The IOU that's being laid on the doorsteps of U.S. taxpayers in the form of the national debt is far greater than most Americans realize.

For those who have gotten lost in the sea of numbers -- and who can blame you -- here are a few that aim to simplify the issue and illuminate the full extent of the nation's debt load:

At last count, the national debt was about $15.7 trillion, according a Treasury statement released on June 11 this year. That works out to about $50,100 for each of the 313 million residents in the country.

Factor in all of the federal government's debt obligations -- money that it owes to cover expenses related to Medicare, Social Security, Treasury securities and bonds issued by government-sponsored agencies like Fannie Mae, Freddie Mac and Ginnie Mae -- and the national debt balloons to $79.2 trillion -- a figure you'll never hear government agencies utter. That means a baby born today in the world's richest economy begins her life with a virtual debt burden of about $253,000.

Medicare Benefits

The biggest part of the undisclosed national debt is Medicare, a program that includes $38.6 trillion in promised future benefits that exist currently as unfunded liabilities, according to a recent Medicare Trustee report.

One of the costly features of the Medicare deficit is the prescription drug benefit, an outpatient program enacted by the Medicare Modernization Act after Republican Pres. George W. Bush signed it into law in 2003. The drug benefit has churned out liabilities of $7 trillion -- which remain off the government's balance sheet. A large portion of the remaining $31 trillion comprises costs of funding Medicare hospital coverage shortfalls, over the next 75 years.                   

Health care costs are growing faster than the economy. We're not sure how to control that, said Susan Irwing, director for Federal Budget Analysts at the Government Accountability Office.

Employer and employee tax revenues, which are struggling to keep pace with rising costs and an aging population, are exacerbating the Medicare shortfall.

Congress produces 10-year budget projections, which do not provide a full picture of Medicare costs in terms of their long-term trajectory, said Josh Gordon, a policy director at Concord Coalition, a nonpartisan fiscal policy organization founded by the late Sen. Paul Tsongas (D-Mass).

If the current path continues, the hit to the GDP will be so large that it will knock the economy back into a recession, Gordon added. But elected officials probably won't make this a priority until after the elections.

Social Security

Social security programs like pension and insurance schemes face unfunded benefit payments of $8.6 trillion over the period 2012-2086, according to the 2012 Annual Report of the Board of Trustees of the Federal Old-Age and Survivors Insurance and Federal Disability Insurance Trust Funds. The government is legally barred from using general tax revenues to pay for these benefits.

These (liabilities) are not included in the government's annual balance sheet because they come from government spending programs, which the Congress could modify every year, said Marc Goldwein, a policy director at the Committee for a Responsible Federal Budget (CRFB), another nonpartisan fiscal policy analysis group. They aren't legal obligations.

Last year, Congressional Budget Office (CBO) projections revealed that the Social Security Fund would not only raise public debt by about $600 billion between now and 2020, but would also go bankrupt by 2035. The government is currently funneling $105 billion in general revenues into Social Security trust funds to compensate for the payroll tax cuts enacted last December. Yet, this will not be enough to reduce the deficit significantly because of interest payments on outstanding national debt.

 Public-held Debt

Treasury and agency securities fall in the ambit of government debt. Treasury debts are obligations paid by the government on the basis of semi-annual interest payments. Agency debts are securities issued by federal home loan banks and government-sponsored agencies. Treasury and agency securities eventually become debts held by the public.

At the end of 2010, the government had $9.4 trillion in treasury debt and $7.5 trillion in agency securities, leading to a total sum of $16.9 trillion in public-held debt, according to Washington think tank American Enterprise Institute (AEI). These debts are not included in the government's balance sheets.

Forecasts of changes in public-held debt, relative to U.S economic output, do not project an accurate picture of the current fiscal situation, said Alex Pollock, a resident fellow at the AEI.

Agency debts impose huge risks on taxpayers because of inaccuracies in budgeting for credit losses. The Federal Credit Reform Act seeks to monitor the costs of federal credit programs through direct and guaranteed loan programs to government-sponsored agencies. According to the Act, federal entities are required to reflect the best-guess estimates of their expected losses as costs in the government budget. The costs of these credit assistance programs are grossly understated, finance and public policy experts say.

A key problem in determining these debts is the difficulty the government faces in estimating how many mortgage loans it is financing and guaranteeing will be defaulted on. For bookkeeping purposes, Washington regularly assumes there will be zero defaults, a practice that is guaranteed to further mask the actual size of the total national debt.

Federal accounting standards take little cognizance of the need to incorporate market risks while assessing the costs of credit, a government spokesperson said. These risks include volatilities in financial markets, shifts in productivity and employment and changes in the public's expectations of future economic conditions.

Additional Payments on Borrowings to Bridge Fiscal Deficits

In addition to undisclosed debt amounts from the foregoing categories, there are net interest outlays that will bite the government on its back. These outlays are interest payments on the total amount of gross debt. They do not include interest that the government receives on loans and advances. Fluctuating interest rates would lead to a percent rise in these outlays. Since interest costs are low, these payment obligations are hardly a concern for the government today. If interest rates rise in the future, net interest payments on borrowings made to finance the gaping fiscal deficit will increase four-fold over the next ten years from $197 billion 2010 to $778 billion in 2020, according to a CBO report in 2010. This will do no favors for long-term fiscal welfare and economic growth.  

Finally, raising federal tax rates among the more affluent is not going to help the government meet its payment commitments by adding significantly to its revenue pool, economists say. We need to slow the growth of entitlement programs and introduce consumption taxation to supplement income taxes as a potential revenue source, said Eric Toder, an advisor at the Urban-Brookings Tax Policy Center and a former deputy assistant secretary for tax analysis in the U.S Treasury.

With all these obligations taken into account, a very different picture of the federal debt and fiscal deficit comes into view. Indeed, this picture could be seen as so alarmingly expensive, that there's little wonder the government would prefer to hang it in on the wall of a hideout where few people ever look.