Clinton earned nearly $40 million in speaking fees in the past six years, the Washington Post (NYSE:WPO) said Friday, giving nearly a speech a day in 2006.

Last year, however, about 80 percent of his 352 talks were said to be for no fee or for donations to the non-profit William J. Clinton Foundation for various causes, the Post said.

The former president addressed a variety of audiences in the United States, for which he often got $150,000 per speech, and groups abroad where he could command more.

Many of Clinton's six-figure speeches were made to top backers of his wife, Sen. Hillary Clinton, D-N.Y., who is seeking the Democratic presidential nomination.

The Clintons are estimated to be worth as much as $50 million, according to disclosure forms from Hillary Clinton.