How effective is the diaphragm at preventing pregnancy?

The diaphragm is a pretty effective method. For those who use it perfectly every single time they have sex, it’s around 84% effective. For the typical user (and by typical, we mean the way most end up using it), effectiveness is closer to 83%.

In other words:

For people who use the diaphragm exactly as directed for a year, about 16 in 100 will get pregnant when they don’t want to during the first year they use the diaphragm.

For people who use the diaphragm as people typically use it, about 17 in 100 will get pregnant when they don’t want to during the first year they use the diaphragm.