Depends on the woman. Typical cycles are 28 to 35 days. A woman with amenorrhea may not have one at all. A woman with PCOS may skip months at a time. OR...a woman can be in menopause and not have one due to the natural aging process. That being said...standard answer for a woman with no health issues or age related issues or MENTAL issues such as a man claiming to be a woman....would be 12.