The estimated present value of the cash needed to keep the Medicare hospitalization fund solvent over the next 75 years has fallen to $4.9 trillion this year, from $5.4 trillion a year ago.
The new "unfunded obligation" figure amounts to 22 percent of the $21 trillion in benefits Medicare hospitalization fund trustees now expect the fund to have to pay out from 2013 through 2087.
The unfunded obligation is about 1.11 percent of the $428 trillion in taxable payroll that the trustees expect U.S. workers to earn between now and 2087. The trustees call that 1.11 percent figure the hospitalization trust fund's "actuarial balance."
The Medicare program trustees have given the new figures in their 2013 annual report.
A year ago, in the 2012 annual report, trustees were estimating that the trust fund would pay about $21 trillion in benefits from 2012 through 2086, and that Americans would earn $411 trillion in taxable payroll over that period.
The actuarial balance figure given in the 2012 report was 1.35 percent.
The trustees are now expecting U.S. workers to pay $14 trillion in payroll taxes over the 75-year projection period, up 5 percent from the total they used last year.
The total amount of assets the Medicare trust fund actually has on hand has fallen to $220 billion, from $244 billion.