Why three days a month, every month, can carry the reward of fasting an entire year.
Published September 4, 2026 · Reviewed by the Ihsabha Editorial Team
Among the many voluntary fasts recommended in the Sunnah, Ayyam al-Beedh — literally "the white days" — stands out for being one of the simplest to keep up consistently: just three specific days, every single Hijri month. Because these three days are pinned to the lunar calendar rather than the Gregorian one, the actual calendar dates shift every month, which is the main source of confusion for anyone trying to plan around them in advance.
The name refers to the brightness of the moonlit nights around the middle of the lunar month, when the moon is closest to full and the nights are lit up ("white") rather than dark. Because the Islamic calendar is lunar, the middle of every month reliably falls on the same three dates on the Hijri calendar — the 13th, 14th, and 15th — regardless of which Hijri month it is or what season it falls in on the Gregorian calendar.
Multiple hadith describe the Prophet ﷺ encouraging the fasting of three days from every month, with several also specifying these three particular dates by name, tying the practice directly to the brightest nights of the lunar cycle. Because the recommendation is attached to the Hijri date rather than any Gregorian equivalent, the same three numbered days recur every month without exception, which is what makes Ayyam al-Beedh one of the more structured and easy-to-remember voluntary fasting patterns compared to other Sunnah fasts.
The virtue commonly cited for this practice ties back to a broader principle: a single good deed is rewarded as ten, so fasting three days is credited as equivalent to fasting an entire month of thirty days. Repeating this every month across a full Hijri year effectively multiplies out to the reward of fasting the entire year — twelve months' worth of reward from a total of only thirty-six actual fasting days, spread out three at a time.
The Hijri calendar is purely lunar, running about 10 to 12 days shorter than the Gregorian solar year. Because the White Days are fixed to Hijri dates rather than Gregorian ones, their equivalent Gregorian dates drift backward by roughly that same 10-to-12-day margin every solar year, and shift slightly between consecutive Hijri months as well due to 29- versus 30-day lunar months. Over a period of about 33 solar years, the White Days cycle through every season and Gregorian month before returning to roughly where they started.
Yes. If someone is only able to fast one or two of the three days due to illness, travel, work, or any other valid reason, the fast still counts and still carries reward proportional to what was completed, even if the full virtue described for all three days together isn't reached. Likewise, someone who missed the 13th-15th entirely but fasts any three days elsewhere in the same lunar month is still understood to fulfill the broader "three days a month" sunnah described in some narrations, even though the specific virtue tied to the White Days themselves is associated with these particular dates.
Because Ayyam al-Beedh and the separate sunnah of fasting on Mondays and Thursdays run on independent cycles — one lunar-date-based, the other weekday-based — they occasionally overlap, meaning one of the three White Days might land on a Monday or Thursday in a given month. When this happens, a single day's fast fulfills both intentions at once, which is a convenient, though not required, way to combine two recommended practices without adding an extra fasting day to the month.
There's one important exception worth knowing: the White Days of Dhul Hijjah can potentially overlap with the Ayyam al-Tashreeq (the 11th, 12th, and 13th of Dhul Hijjah), during which fasting is not permitted for anyone not performing a specific Hajj-related ritual. In a month where the 13th falls within this prohibited window, that particular day should not be fasted even though it's technically one of the White Days, and only the 14th and 15th would be fasted that month instead.
In one Hijri month, the 13th, 14th, and 15th might correspond to, say, March 3rd, 4th, and 5th on the Gregorian calendar. The following Hijri month, the same three Hijri dates will typically fall roughly 10 to 11 days earlier on the Gregorian calendar — closer to February 21st, 22nd, and 23rd — since the lunar month is shorter than the solar month it's being compared against. Anyone tracking White Days by memory of a fixed Gregorian date from a previous month will find themselves consistently off by roughly this margin.
Skip the manual date conversion. Ihsabha's White Days Calculator converts the 13th, 14th, and 15th of any Hijri month into their exact Gregorian dates, so you always know which days to fast without tracking the lunar shift yourself.
Fasting even one of the three days still counts and carries its own reward; the specific virtue described for the White Days as a set applies most fully when all three are completed, but a partial fast is far better than skipping the month entirely and is valid in its own right.
No. Ayyam al-Beedh is a voluntary (sunnah) fast, not an obligatory one. There's no sin in not fasting them, though they are strongly recommended as an easy, structured way to gain consistent extra reward throughout the year.
Since White Days are voluntary rather than obligatory make-up fasts like Ramadan qada, there's no requirement to make them up on a missed month. Someone in this situation can simply resume fasting them in a later month once they're able to, without needing to "catch up" on missed months.
No. Since Ramadan is itself an entire Hijri month observed with obligatory fasting throughout, the concept of separately fasting the 13th-15th as a voluntary practice doesn't apply that month — every day of Ramadan is already a fasting day.
As with any voluntary fast, a general intention to fast for the sake of the specific sunnah is sufficient, and unlike Ramadan, this intention doesn't need to be fixed the night before — it can be made anytime before midday on the day itself, provided nothing has been eaten or drunk since dawn.
The exact Gregorian date for any Hijri date can vary by a day depending on which moon-sighting method or regional authority is followed, since the start of each Hijri month is itself subject to some regional variation. For most planning purposes this makes no practical difference, but it's worth checking your local moon-sighting announcement if you need the White Days to align exactly with a specific community's calendar.