Also note: A 2% or 4% chance of pregnancy is pretty good odds using only condoms for 1 year. If using only condoms for 10 years that number is creeping up on 20% or 40%.

This is a weird one as well because you aren’t taking into account fertility. Say someone gets into a serious relationship at 25, if your’re a women your fertility starts to decrease slightly in your late 20s and even more so after you hit 35.