There are basically three differences between men and women’s fertility, though God only knows how many other types of differences there are (we’ll just have to save that for another blog).

For starters, boys aren’t born with any sperm at all. They only start producing them when they reach puberty. Girls, on the other hand, are born with all the eggs they will ever have, but don’t start releasing them until puberty.

In addition, men are fertile all the time, since they produce millions of sperm on a daily basis, whereas women are fertile only a few days per cycle since an egg is basically released only once a cycle. In a vacuum, we’d say that a woman is therefore only fertile one day per cycle, which is the potential lifespan of the egg. Yet because she produces fertile-quality cervical fluid leading up to ovulation, sperm can survive in it for a few days longer to ultimately fertilize the egg.

Finally, there’s the issue of just how long fertility lasts over the years. Men are fertile from puberty until they die. Women, on the other hand, are fertile from puberty until menopause (about 51 years old), although, in reality, they are only capable of sustaining a pregnancy until about a decade before they stop menstruating. This explains why you often hear about older (heck, who am I kidding?) OLD men fathering babies with wives half their age.