Min & Max Time Frames
A woman’s menstrual cycle can vary in length. On average, a woman menstruates for 3-8 days, and her subsequent purity can range between 21-28 days. These fluctuations are fine as long as they fall within the fixed limits established by Islamic law (Shari’ah). As a woman has her menstrual cycles, it is extremely important that she record the respective dates of any bleeding: menstruation (hayd), post-natal bleeding (nifas) and irregular bleeding (istihada). She should also write down her purity (tuhr) dates as a record for future reference.
The Fiqh of It