This is according to the yearly trustees' report released last week by the Treasury Department.

The impending insolvency is largely due to a 3 percent downward revision of the country's gross domestic product and labor productivity in the decade to come. The report warns that unless Congress intervenes and makes some changes to the program, more than 66 million Americans could face a reduction of between 23 and 25 percent in their benefits.

Medicare is also facing a shortfall. According to the report, the hospital insurance trust fund of Medicare (Part A), which covers inpatient hospital stays, only has enough funds to cover its full scheduled benefits until 2031. This is when its reserves will be depleted, but ongoing income should allow the program to pay out 89 percent of scheduled benefits.

Another big problem that Medicare and Social Security are contending with is the aging American population. Fewer workers have been paying into the program lately to support the rising number of beneficiaries. At the same time, healthcare is becoming more expensive, and people are living longer and needing benefits for more years than in the past.