How is the menstrual period calculated, especially the ten days, with intermittent bleeding due to the IUD?

The majority of scholars hold that the maximum duration of menstruation is fifteen days and nights. Blood that appears during this period is considered menstrual blood, even if it is intermittent. If the bleeding stops and complete purity is achieved, you must perform ghusl (definition) (ritual bath) and pray. If the blood returns within the fifteen-day period, it is still considered menstruation. However, if the bleeding exceeds fifteen days, then you are considered to be in a state of istihadha (non-menstrual vaginal bleeding). In this case, you should differentiate between menstrual blood (which is black, thick, and has an odor) and istihadha blood (which is red and odorless). If you are unable to differentiate, then you should refer to your usual known habit. Otherwise, you should refer to the predominant habit of the women in your family. Anything beyond that is considered istihadha. In such a case, you should perform ghusl after the typical duration of your menstruation has passed and then do what a woman in istihadha does, which is to perform wudu (ablution) for each prayer.