Medicare Costs

From 1965 Advisory Council Report:

Again let us adjust the 2000 estimate for inflation, which would make the estimate contribution total from workers and employers $20.6 billion. The actual 2000 figure for is $128 billion (not including supplementary medical insurance which tacks on another $89 billion. It's not clear from the Advisory Council report whether the Supplementary insurance is included in the above estimate, but I couldn't find a separate estimate for it).

Only off by a factor of 6.

Social Security Costs

From the 1941 Social Security Trust Report:

Annual benefit payments may be expected to increase from an average of about $0.3 billion for the first 5 years to almost $1 billion for the second 5 years. After a 40-year period, average annual benefit payments may have risen to a magnitude of about $3.5 billion and, after a 50-year period to over $4 billion. A further rise after that period may be expected because of the anticipated increase in the number of persons qualifying for benefits and in the average benefit payments.

Let's assume that these numbers are not inflation adjusted (and there was a serious bout of inflation between 1941 and 1991). The $4 billion estimate for social security benefits in 1991 would be equivalent to $38 billion in 1991 dollars.

The actual amount paid out in social security benefits in 1991 was $387 billion.

Off only by a factor of ten.