The Pill
This guide gives effectiveness percentages for two categories of contraceptive use: typical use, which includes people who may not always use a method exactly how and when they were supposed to use it, and perfect use, which indicates how effective the method would be if it were always used correctly.
Perfect use: Out of 100 women who use the pill correctly at all times, maybe 1 and probably no one in the group might become pregnant in one year.
Typical use: For typical users, 8 women out of 100 might become pregnant when using the pill for one year.