There's no formula that can tell you that you have an 85% chance of becomming pregnant if you have sex on the first day, last day, middle day you ovulate... If you have sex without protection while you are fertile and you are a relatively healthy woman of childbearing age, you have a very good chance of becoming pregnant.

i am 19 and my boyfriend is 43 i know strange but we are so much a like it was love at first sight we have an awesome relationship. is the age thing maybe a problem with getting pregnant

No, normal, healthy men do not have problems with fertility until they reach their sixties or seventies.