The short answer: Yes — no birth control method except sterilization is 100% effective, though if you use birth control correctly and consistently your chances of getting pregnant are extremely low.
When taken exactly as recommended, the pill can be up to 99% effective — meaning that only 1 out of every 100 women who take the pill will get pregnant in a given year. However, some women miss pills, which reduces the pill’s actual rate of efficacy to about 91%. To be its most effective, the pill needs to be taken every single day, and in the case of the minipill (progestin-only pills) the pill should be taken within the same three-hour window every day.
When used correctly, the birth control ring (NuvaRing) is 99% effective at preventing pregnancy. If you don’t put in your new NuvaRing on time or the NuvaRing is out of your vagina for more than 48 hours when you’re supposed to have it in, the effectiveness will decrease.
The birth control patch is 99% effective with perfect use, but 91% effective with “typical” use, meaning that out of 100 women who use this method each year, about nine will get pregnant. If you replace your patches on schedule you decrease your likelihood of unintended pregnancy.
The birth control shot is approximately 94% effective in regular use, and is most likely to be effective if you stay on schedule with your shots. If you forget to get your shot within 15 weeks of your last one, you might get pregnant unless you use another method of birth control. You will also need to take a pregnancy test before receiving your next shot if you have had sex more than 15 weeks after your last shot.