How accurate is the pregnancy calendar for calculating your day of conception?

well i don't know if it work but i know about its depend on you rather---let say you have a 28 cycles your chance to get pregnant will be up to 14 days after your last period and you count from the first day of your last it takes from 8 days to 16 days after your period-- you should make your owed calender you should write down when you start to ovulation how long your period last...was it spotting medium-heavy period--this well also help you to get pregnant also... i wish you the best of luck