Donald Trump could have avoided paying federal income taxes for as along as 18 years, according to a leaked tax document obtained by the New York Times.
The Republican presidential candidate's tax forms have been a major issue in the campaign because, unlike other modern-day nominees for the White House, he has refused to make them public.
Trump claims he cannot release them because he is being audited by the US tax authority, despite the fact there is no law or precedent to preclude their release. President Richard Nixon released his records while under audit in 1973.
The New York Times reported late Saturday that it had received Trump's 1995 income tax returns, in which he declared a 916-million-dollar loss due to failed business ventures.
Tax experts hired by the paper concluded that "rules especially advantageous to wealthy filers would have allowed Mr Trump to use his 916-million-dollar loss to cancel out an equivalent amount of taxable income over an 18-year period."
Trump's critics have accused him of hiding something in his tax returns that could be damaging to his presidential bid.
At their first debate last week Democratic nominee Hillary Clinton speculated he was not releasing them because they could reveal "he's not as rich" or "charitable as he claims."
She also said that they might show "he's paid nothing in federal taxes," to which Trump interjected: "That would make me smart."
A Trump campaign statement said the Times had "illegally obtained" the document, but it did not dispute the report.