i saw it a site: What is the Rhythm Method? The rhythm method, also known as "fertility awareness," is a method of birth control that uses the menstrual cycle to predict your most fertile time of the month - that is when you are most likely to become pregnant. Once you have identified your most fertile time you simply don't have sex or use a barrier method of birth control during that time period. How does it work? Fertility awareness birth control methods are based on the fact that: sperm may live in the female reproductive tract for up to 7 days the female egg lives for only a day fertilization may occur even days after intercourse "safe days" occur 2 days after ovulation and continue until your next period safe days? what is your percentage of not pregnating the girl in those "safe days"? 87%? does it mean you can f# without the condoms on those safe days with a high chance of not impreg her?