How to Calculate the Purity Period between Two Menstruations.

Hanafi Fiqh

Answered by Shaykh Yusuf Weltch


My bleeding began on the 15th day after my last period. I observed istihada on that day, but I wasn’t sure when the 15th day would begin, which would affect what prayers I offered during istihada versus my period. I didn’t know to check for purity at every prayer on the last day of my last period. I waited until ‘Asr to ensure dryness after the previous day before performing the ghusl.

My most recent period (after istihada) lasted three days, from the 7th to the 10th (purity at dhuhr time). Because I checked for purity at asr 14 days prior (the 6th being the 15th day of purity), I counted my period as starting after the 7th of Dhuhr.

Does this count as three full days because I only checked at ‘Asr and not Dhuhr during my last period?


In the Name of Allah, the Most Merciful and Compassionate.

One must calculate the time based on hours to determine one’s menstrual period and the period of purity between two menstruations.

The Legal Separating Purity (al-Tuhr al-Sahih)

For menstruation to be valid, it must be preceded by at least 15 days (i.e., 360 hours) of complete purity. [Birgivi, Dhukhr al-Muta’ahhilin]

If there were 360 hours between the time your previous menstruation ceased and the new instance of bleeding on the 6th of the month, then the bleeding of the 6th, 7th, 8th, 9th, and 10th is considered menstruation. [Ibid.]

The Non-Separating Purity (al-Tuhr al-Fasid)

If, however, there was not a total of 360 hours between the first instance of bleeding and the second— all of the first and second are added together, as well as all the days that transpired between them. [Ibid.]

This is based on the principle: Any bleeding that goes beyond the habit (explained below) and continues beyond the maximum length of valid menstruation, ten days— then an amount equal to days of the habit considered to be menstruation, and the remainder is irregular bleeding.  [Ibid.]

For example:

If your first instance of bleeding was four days, after that, 14 days of purity passed (as your mentioned), then you experienced bleeding for an additional three days— all of this time is added together (4 + 14 + 3 = 21).

21 is far beyond the maximum menstruation, so the amount of days of your most recent valid menstruation (i.e., the menstruation before the four days) is the number of days from the 21 that is considered menstruation.

For example:

If the most recent menstruation before the four days was six-day menstruation, this marks your habit (‘ada) as six days. The habit is essential to keep track of as it will be used to reconcile any confusion in further menstruation.  

The remaining days are all considered irregular bleeding (istihada), and you will retroactively make up any prayers not performed in those days.

Summary: Reasonable Surety

Looking back to calculate the exact amount of time of purity between the two instances of bleeding may be difficult. The Islamic legal axiom says, “When certainty is not possible, one must recourse to the reasonable surety.” [Ibn Nujaym, al-Ashbah wa al-Nazair]

If you cannot make an exact assessment of the number of hours, try your best to make the most educated guess that you are reasonably sure to be the correct assessment. Use that number to perform the calculations as mentioned above. Nothing more than this is required of you.

Hope this helps
Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani

Shaykh Yusuf Weltch is a teacher of Arabic, Islamic law, and spirituality. After accepting Islam in 2008, he then completed four years at the Darul Uloom seminary in New York where he studied Arabic and the traditional sciences. He then traveled to Tarim, Yemen, where he stayed for three years studying in Dar Al-Mustafa under some of the greatest scholars of our time, including Habib Umar Bin Hafiz, Habib Kadhim al-Saqqaf, and Shaykh Umar al-Khatib. In Tarim, Shaykh Yusuf completed the memorization of the Quran and studied beliefs, legal methodology, hadith methodology, Quranic exegesis, Islamic history, and a number of texts on spirituality. He joined the SeekersGuidance faculty in the summer of 2019.