The New York Times says Donald Trump paid just $750 (£587) in federal income tax both in 2016, the year he ran for the US presidency, and in his first year in the White House.
The newspaper – which says it obtained tax records for Mr Trump and his companies over two decades – also alleges that he paid no income taxes at all in 10 of the previous 15 years.
The records reveal “chronic losses and years of tax avoidance”, it says.
Mr Trump called the report “fake news”.
“Actually I paid tax. And you’ll see that as soon as my tax returns – it’s under audit, they’ve been under audit for a long time,” he told reporters after the story was published on Sunday.
“The IRS [Internal Revenue Service] does not treat me well… they treat me very badly,” he said.
Mr Trump has faced legal challenges for refusing to share documents concerning his fortune and business. He is the first president since the 1970s not to make his tax returns public, though this is not required by law.
The Times said information in its report was “provided by sources with legal access to it”.
The report came just days before Mr Trump’s first presidential debate with Democratic rival Joe Biden and weeks before the 3 November election.