Most people think Social Security operates on a simple principle. While you work, you pay taxes. The more you pay, the fatter the checks you cash once your retire.
But the system is much more complicated. And because of the way Social Security was set up in the 1930s, it doesn’t benefit everyone equally. The biggest winners are spouses who stay at home — for the most part, women. The losers are married couples in which both spouses work, as well as some people who are unmarried or divorced.
Social Security benefits in part reflect how much people have paid into the system through payroll taxes during their careers. Yet among couples who have paid the same amount into the system, those with one earner can draw tens of thousands of dollars more in lifetime benefits, compared to households with two earners.
– The Washington Post