Explanation

Ovulation is expected to occur at the 12^(th) -14^(th) day of the menstrual cycle. Probable ova releasing day is 12-14 day of menstrual phase, and sperm can live for 2-3 days in female reproductive system. So, 10-17 days are the most probable days for fertilisation. Draw backs of periodic abstinence The effectiveness of this method is limited because only a few women have regular menstrual cycle and the actual time of ovulation can not be produced as the ovulation in humans occurs about 14 days before the onset of the next menstruation