WASHINGTON (REUTERS) - President Barack Obama and his wife Michelle earned a gross income of US$477,383 (S$650,000) in 2014, according to the couple's tax returns, released by the White House on Friday.

Their income is down from US$503,183 in 2013 and US$662,076 in 2012.

Obama's annual presidential salary is US$400,000 and much of his outside income has been attributed to sales of his biographies, which may be declining.

The Obamas reported US$43,722 in income from overseas.

The White House did not immediately respond to questions on the source of the overseas income.

The Obamas paid US$93,362 in total tax, paying a federal income tax rate of 19.6 per cent.

In donations to charity, the Obamas gave US$70,712 to 33 different groups. The largest donation was US$22,012 to Fisher House Foundation, which provides housing to military families while a loved one is receiving treatment.

Vice-President Joe Biden and his wife Jill, a community college professor, also released their tax returns on Friday, reporting a combined income of US$388,844.