Should Ramadan begin by local moon sighting or by calculation?

The two positions

Where the disagreement actually lies

The dispute is not about whether calculation is accurate. It is about what the word "sighting" in the texts means, and about a single phrase in one narration.

The command is repeated in several wordings: fast when you see the crescent, break the fast when you see it, and if it is obscured from you, complete the count at thirty. The Hanbalis and the majority read "see" as seeing with the eye — a physical act, not knowledge or probability. Ibn Baz makes the grammatical point that the verb here takes a single object, which marks it as sight rather than knowing, and adds that the Companions understood it that way, and they knew the language and the intent of the law better than anyone after them.

The minority position rests on one narration in which the Prophet ﷺ said, when the sky is overcast, "then measure it." They took "measure" to mean calculate. The majority answer that other narrations of the same hadith explain it: "then measure it as thirty," and "complete the count of Sha'ban at thirty." On that reading the instruction is to finish the month by number, not to turn to astronomy. Ibn Baz notes that the minority applied calculation in clear skies as well, while the narration ties the alternative to cloud — so their reading does not fit the text they cite.

There is a second, practical argument the scholars give. Sighting is something almost anyone can do, in desert or city, scholar or ordinary Muslim. Calculation is known only to a few, and may be settled in one time or place and not another. Tying an act of worship to something the whole community cannot reach would create the hardship the law avoids.

Calculation as a condition on sighting

A distinct claim is that a sighting is only valid if the astronomers confirm the crescent was born or could be seen. Ibn Baz rejects this sharply: the Prophet ﷺ knew that astronomers would later disagree with trustworthy witnesses, and he still did not make their verdict a condition. To add such a condition, he says, is to legislate a requirement with no basis in the revealed law.

What is permitted

The prohibition is on relying on calculation, not on using instruments. Ibn Uthaymeen states that using a telescope to sight the crescent is permissible though not required, and that if a trustworthy person sees it through one, that sighting is acted upon. The same principle appears in the decision of the Saudi Council of Senior Scholars and in the statement of the Islamic Fiqh Council: sighting through observatories is a real sighting, whether with the naked eye or with an instrument. What is rejected is treating the observatory's data as the standard the sighting must match.

Where they agree

The points the scholars treat as settled are worth separating from the disputed ones:

• The month is entered only by sighting or by completing Sha'ban at thirty. This is reported as the position of all the scholars, and Ibn Taymiyyah is quoted as saying there is consensus that calculation is not used to establish the crescents.
• The month may be twenty-nine or thirty days. This is not disputed.
• If the crescent is sighted, fasting is obligatory. This too is agreed.
• A single upright witness suffices to begin Ramadan, while two are required to end it and for the other months. Ibn Baz attributes the single witness for entry to the majority, citing the report of Ibn Umar رضي الله عنه and the bedouin who testified before the Prophet ﷺ.

What this means for you

If you live where the crescent is sighted and announced, you fast and break the fast with the community. If the sky is overcast and no sighting is confirmed, you complete Sha'ban at thirty and then fast — you do not begin a day early on the strength of a calendar.

If you live where the authorities establish the month by calculation alone, the guidance is not to follow them in that. IslamWeb sets out the order to follow: sight the crescent yourselves; if you cannot, fast with the nearest Muslim land that does sight; if that is not possible either, then with a body that does not rely on calculation. What is described as an innovation is each person fasting with his own home country, which multiplies the confusion rather than resolving it.

One practical consequence IslamWeb notes: if you fasted twenty-nine days on calculation and the true month was thirty, you make up a day; if you fasted on calculation and it turned out you had fasted on the day of Eid, you make that day up as well.

Key takeaways

• Ramadan is established by sighting the crescent or by completing Sha'ban at thirty days — not by astronomical calculation.
• The disagreement is over what "sighting" means and how one narration is read, not over the accuracy of astronomy.
• Using a telescope to sight is permitted; making the observatory's data a condition on the sighting is not.
• A single upright witness begins Ramadan; two are needed to end it.
• If you cannot sight and have no reliable body to follow, fast with the nearest land that sights rather than with a calculation-based calendar.

Further reading

• Ibn Baz, Majmu' Fatawa wa Maqalat, "Dukhul al-Shahr wa Khurujuh"
• al-Nawawi, al-Majmu'
• Ibn Taymiyyah, Majmu' al-Fatawa

And Allah knows best.