What's the correct time to have sex to conceive, that is before or after periods?

~6-14 days after end: Conception can only occur after ovulation which may be punctuated by mittelschmerz ~14 days after the menses begin. In addition male spermatozoa can survive for 3-5 days in the female genital tract. When you combine these facts with the usual 28-day female cycle, you come up with the recommendation to maximize sexual activity ~6-14 days after the end of menstruation in order to achieve conception.