When is a woman the most infertile?

A woman is generally most infertile during the time outside her ovulation window, which typically occurs around the midpoint of her menstrual cycle. Specifically, she is least fertile during the menstrual phase (the first few days of her period) and the luteal phase after ovulation, when the egg is no longer viable. Additionally, fertility declines with age, particularly after the age of 35, making women less fertile overall in their late 30s and 40s.