Andrew Samwick notes that the Social Security Trustee's Report probably understates future longevity rates. The implication, it would seem, is that Social Security could be in even worse shape than people expect.

But here's an honest question: would longer lifespans for old people necessarily put Social Security in a tighter bind? After all, you would think that much of this lifespan gain might come from people living healthier lifestyles in their prime years (diets, not smoking, etc.), which would decrease a lot of expenses later in life and enable people to get by with relatively smaller benefits. (Obviously this isn't true if obesity rates continue to rise.) Then there's disability. Presumably, health care will get better and better, and disabilities will fall, which eases the strain on the Social Security program—by enough to make up for the longer lifespans. That seems to be what's going on here, if I understand the Trustee's report correctly.

Meanwhile, if health care is getting better and better, doesn't this mean that productivity for working Americans is getting better and better too? (Better health care leads to better productivity, but better productivity also leads to better health care!) So that puts Social Security on a more stable footing. I don't know how to get at more exact numbers or projections though.