What are the chances of getting pregnant while taking the birth control pill responsibly?

1/333 women annually: For women taking birth control pills (ocp's) properly and consistently, the chance of pregnancy is reported to be 0.3% per year, or 1 pregnancy in 333 women each year. The actual pregnancy rate in the "real world" is reported to be at least 3% on ocp's, or 1 pregnancy in 33 women each year.

Pregnancy on pill: The birth control pills are about 99% effective when taken properly and not interfered with by certain conditions e.g. Taking certain antibiotics, or anti-fungal agents or if the pill is missed or vomited up within an hour of taking it etc. About 8 out of 100 couples per year will have a pregnancy while taking birth control pills as directed.