon.

Main References

Ibn Rushd, al-Muqadimaat al-Mumahadat
Al-Ayni, Umdat al-Qari
Ibn Hajar, Fath al-Bari
Rasa'il ibn Abdeen
Al-WazIir bin Hubayrah, Ikhtilaf al-A'imah al-Ulama
Fatawa as-Subki
Ibn Daqiq, Ihkam al-Ihkam
Ibn al-Arabi, Aridat al-Ahwadhi bi Sharh Sahih al-Tirmidhi
Ibn Abd al-Bar, al-Istidhkar.

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