From the CBO, another major variable that would have to be estimated far into the future, any changes in real benefits:



This shows their estimates for changes from now until 2075.

More interesting information from the same location regarding the estimates for death rates:

"Life expectancy for people currently age 65 is estimated to be 83 years. In 2035, it is estimated to be 85 years, and in 2075, 87 years. "

So, for people who actually live long enough to receive benefits, they currently expect them to, on average, collect them for 18 years. They only expect this figure to grow by TWO YEARS over the next 31 years, and by a mere FOUR years over the next 71. I'm sorry, but that is insane. With so many exciting new medical fields in their infancy, and so many prospective wonder drugs in trials right now, and so many new insights into the human body opening up, and they seriously think this (not to mention the inevitable advances that aren't even contemplated yet) is only going to add a measley four years to life expectancy??

I knew they were lowballing it, buy I had no idea how absurd the numbers were.