WASHINGTON (AFP) - President Barack Obama and his wife have doubled their income since he took office, declaring a joint gross income of 5.5 million dollars for the 2009 fiscal year, the White House said Thursday.

The average annual household income in the United States was around 50,303 dollars in 2008, according to official figures.

Obama earned an annual salary as president of 374,460 dollars since his inauguration in January 2009, according to his tax filings released Thursday.

But most of his income came from his books, which have leaped to the top of the bestseller lists since he first started running for the White House.

In 2008, Obama and his wife, Michelle, declared a joint gross income of 2.65 million dollars, most of which also came from royalties on his books "Dreams of My Father" and "The Audacity of Hope."

According to his 2009 documents, the Obamas paid 1.79 million dollars in federal taxes and 163,303 dollars in state taxes to Illinois where the couple owns a home in Chicago.

April 15 is the date set by which all Americans and US residents must file their annual tax returns to the Internal Revenue Service.

Obama also received 1.4 million dollars last year when he won the Nobel Peace Prize, but he has donated his prize money among 10 charities, the White House said, and the sum is not part of the 5.5 million dollars declared income.

The couple also donated 329,100 dollars to 40 different charities in 2009, with the largest reported gifts being 50,000 dollars to CARE and the United Negro College Fund.

In 2007, the Obamas said they had earned 4.2 million dollars.

The first couple's filing contrasted strongly with the more meager tax returns of Vice President Joe Biden and his wife, Jill, who declared 333,182 dollars in joint income for 2009.

That was still an increase from 2008 when their joint income was 269,256 dollars. They also gave some 4,820 dollars to charity, or some 1.4 percent of their incomes, the White House said.

The average annual household income in the United States was around 50,303 dollars in 2008, according to official figures.