Singers Carrie Underwood, Adam Lambert and Chris Daughtry top Forbes' list of top-earning American Idols.

According to Forbes, American Idol season four winner Underwood raked in $20 million over the past year, making the country music singer the highest paid Idol alum.

Lambert and Daughtry, who each earned $6 million, tied for a second place finish on the list.

Lambert, the 29-year-old American Idol season 8 runner-up, concluded his worldwide Glam Nation tour to support his freshman album For Your Entertainment with a performance in London, England. He played 116 dates in 12 months.

After Idol's conclusion, Lambert confirmed rampant media speculation that he's gay in an interview with Rolling Stone. In an E! True Hollywood Story hour-long special, Lambert talked about his decision to share his personal life with his fans.

“My fans have been really supportive of my choice to be open and upfront about my sexuality and my lifestyle,” Lambert said. “I have come from the belief that hiding something from people and manipulating what they think of you is far more offensive and disrespectful than just being upfront and being who you are.”

Forbes estimated the singers' incomes based on data from Pollstar, RIAA and others, as well as interviews with industry insiders.

R&B singer Fantasia Barrino, who won American Idol's third season, earned $4 million, while Jordin Sparks, the show's youngest winner at 17, raked in $3 million.