With a typical amount of deviation in the time of ovulation, the rhythm method still allows 1-2 weeks per month with very low risk of pregnancy. Combined with w

With a typical amount of deviation in the time of ovulation, the rhythm method still allows 1-2 weeks per month with very low risk of pregnancy. Combined with withdrawal when the risk is unacceptably high, it can be acceptably effective. > "fertility awareness" (on its own) is a less reliable means of contraception than most other options You're absolutely correct, of course - but some people's situations don't require such a high level of reliability. For instance, my wife and I used the rhythm method for four years after marriage without incident, until we decided to try for our first child. During that time an unexpected pregnancy would not have been unwelcome. We weren't where we wanted to be financially, but we would have been fine. Our ballpark assumption of a 10% chance of conception per year was an acceptable level of risk to outweigh the negatives of a barrier method or hormone-based option.