The looming fiscal cliff threatens to boost taxes by more than $500 billion in 2013 when many temporary tax provisions are scheduled to expire. Nearly 90 percent of Americans would pay more tax, primarily because the temporary cut in Social Security taxes and many of the 2001/2003 tax cuts would expire. Low-income households would pay more due to expiration of tax credits in the 2009 stimulus. High-income households would be hit hard by higher tax rates on ordinary income, capital gains, and dividends and by the new health reform taxes. And marginal tax rates would rise, potentially affecting economic decisions.