When are women the most fertile?
Women are most fertile shortly before and on the day of ovulation. A study of couples looking to become pregnant had women keep a fertility journal of when they had intercourse. At the same time, they underwent sensitive hormone tests to determine the exact day of ovulation and sensitive pregnancy tests. Researchers then identified several hundred instances where a single act of intercourse led to pregnancy.
They found that pregnancy occurred when couples had intercourse up to six days before ovulation until the day of ovulation. There were no pregnancies before or after that time period. The highest chance for pregnancy was when intercourse occurred either two days before, one day before, or on the day of ovulation.