My Cycles are irregular. My cycle is not 28 days. The best days are the 2 days before ovulation as well as the day of ovulation itself. Under favorable conditions sperm can live for a few days inside a woman's body and this is why the days preceding ovulation are considered fertile days. The catch is that in order for sperm to survive that long the woman must already have cervical fluid that is highly fertile in its quality.
Every woman is unique.
And every woman who is fertile does produce this fertile quality cervical fluid at some time each month. Whether you are one of the Fertile Myrtles or not, you can, and should , learn to observe your body's fertility signs in order to determine when your cervical fluid is of fertile quality. Many women actually feel ovulation. It can be a dull ache or a sharper pain. It may linger for a few hours or it may last momentarily.