Time until one expected pregnancy for some birth control methods. Rates are for typical use.
Unprotected: 7 months
Spermicide: 3 years
Withdrawal: 5 years
Diaphragm and spermicide: 6 years
Condom: 6 years
Calendar method: 8 years
NuvaRing: 11 years
Contraceptive patch: 12 years
Birth control pill: 12 years
Depo injection: 32 years
Copper IUD: 125 years
Tube tying: 200 years
Progestogen IUD: 500 years
Combined injection: 500 years
Vasectomy: 650 years
Implant: 2,000 years
The Rationalist Conspiracy 
Withdrawal is more effective I expected, Birth control pill less than I expected. Lol at the numbers greater than 125, Transhumanism isn’t quite there yet.
And how do we calculate the expected values for *combining* methods? Say, condom + pills?
My guess: 6 years * (12 years / 7 months) = 123 years. Not too shabby.
That depends on whether the odds are dominated by the contraceptive not working properly, or it being misapplied/forgotten. If the first, they’re probably uncorrelated. If second, then I’d expect significant correlation, so it might turn out the condom isn’t helping much.
For this particular example i’d expect some correlation – say she might forget to take the pill and he might forget the condom if they’re both partying and drinking a lot at the time. So 50 – 100 years?
The most important fact left out: what is the frequency of intercourse to produce these stats? If you’re having unprotected sex every day, you’re extremely likely to hit at least a few days of fertility in the female and you’d expect pregnancy to occur almost certainly within a month.