Ahead of yesterday's telecast of his interview with talk show icon Oprah Winfrey, where he is expected to come clean on doping, the figure of between $100 million and $125 million has been widely circulated.

It's the range often cited, without attribution, by such mainstream media as the New York Times, USA Today and the Wall Street Journal.

But senior editor Kurt Badenhausen of Forbes magazine said it's difficult to work out how rich he is, given that he holds no big stakes in publicly listed companies, no longer races for prize money and has lost lucrative sponsorships.

Forbes, famous for its rich lists, estimated Armstrong's net worth at $28 million back in 2005, the year he began his four-year hiatus from cycling, and $20 million in 2009, when he made his Tour de France comeback.

In more recent years, Badenhausen told AFP, Armstrong has probably been earning around $15 million a year from sponsors, public appearances and speaking fees.

"With someone like Lance, it's a little tricky to work out his net worth," he said. "Nobody is talking in his camp these days."

Armstrong lost big-time sponsors like Nike sportswear and Trek bicycles when the US Anti-Doping Agency last year put him at the heart of what it called the biggest doping conspiracy in sports history.

But he is understood to retain small equity interests in companies that he has been associated with, such as energy drink manufacturer FRS.

His principal home in Austin, Texas, an opulent estate spread over 1.13 acres (0.45 hectares), has an assessed value of $3.147 million, according to local property records seen by AFP.

The 8,000 square foot (745 square meter) Spanish-style villa with swimming pool and a media room -- where he hung his framed Tour de France yellow jerseys along the wall -- was featured in the July 2008 issue in Architectural Digest.

"Other than some bikes in the garage, you wouldn't know who lives here," he told the glossy upscale magazine.

Not unusually for a celebrity crib, the house is held in the name of a trust. It has been among the top 10 residential water users in Austin, the local American-Statesman newspaper has reported, citing water utility data.

Armstrong has other real estate holdings in Austin as well, plus a retreat in Hawaii where he has competed in Ironman triathlons.