How can a woman calculate her menstrual cycle?

For a woman regarding menstrual blood, she is either a beginner (mubtada’ah), in which case she abstains for the duration she sees blood, up to fifteen days. Or she is accustomed (mu'tadah), and there are three scenarios for her:

1. She has a regular habit: She acts according to her habit.

2. She can distinguish menstrual blood: She acts according to what she has distinguished.

3. She has neither a habit nor the ability to distinguish: She refers to the common menstrual period of women (six or seven days).

The evidence for this detailed explanation comes from prophetic hadiths that specify how to deal with menstrual blood based on a woman's habits, her ability to distinguish, or by referring to the common condition of women.