What is the failure rate of using both condoms and birth control pills?

Answer 1

==How did THAT happen?== I have a friend whose husband did not want any children at all. So she took the Birth Control pill and he used condoms every single time they had sex. Well, they had two children, a boy and a girl. She said that she has no idea how that happend, but it did. A paternity test might offer a clue. ==General answer== If you know the failure rates for both methods you can calculate the failure rate for combining them, theoretically. Let's say Method A is 90 percent effective. That means that ten percent of the women using the method will get pregnant in any one year. Let's say Method B is only 80 percent effective, so its failure rate is 20 percent per year. The failure rate of both methods employed together, however, is the product of the failure rates, 0.1 x 0.2, or 0.02. Subtract that from one, and you get the effectiveness of the combination: 0.98. Pretty darn impressive. Of course, this assumes that the methods are compatible. Some non-latex condoms are not compatible with spermicides, so using them together could increase the failure rate.