WASHINGTON — President Obama and first lady Michelle Obama watched their income fall and their federal tax rate go up in 2013, according to IRS returns released Friday.

In a joint filing, the couple reported an adjusted gross income of $481,098, down $127,500 from 2012. The Obamas have seen a steady drop in income during their White House years, largely a result of slowing book sales for the couple. Both have published best-sellers.

The Obamas paid $98,169 in federal taxes, down from $112,214 in 2012. But their effective tax rose from 18.4 percent in 2012 to 20.4 percent last year.

The lower income and bigger tax bite came with less money for charity this year. The Obamas donated $59,251 to 32 charities, or 12.3 percent of their adjusted gross income. Last year, they gave $150,034, or 24.6 percent of their adjusted gross income, to a similar list of charities. The recipients this year included Habitat for Humanity; the American Red Cross; St. John’s Church, an Episcopal church near the White House; and Sidwell Friends, the Obama daughters’ private school.

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Obama’s government salary was $394,796. The first lady is not paid. The additional income came from book sales.

The White House also released Vice President Joe Biden’s tax returns. Biden and his wife, Jill, reported $407,009 in combined adjusted gross income, mostly from salaries. Jill Biden is a professor at Northern Virginia Community College.

The Bidens reported charitable contributions of $20,223, more than $15,000 of which went to the USO, proceeds from the sales of a book written by Jill Biden.