The first day of menstrual bleeding is designated as "day 1" of the menstrual cycle. If we look at 100 average fertile couples with a prior pregnancy who time intercourse in relation to ovulation, we’ll find that 20-25 of those couples have a positive pregnancy test. One month later 15-20 more couples will get pregnant and, in theory, at the end of 4 months all 100 couples should be pregnant. In reality %85-90 of these women become pregnant at the end of the year. It is generally accepted that a couple whose chances of conceiving are lower than 20-25% are diagnosed as infertile. When a couple has a 5% chance of getting pregnant each month, even if they time intercourse according to ovulation, their chance of conceiving will be much lower spontaneously.