In the female reproductive system, the menstrual/ovulation cycle is a recurring cycle of physiologic changes that occurs in reproductive-age females - Wikipedia
This tool was developed to help woman to get pregnant, however it also can be used as a calendar based contraceptive method. The Woman Calendar generates 6 useful charts based on the woman's menstrual cycle data:
Luteal phase or Menstruation
Free Sex Days: The time with the lowest pregnancy percentage.
Fertility: The time with the highest likelihood of sexual intercourse leading to pregnancy.
Ovulation: Presence of female mature egg that is capable of being fertilized.
Conception Boy: Highest chance to get pregnant with a Boy.
Conception Girl: Highest chance to get pregnant with a Girl.