President Barack Obama is a millionaire roughly seven times over, despite dwindling book sales and a surprisingly high interest rate on his mortgage.

President Barack Obama makes a face as he reads the book “Where the Wild Things Are” during the 2014 White House Easter Egg Roll on the South Lawn of the White House. Obama was worth up to $7 million in 2013, according to a newly released financial disclosure form, and he owes much of that fortune to royalties collected on his several published books. (AP/Carolyn Kaster)

According to a financial disclosure form released by the White House Thursday, the Obama family’s assets were worth up to $7 million in 2013.

Obama held the biggest chunk of his assets — up to $5 million — in Treasury bills.

Much of the presidential fortune has been fueled by steadily decreasing royalties from Obama’s books. In 2013, his memoir “Dreams From My Father” generated between $50,001 and $100,000 in royalties, while “The Audacity of Hope” generated less than $50,000. “Of Thee I Sing: A Letter To My Daughters” brought in less than $15,000 in royalties.

The Obamas paid $98,169 in taxes on a total income of roughly half a million dollars last year, according to the president’s 2013 tax return.

The president’s 2013 income is a far cry from 2009, when he raked in $5.5 million, largely from book sales. Last year, most of Obama’s income came from his $400,000 presidential salary.

The White House also released a financial disclosure form for Vice President Joe Biden, which showed he made less than $201 in royalties on his 2007 book “Promises to Keep” in 2013.

While the president may trounce the vice president when it comes to book sales, Biden has the financial upper hand when it comes to mortgage rates: Biden refinanced the mortgage on his Wilmington, Delaware, home last year to get an interest rate 2 percentage points lower than the 5.625 percent rate the president pays on his Chicago mortgage.

Despite lower prevailing mortgage rates — and his own advice and admissions – Obama has not refinanced since purchasing his home in 2005.