The White Days: Fasting the 13th, 14th and 15th

The White Days (Arabic Ayyam al-Bid) are the 13th, 14th and 15th days of each month in the Hijri calendar. Many Muslims fast them voluntarily, based on hadith in which the Prophet ﷺ named these three dates for the monthly three-day fast. They fall in the middle of the lunar month, when the moon is at or near full, which is where the name "white" comes from. Because Hijri months follow the moon, the White Days fall on different Gregorian dates every month, so the easiest way to find them is a Hijri calendar.

Key Takeaways

• The White Days are the 13th, 14th and 15th of every Hijri month.
• Sahih al-Bukhari records the Prophet ﷺ advising a fast of three days each month; narrations in an-Nasa'i, at-Tirmidhi and Abu Dawud name the 13th, 14th and 15th.
• Sahih Muslim reports that the Prophet ﷺ himself was not particular about which days of the month he fasted, so the three days are a recommendation, not the only option.
• From Jumada al-Thani to Dhu al-Hijjah 1448, every calculated full moon falls on one of the three White Days.
• 13 Dhu al-Hijjah is a day of Tashriq, when fasting is prohibited, and in Ramadan the White Days are already part of the obligatory fast.

What the hadith say about the White Days

The texts come in two layers. The sahih collections establish a monthly three-day fast. Narrations in the Sunan collections then name which three days.

A fast of three days every month

In Sahih al-Bukhari 1981, Abu Hurairah says his close friend, the Prophet ﷺ, advised him to do three things: fast three days a month, pray two rak'ahs of Duha, and pray witr before sleeping. Al-Bukhari placed this narration in a chapter titled "To fast the 13th, 14th and 15th of the lunar months."

In Sahih al-Bukhari 1979, the Prophet ﷺ told Abdullah ibn Amr, who was fasting every day, that "The fasting of three days (a month) will be equal to the fasting of the whole year." The same narration warns against fasting every day of the year.

The narrations that name the 13th, 14th and 15th

Several narrations specify the dates. All four below were checked on sunnah.com, which shows the grading given by the editors of each translated edition.

The Arabic of an-Nasa'i 2420 uses the phrase ayyam al-bid directly, and the Abu Dawud narration uses al-bid, which the sunnah.com translation renders as "the days of the white (nights)."

The Prophet ﷺ also fasted other days of the month

In Sahih Muslim 1160, Mu'adha al-Adawiyya asked Aisha whether the Prophet ﷺ fasted three days in every month. Aisha said yes. When asked which days, she said he was not particular about which days of the month he fasted.

Read together, these texts are usually understood this way: fasting any three days in a month follows the sunnah, and the 13th, 14th and 15th are the days specifically named. How strongly to prefer those three dates, and how to weigh the narrations against each other, is a matter for scholars. Ask a qualified scholar or your local mosque if you need a ruling for your own situation.

Why they are called "white": the full-moon link

The name points to the moon. A Hijri month begins with the new crescent, so by the 13th to 15th the moon has had about half a lunar cycle to grow. Those nights are lit by a full or nearly full moon from dusk to dawn. The sister post on moon phases through an Islamic month walks through that cycle day by day.

The match is close but not exact. The US Naval Observatory's moon phases data service gives the instant of each full moon in Universal Time (UT). Set against the calculated Umm al-Qura dates, the full moons for the rest of 1448 AH look like this:

Hijri dates are calculated from the Umm al-Qura tables in the open-source hijri-converter library (@tabby_ai/hijri-converter) that this site uses. Full-moon times are from the USNO data service. Local announcements of the month may differ by a day, and the full moon's local date depends on your time zone: the Rajab full moon at 01:28 UT, for example, falls on the evening of 23 December in the Americas.

In every month in the table, the full moon lands on the 13th, 14th or 15th. That is a property of the lunar cycle, not a rule: the fast follows the Hijri date, not the moment of full moon. You do not need to see the full moon or check its time to fast the White Days.

How to find the White Days each month

Finding the dates takes two steps.

1. Find the 1st of the month. Open the Hijri month in a calendar, such as the calculated Jumada al-Thani 1448 calendar, or check the announcement your local mosque follows.
2. Count to the 13th, 14th and 15th. If your community started the month a day later than the calculated calendar, every White Day moves a day later too.

Keep sunset in mind when you plan. Islamic dates begin at sunset, so the 13th starts on the evening before it appears on a Gregorian calendar. The fast itself is kept during daylight, from dawn to sunset, on the Gregorian day shown: for Jumada al-Thani 1448, that means fasting Monday 23, Tuesday 24 and Wednesday 25 November 2026, with suhoor before dawn each morning. The sister post on why the Islamic day begins at sunset explains the convention.

A worked example: Jumada al-Thani 1448

The calculated 1 Jumada al-Thani 1448 is Wednesday 11 November 2026. Counting forward:

• Sunday evening, 22 November: the 13th begins at sunset.
• Monday 23 November: first fast (13th).
• Tuesday 24 November: second fast (14th). The full moon is at 14:53 UT.
• Wednesday 25 November: third fast (15th).

If your mosque announced the month a day later, shift each day by one: fast Tuesday, Wednesday and Thursday instead.

Months that need a different plan

Two months change the usual pattern.

Ramadan. The 13th to 15th of Ramadan are already fasted as part of the obligatory month, so there is no separate White Days fast to add. In 1448 AH those dates are calculated as 20 to 22 February 2027.

Dhu al-Hijjah. The 13th of Dhu al-Hijjah is the last of the days of Tashriq, the three days that follow Eid al-Adha. In Sahih Muslim 1141a, the Prophet ﷺ says, "The days of Tashriq are the days of eating and drinking," and the chapter heading for that hadith on sunnah.com describes it as the prohibition of fasting those days. In 1448 AH, 13 Dhu al-Hijjah is calculated as Wednesday 19 May 2027. People who want to keep three days that month usually choose other dates, such as the 14th, 15th and a following day. Which days to substitute is a question to put to a scholar you trust.

Common questions

Is fasting the White Days obligatory?

No. It is a voluntary fast. The narrations above recommend it, and Sahih Muslim 1160 shows the Prophet ﷺ fasting three days a month without fixing them to particular dates.

Can I fast three other days if I miss the White Days?

The hadith in Sahih al-Bukhari 1981 speaks of three days a month without naming them, and Aisha's report in Sahih Muslim 1160 says the Prophet ﷺ was not particular about which days. Many people who miss the 13th to 15th fast three other days that month. Some combine the monthly fast with Monday and Thursday fasting.

Does the full moon have to fall on the 14th?

No. The full moon can fall on the 13th, 14th or 15th, and its local date depends on your time zone. The fast is tied to the Hijri date, not to the exact moment of full moon.

Plan your next White Days

Before each month starts, open the Hijri month in the calendar, note the 13th, 14th and 15th, and set reminders for suhoor on the mornings before. If your mosque announces the month a day later than the calculated date, move all three fasts by one day. To see how the moon will look on those nights, check the moon phases page, and use the date converter for any month not shown in the table above.