Cycle Day

The term "cycle day" refers to a specific point in a woman’s menstrual cycle. Cycle day starts with day one of a period, which is the first day of bright red bleeding, and usually lasts around 21-35 days.

Tracking of a menstrual cycle day-by-day along with monitoring physical characteristics like basal body temperature and cervical mucus can help to pinpoint the brief window that a woman is fertile and most likely to become pregnant.