It's difficult to give an exact estimate but experts believe that the morning-after pill is approximately 98-99% effective However, the statistics of being pregnant rests greatly on where you are in your menstrual cycle. You are only fertile at the time of ovulation. If 100 women each had a single act of unprotected intercourse on one day in the middle of their cycle and then take the morning-after pill, only 2 to 3 will get pregnant. Also - The earlier you take it the better; it works best if taken within 24 hours of unprotected sex.