How effective is Depo (the shot) at preventing pregnancy?

The US CDC (Centers for Disease Control and Prevention) reports that for every 100 couples that use Depo as their sole form of contraception, 6 of those couples will experience a pregnancy any given year, a rate of 6%. Not too bad, but not perfect. Why?

Once again, human error. Thirteen weeks can pass quickly, and last-minute situations can arise causing delayed Depo injections. Or you might forget to put the appointment in your calendar and…whoops! You’re late on your Depo. The good news is that there is a range of dates within which it’s still okay to get the shot—so if you can’t make an appointment on a particular day in exactly 13 weeks, it’s okay! And if you know you’re late, try not to have sex (or use a backup form of contraception) until you are able to get your next shot.