most hormonal methods are 99.9% effective when used CORRECTLY. most people don't use birth control correctly. user error is the most common cause of unplanned pregnancies when on birth control, cited from planned parenthood. I've been on the mini pill, taking it correctly, for the last 15 months with no condoms and no pull out. It's 99.5% effective with perfect use I have not gotten pregnant. It's as effective as female sterilization. the other hormonal methods are 99.9% effective when used correctly which is as good as male sterilization. there's a VERY SMALL margin of error for failure. if you're getting pregnant on birth control you're most likely using your method wrong. that includes not checking your strings monthly when you have an iud.