Women are paid, on average, only seventy seven cents for every dollar earned by men. As can be seen at the site of “moms rising”, even larger differentials exist for women who are mothers, and these are most extreme for women who are single mothers. But where do these numbers come from? How are they calculated, and, more importantly, what assumptions are made in performing those calculations? I will discuss how these wage differentials, which many of us have encountered in our own professional careers, are calculated.