It depends on who you ask!
According to the U.S. government, in 2013, 14.5 percent of U.S. households were below the “poverty threshold.”
Poverty threshold depends on number and age of members of household. (At one time it was the cost of “three nutritious meals” per day but the computation is a bit more complicated now.) In 2013, it was over $5,000 annual income per person ($13.7 per day) in a nine-person household, and more for smaller households. If you lived alone and were under 65, it was just over $12,000 per year ($33.20 per day).
I get these numbers from Income and Poverty in the United States: 2013 (Census Bureau). See pages 13 and 43 for details.
Concidentally, the world-wide poverty rate in 2011, according to the World Bank was also 14.5%. However, they defined poverty as income of $1.25 per day per person (U.S. dollars). One billion people with income less than one-tenth of what U.S.A. considers poor!
What if we double the World Bank’s poverty threshold (making it 7.5 to 18% of U.S. threshold)? Well, I’m not sure how to get current numbers, but ten years ago, 2.7 billion people were under two dollars per day per person, and one billion were under a dollar a day.