President Barack Obama, a Democrat, defeated the Republican candidate following a campaign that cost more than $2 billion overall.
Obama's re-election effort had $14.2 million left as of November 26, according to the Federal Election Commission disclosures.
Leftover campaign cash is common and often goes to the national party or other candidates.
The Romney campaign on Thursday said every raised dollar had gone toward Romney's run and that it "continues to process invoices for pre-election expenses." It expected to have less than $1 million by the end of the year.
"It is not uncommon. It is of course a great risk," said Sheila Krumholz, executive director of the Center for Responsive Politics that tracks campaign finance. "As a loser you want to make sure you've given it your all."
Obama and Romney both spent much of their campaign cash on voter outreach and especially advertising. But the Democrat and his "Super PAC" backers at Priorities USA Action, an unlimited-spending group, held an early advertising game advantage.
Obama's campaign dominated the airwaves, booking the increasingly expensive spots earlier and at the lowest price.
The "super" political action committee, which was legally barred from coordinating with the campaign, ran a series of aggressive ads about Romney's private equity past that portrayed him as a corporate raider.
The damaging ads, as well as negative press surrounding Romney's disparaging "47 percent" comment about Americans relying on government funds, contributed to the candidate's defeat.
The pro-Romney Super PAC Restore Our Future - boosted once again by this year's Republican mega-donor Sheldon Adelson - plowed $45.5 million into a last-ditch effort to sway voters, according to Thursday's filings.
But according to Reuters/Ipsos polling, nearly three-quarters of Americans had made up their minds in the presidential race before Obama and Romney faced off in the first debate on October 3.
The pro-Obama group spent $20.9 million from October 18 and had $4.3 million in cash on hand as of November 26, according to the FEC filings. Romney's Restore Our Future reported having $842,062 left.
Adelson, billionaire chief executive of Las Vegas Sands, and his wife Miriam contributed another $10 million to Restore Our Future, accounting for nearly half of all the group's last-minute fundraising and bringing the couple's total gift to the Super PAC to $30 million.
Adelson's total donations to Republican candidates and organizations, although not all of them are disclosed, are said to have topped $100 million this election cycle. He planned to spend "that much and more" in the next campaign, he told the Wall Street Journal earlier this month.
The pro-Obama Super PAC received 11th-hour $1 million infusions from two of its own top donors, media mogul Fred Eychaner and Houston lawyer Steve Mostyn. They brought Eychaner's total to $4.5 million, and Mostyn's to $3 million, according to FEC filings.
