Infertile days are days within your monthly cycle that there is no chance for pregnancy at that time.
Fertile days are days that there is a possibility for conception.
Within the fertile days there is a peak day which is the most fertile day of all. Having sex during your fertile time and insuring that you hit the peak day will greatly enhance your ability to conceive. This page will help you identify your fertile and peak days. Most Fertile Time Fertile days within a monthly cycle are a few days before ovulation. What makes them fertile is the type of cervical fluid that is produced by the hormone estrogen.