Part of why the 62/70 solution works is something known as joint mortality. Consider a husband and wife, both born on Jan. 1, 1950. When they become eligible for Social Security at 62, the wife will have a projected life expectancy of 84 years and 8 months. That roughly means there's a 50% chance she'll live that long (roughly, because the median life span is not necessarily the average life span). The husband's life expectancy will be 81 years and 10 months. But there's a 50% chance one spouse will die before 78 and a 50% chance the second will hold on until almost 89, the Government Accountability Office calculates. So, in effect, a woman who takes Social Security at 62 isn't necessarily accepting a smaller payout until 84, but only (on average) until her husband (or she) kicks off shy of 78.
