If your partner pulls out perfectly every single time, then withdrawal is about 96% effective. This is [a hard method to get perfect](http://bdsdr.me/QF8hWc), though, so it's more likely that withdrawal will be around 78% effective.
Of those women who use withdrawal exactly as directed, about 4 in 100 will experience an accidental pregnancy during the first year they use this method.
Of those women who do not use withdrawal exactly as directed, about 22 in 100 will experience an accidental pregnancy during the first year they use this method.