Moon Sighting or Calculation: Why Ramadan Dates Differ
Every year the same scene repeats: one country starts Ramadan on Monday and another on Tuesday, and some people celebrate Eid a day before their neighbours. This is not necessarily an error of calculation; it results from different methods and different observers' positions. Understanding it takes away the confusion and helps you plan.
Why is the crescent not seen everywhere on the same night?
At conjunction (the astronomical birth of the new moon) the Moon lies between the Earth and the Sun and cannot be seen. It then moves away from the Sun and appears after sunset as a thin sliver. For the crescent to be visible, enough time must pass after conjunction, the Moon must be far enough from the Sun, it must set long enough after the Sun to be told apart on the western horizon, and the sky must be clear. Because the Earth turns, sunset reaches the west after the east, by which time the Moon has moved further; the crescent may therefore be seen in a western country and not in an eastern one on the same night. This is the difference of horizons.
The sighting method
Many countries, Morocco among them, observe the crescent after sunset on the evening of the 29th, following the Prophet's ﷺ words: "Fast when you see it and break the fast when you see it; if it is hidden from you, complete the month of Sha'ban as thirty days" (agreed upon). If the crescent is seen, the new month starts the next day; if not, the current month is completed at thirty days. The announcement is made by an official body after observation committees report; in Morocco, the Ministry of Habous and Islamic Affairs announces it.
The calculation method
Other bodies rely on astronomical calculation, which fixes the time of conjunction and the Moon's position precisely and allows calendars to be published years ahead. Calculation itself comes in several forms: some require only that conjunction precede sunset, others add conditions on the Moon setting after the Sun or on its altitude and elongation, and some tie the result to Mecca alone while others treat each country separately. Hence there are differences among calculated calendars too, not only between calculation and sighting. Umm al-Qura uses one standard on Mecca time (we explained its two conditions in What Is the Hijri Calendar and How Is It Calculated?).
Examples that show the difference
By Umm al-Qura, 1 Ramadan 1448 AH is Monday 8 February 2027, Eid al-Fitr is Tuesday 9 March 2027 and Eid al-Adha is Sunday 16 May 2027. If your country relies on sighting and the crescent is not seen on the evening of Sunday 7 February, Sha'ban will be completed at thirty days and Ramadan will begin on Tuesday 9 February. This is an illustration of the mechanism, not a forecast of any country's announcement; the real announcement comes only on the evening in question.
A practical rule: the gap between calculation and sighting is usually one day, not more, and a calculated calendar either matches a sighting-based announcement or comes before it, rarely after.
A teaching scenario: the 29th of Sha'ban
Here is what happens in a country that uses sighting. It is a simplified teaching example, not a description of any particular country's procedure.
- The month reaches the evening of the 29th, and observation committees go to places with an open western horizon before sunset.
- After sunset observers look for the crescent during a short window; if the sky is cloudy or the Moon is too close to the Sun, it is not seen.
- Testimonies are gathered and reviewed, and the official body usually announces the result the same night.
- If sighting is confirmed, the next day is the first of the month; if not, the next day is the thirtieth of the current month.
This is why no website can state in advance with certainty when Ramadan begins in a sighting country; the most it can say is "expected by calculation".
When do calculation and sighting agree?
When the Moon is far from the Sun after conjunction and sets well after it, the two methods nearly always agree: the crescent is easy to see and the calculation says the month has begun. When conjunction is close to sunset, the calculation's condition may be met while sighting fails, and this is the source of most one-day differences. In some cases the crescent cannot be seen by eye at all because it is too close to the Sun, and sighting and calculation bodies agree to complete the month.
Is there scholarly disagreement?
Yes, and it is a well-known jurisprudential question: whether a sighting in one country applies to all, or each country has its own, and whether calculation may be relied on to confirm, to deny, or only as a guide. We neither issue rulings nor favour a view here; follow the announcement of your official body and muftis. What hijriGO provides is calculated information for planning, not a religious ruling.
How hijriGO handles the difference
- It uses Umm al-Qura and says so on every page.
- Each event carries a status: Calculated (follows directly from the month date), Expected (calculated but depending on sighting or announcement in your country, such as Ramadan and the two Eids), Officially announced (shown only once a documented announcement is entered with its source; none are entered at present), or Traditional date (a disputed matter such as the Prophet's birthday).
- It offers a day adjustment: if your authority announces that Ramadan starts a day after the Umm al-Qura date, choose "add a day" and the date card, calendar and countdowns all change, with your choice saved only in your browser.
| What it tells you | What it does not tell you |
|---|---|
| The Umm al-Qura Hijri date of any day | What your authority will announce on the night |
| The expected date of Ramadan and the Eids and the days remaining | A religious ruling on the start of a month |
| The status of each date: calculated, expected, traditional | Official announcements (we enter one only with its source) |
Planning tips
- Plan Ramadan and Eid with a one-day margin: do not book travel or a crucial appointment on the calculation alone.
- Follow your official body's announcement on the evening of the 29th of Sha'ban and Ramadan.
- If you live abroad, note that your country of residence may follow a different method from your home country.
- Add event dates to your phone calendar and move them a day after the announcement (see How to add a Hijri event to your phone calendar).
Common questions
Can the calculation come later than the announcement? Very rarely. Usually the astronomical calculation either matches the announcement or precedes it by a day.
Which is more accurate, sighting or calculation? The question is not only scientific accuracy; calculation is precise about the Moon's position, but treating it as a legal cause for a month's start is a jurisprudential matter, while sighting is tied to the text but affected by sky and observer. We do not take sides.
Why can Eid differ even if Ramadan matched? Because Ramadan starts by an announcement and then lasts 29 or 30 days depending on the sighting on the 29th evening, so Ramadan may match the calculation while Eid does not, or the reverse.
For the expected date of the next Ramadan with a countdown, open the Ramadan countdown, and for other dates see Islamic events. For our approach, see calculation method and the date disclaimer.