well most birth control pills work primarily by stopping you from ovulating so that even if a sperm finds its way into the fallopian tube there won't any egg to fertilize. (birth control pills cause other subtle reproductive tissue changes that decrease the risk of pregnancy as well. ) this means when you're on the pill you don't have any "fertile days " the way you do when you're ovulating. taken correctly birth control pills are 99. 9% effective in preventing pregnancy. however the pill does not protect you from contracting a sexually transmitted disease. so please always practice safe sex by using a condom. i hope this answers your question!
if i am on the pill can i accurately use the calendar method to determine my fertile days to avoid pregnancy?