Hillary Clinton has released her tax returns, adding to the pressure on her Republican rival for the White House, Donald Trump, to do the same.

The Democratic presidential candidate paid an effective federal tax rate of 34.2 per cent last year.

Her running mate Tim Kaine, along with his wife Anne Holton, paid a rate of 20.3 per cent, his returns show.

Trump, a real estate developer with a fortune estimated to be in billions, has refused to release his.

Presidential candidates typically release their tax returns to the media to show their effective tax rate, charitable donations and other financial details.

Trump, who has released a self-reported financial disclosure form, said he will not make his tax returns public until the Internal Revenue Service completes audits of them.

Clinton’s return was filed jointly with her husband former President Bill Clinton. The couple earned more than $10 million in 2015, the documents say.

Bill and Hillary Clinton made most of their money in 2015 from business income, namely consulting, speaking and book royalties, for a total of $10.1 million between the couple.

Bill spent $500,000 in travel as part of the speaking portion of his business, Hillary had about $250,000 in travel expenses for her speaking business.

Half of their deductions are charitable giving, including a $1 million donation to the Clinton Foundation

The IRS has said Trump is free to release his returns. Trump would be the first presidential candidate in decades not to release his returns.

Then-President Richard Nixon released his tax returns in 1973, starting an informal precedent.

In 2012, then-Republican presidential Mitt Romney reluctantly released his returns.

The returns became a campaign issue after the documents showed he paid an effective tax rate of 14.1 per cent, much lower than the typical rate for top earners.

"Hillary Clinton and Tim Kaine continue to set the standard for financial transparency,” said a Clinton campaign spokeswoman, who called on Trump to do the same.

Most of the income came from Clinton’s speaking fees as Hillary has been campaigning for president. Hillary earned about $3m from book royalties.

The Clintons have disclosed tax returns for every year since 1977.

Agencies