What is the "fiscal cliff"?

These include $50 billion in delayed impact from the initial round of cuts and $78 billion more in the so-called "sequester."

Expiration of payroll tax cut--$115 billion

The payroll tax that underwrites Social Security and Medicare was temporarily cut from 6.2 percent to 3.1 percent in December 2010, and that cut was extended through the end of this year in February 2012. The expiration of this tax cut will be felt as a 3.1 percent reduction in income for low- and middle-income families, more than the typical pay increase. It will mean a significant drop in real income.

Expiration of extended unemployment benefits--$39 billion

These benefits were coupled to the payroll tax cut as "stimulus" measures in both the December 2010 and February 2012 bipartisan agreements, but in the second deal the Democrats accepted a Republican demand to reduce the duration of extended benefits from 99 weeks to the current 73 weeks for the hardest-hit states, and from 93 weeks to only 63 weeks for most states.

Now, even this inadequate level of benefits for the long-term unemployed is set to end, under conditions where more than five million workers have been out of work for six months or longer. One million long-term unemployed workers who have exhausted all state benefits will lose their extended federal benefits January 1, and a further one million will lose benefits in the first quarter of 2013.

Expansion of the Alternative Minimum Tax--$114 billion

The AMT, first enacted in the 1960s as a measure against tax evasion by the super-rich, was never indexed for inflation, so tens of millions of upper-middle-income families could now come under its provisions. Congress has repeatedly adopted temporary "fixes" to delay imposition of the tax, most recently in December 2010, limited to taxes on 2011 income.

If another "fix" is not adopted, or the AMT is not fully indexed for inflation retroactively, the number of families required to pay the AMT will rise from four million to 30 million next year, sharply increasing the tax bills these families will pay for income earned in 2012.

Expiration of miscellaneous tax provisions--$120 billion

As many as 80 provisions of the 2009 stimulus legislation introduced by the Obama administration and enacted by a Democratic-controlled Congress, or adopted in subsequent deals in December 2010 and February 2012, have either expired this year or will expire January 1. Most of these are incentives to business -- $109 billion -- while a small fraction, about $11 billion, represents tax credits or expanded deductions for working families.

Mandated cuts in Medicare reimbursement--$14 billion

The 1997 Balanced Budget Act, negotiated by the Clinton administration and then-House Speaker Newt Gingrich, established what was titled the Medicare sustainable growth rate, or SGR, to restrain the growth of payments to health-care providers under Medicare. The SGR provision has never actually been put into practice, as pressure from hospitals and the American Medical Association has induced Congress to enact repeated versions of one-time provisions known in Washington jargon as the "doc fix."

The most recent versions were incorporated into the December 2010 and February 2012 bipartisan agreements under the Obama administration. The latest one expires on January 1, 2013. If the much lower ceiling is imposed, with Medicare reimbursement cut by 27 percent, many doctors and hospitals may stop accepting new Medicare patients and even phase out treating current patients.