How is the menstrual period determined for a woman who regularly experiences bleeding for less than three days or more…

According to the Hanafi school, bleeding that lasts less than three days or more than ten days is not considered menstruation but istihada (irregular bleeding). (Mevsılî, el-İhtiyâr, 1/26-27; Ibn Nujaym, el-Bahr, 1/201) In the Shafi'i school, the minimum duration for menstruation is one day and the maximum is fifteen days. (Shirbini, Mughni’l-muhtâj, 1/278)

According to information provided by gynecology and obstetrics specialists, although rare, some women may regularly experience bleeding for less than three days or more than ten days. If a woman regularly has bleeding for less than three days or more than ten days, and this is supported by medical examination, it is appropriate for her to consider bleeding that lasts between less than three days and up to fifteen days as menstruation.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu