chances with birth control

Ok my girlfriends has been on birthcontrol since she was 14 and she is now 16, what would the chances of her getting pregnant if we had sex without a condom but i didnt come inside her..yes i do precum a good bit but are the chances really high or what..i know its stupid to take the risk int he first place but im just wondering

 

will somebody please answer

 

birth control is 90% effective if used properly.

 

Actually, 99% effective if used exactly as stated.

Peace and love