In the U.S. today, there are 23 elderly people for every 100 working-age people. That ratio has been rising for decades — and it's projected to nearly double by 2060.
This is a problem. Working-age Americans pay for programs like Medicare that support the elderly. So the more that ratio rises, the heavier the burden is for working Americans.
The problem is not unique to the U.S. In fact, it's a much bigger problem for many other developed countries.
I knew the broad outlines of this story. But when I talked about it recently with Gerhard Heilig of the UN's population division, one thing surprised me: Populations are aging mainly because people are having fewer and fewer babies, not because life expectancy is increasing.
The graph below shows the very clear, two-stage process that lots of countries are going through: First, people start having fewer babies. Then, over the following decades, the ratio of elderly people to working age people goes up and up and up. The U.S. is the orange circle; other countries are color-coded by region.
Note: The graphic below requires flash and may not appear for some mobile users.