The economy of the United States is the world's largest national economy. Its nominal GDP was estimated to be $14.3 trillion in 2009, approximately a quarter of nominal global GDP. Its purchasing power parity was also the largest in the world, approximately a fifth of global GDP at purchasing power parity. The U.S. economy also maintains a very high level of output per capita. In 2009, it was estimated to have a per capita GDP (PPP) of $46,381, the 6th highest in the world.
Historically, the U.S. economy has maintained a stable overall GDP growth rate, a low unemployment rate, and high levels of research and capital investment funded by both national and, because of decreasing saving rates, increasingly by foreign investors. It has been the world's largest national economy since 1870 and remains the world's largest manufacturer, representing 19% of the world's manufacturing output. In 2009, consumer spending, coupled with government health care spending constituted 70% of the American economy. About 50% of the entire world's millionaire population reside in the United States. Furthermore, 40% of the world's billionaires are American. The US is also home to the world's largest stock exchange, the New York Stock Exchange. It also boosts the world's largest gold reserves and the world's largest gold depository, the New York Federal Reserve Bank. The United States is also home to 139 of the world's 500 largest companies, which is almost twice that of any other country. A large contributor to the country's success has also been a very strong and stable currency. The US Dollar holds about 60% of world reserves, as compared to its top competitor, the Euro, which controls only about 24%.
Since the 1960s, the United States economy absorbed savings from the rest of the world. The phenomenon is subject to discussion among economists. Like other developed countries, the United States faces retiring baby boomers who have already begun withdrawing from their Social Security accounts; however, the American population is young and growing when compared to Europe or Japan. The United States public debt is in excess of $13 trillion and continues to grow at a rate of about $3.83 billion each day. Total public and private debt was $50.2 trillion at the end of the first quarter of 2010, or 3.5 times GDP. Domestic financial assets totaled $131 trillion and domestic financial liabilities totaled $106 trillion.
The American labor market has attracted immigrants from all over the world and has one of the world's highest migration rates. The United States is ranked second, down from first in 2008-2009 due to the economic crisis, in the Global Competitiveness Report. The country is one of the world's largest and most influential financial markets, home to major stock and commodities exchanges like NASDAQ, NYSE, AMEX, CME, and PHXL.