How to Fast
Fasting (Sawm) is a prescribed duty in the Qur’an intended to develop moral restraint, awareness of God, and spiritual discipline (2:183). The Qur’an specifies when fasting begins and ends each day, who is exempt, and how missed days are to be compensated. This page describes how to fast based on the Qur’an alone.
Preconditions
Before fasting begins, a few foundational points apply:
• Fasting during Ramadan is prescribed for believers (2:183–185).
• The fast is observed from dawn until night (2:187).
• The fasting month begins and ends based on the lunar month.
• There is no Qur’anic requirement for crescent sighting.
• Exemptions and compensations apply (2:184–185).
Determining the Start of the Fasting Month
The fasting month is Ramadan, which is a lunar month (2:185). In the Islamic lunar system, the day begins at sunset. Determining the beginning of Ramadan therefore depends on the beginning of the new lunar month.
According to the Qur’an, months are lunar, but the Qur’an does not specify crescent sighting. The beginning of the lunar month can be determined by astronomical new moon data as follows:
If the astronomical new moon (conjunction) occurs before sunset, the new lunar day begins at that sunset.
If the astronomical new moon occurs after sunset, the new lunar day begins at the following sunset.
This method does not rely on hadith, visual moon sighting, or testimony. It uses objective astronomical data and reflects the sunset-beginning of the lunar day.
Astronomical Data Source
Astronomical new moon times can be obtained from the U.S. Naval Observatory (USNO) Moon Phases Table.
No Requirement for Crescent Sighting
The Qur’an does not require:
• crescent sighting
• local or global visual confirmation
• community testimony
These requirements are rooted in hadith tradition, not in the Qur’an. Therefore, calculating the lunar month using astronomical data is consistent with Qur’an-only methodology.
When the Daily Fast Begins
The Qur’an states in 2:187:
“Eat and drink until the white thread of the dawn becomes distinguishable from the black thread. Then you shall fast until night.”
From this verse, fasting begins at true dawn, not at sunrise. The distinguishing of white and black thread refers to the appearance of dawn light against the darkness of night, corresponding to astronomical dawn.
When the Daily Fast Ends
The same verse commands fasting “until night.” Night begins at sunset. The Qur’an does not instruct delaying the breaking of the fast beyond sunset. Therefore, the fast ends at sunset.
What Invalidates the Fast
The Qur’an explicitly mentions food and drink as invalidators of the fast (2:187). Intentionally eating or drinking during fasting hours breaks the fast.
The Qur’an does not list other invalidators such as:
• bodily functions
• accidental swallowing
• medical injections
• brushing teeth
These come from jurisprudence outside the Qur’an and are not included here.
Exemptions, Substitute Days, and Compensation
The Qur’an provides clear flexibility for those who cannot fast:
“Anyone who is ill or traveling, and wishes to do so, may substitute the same number of other days.” (2:184)
“For those who can afford it, a substitute of feeding the needy.” (2:184)
“God wishes you convenience, not hardship.” (2:185)
This establishes three points:
Illness and travel allow postponement.
Missed days are to be made up later.
Feeding the needy is a compensation option for those unable to fast.
Compensation does not apply to those who can fast later; it applies to those genuinely unable to fast.
Summary of Qur’an-Based Fasting Practice
Determine the start of Ramadan using lunar month calculation.
Eat and drink until dawn.
Abstain from food and drink from dawn until sunset.
Break the fast at sunset.
Make up missed days if exempted for valid reasons.
Provide compensation if permanent inability exists.
End fasting when the next lunar month begins.